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8.1: Introduction to Nutrition and Physical Fitness

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Physical fitness is a general state of health and well-being and, more specifically, the ability to perform aspects of sports, occupations and daily activities. Physical fitness is generally achieved through proper nutrition, moderate-vigorous physical exercise, physical activity, and sufficient rest. Before the industrial revolution, fitness was defined as the capacity to carry out the day’s activities without undue fatigue. However, with automation and changes in lifestyles physical fitness is now considered a measure of the body's ability to function efficiently and effectively in work and leisure activities, to be healthy, to resist hypokinetic diseases, and to meet emergency situations.

Fitness is defined as the quality or state of being fit. Around 1950, perhaps consistent with the Industrial Revolution and the treatise of World War II, the term "fitness" increased in western vernacular by a factor of ten. Modern definition of fitness describe either a person or machine's ability to perform a specific function or a holistic definition of human adaptability to cope with various situations. This has led to an interrelation of human fitness and attractiveness which has mobilized global fitness and fitness equipment industries. Regarding specific function, fitness is attributed to personnel who possess significant aerobic or anaerobic ability, i.e. strength or endurance. A holistic definition of fitness is described by Greg Glassman in the CrossFit journal as an increased work capacity across broad times and modal domains; mastery of several attributes of fitness including strength, endurance, power, speed, balance and coordination and being able to improve the amount of work done in a given time with any of these domains. A well rounded fitness program will improve a person in all aspects of fitness, rather than one, such as only cardio/respiratory endurance or only weight training.

A comprehensive fitness program tailored to an individual typically focuses on one or more specific skills, and on age- or health-related needs such as bone health. Many sources also cite mental, social and emotional health as an important part of overall fitness. This is often presented in textbooks as a triangle made up of three points, which represent physical, emotional, and mental fitness. Physical fitness can also prevent or treat many chronic health conditions brought on by unhealthy lifestyle or aging. Working out can also help some people sleep better and possibly alleviate some mood disorders in certain individuals.

Developing research has demonstrated that many of the benefits of exercise are mediated through the role of skeletal muscle as an endocrine organ. That is, contracting muscles release multiple substances known as myokines which promote the growth of new tissue, tissue repair, and various anti-inflammatory functions, which in turn reduce the risk of developing various inflammatory diseases.

Activity guidelines

The Physical Activity Guidelines for Americans was created by the Office of Disease Prevention and Health Promotion. This publication suggests that all adults should avoid inactivity to promote good health mentally and physically. For substantial health benefits, adults should participate in at least 150 minutes (two hours and 30 minutes) a week of moderate-intensity, or 75 minutes (1 hour and 15 minutes) a week of vigorous-intensity aerobic physical activity, or an equivalent combination of moderate- and vigorous-intensity aerobic activity. Aerobic activity should be performed in episodes of at least 10 minutes, and preferably, it should be spread throughout the week. For additional and more extensive health benefits, adults should increase their aerobic physical activity to 300 minutes (5 hours) a week of moderate-intensity, or 150 minutes a week of vigorous-intensity aerobic physical activity, or an equivalent combination of moderate- and vigorous-intensity activity. Additional health benefits are gained by engaging in physical activity beyond this amount. Adults should also do muscle-strengthening activities that are moderate or high intensity and involve all major muscle groups on 2 or more days a week, as these activities provide additional health benefits.

How to Determine Intensity Level using Heart Rate and Talk Test

There are many ways to determine Intensity Level but let's use Heart Rate as one way to determine how intensely you are working out. First of all, as you are sitting here reading this eBook you have a certain heart rate. If you put your two fingers on your neck, you can feel your pulse. If you count the number of beats in one minute you will have an approximation of your resting heart rate. The truth is, the exact measurement of the resting heart rate requires a a much more precise measurement but we will use this as your resting heart rate for now. Please take a minute and count your approximate resting heart rate right now! Chances are, your resting heart rate was probably anywhere from 60-90 beats per minute, right? The more physically fit your heart and lungs are, the LOWER than number will be! Why? Because your heart doesn't have to work as hard to pump the blood throughout your body so it takes fewer heart beats if you are fit.

You have probably seen heart rate monitors on treadmills and stair climber machines. You have probably seen people wearing various types of heart rate monitors on devices like the "Apple Watch" and the "fit bit" etc... these devices are estimating how intensely you are exercising by how many beats your heart has to make in a minute. The device estimates your "Maximum heart rate" as 220- your Age in years. So if you are 20 years old, the device estimates your highest heart rate as 220-20 = 200 beats per minute. Your maximum heart rate is far too high for you to try to sustain during exercise. Instead, there are "target heart rate zones" you can shoot for. If you wish to be working out at a "moderate level of intensity" you will want your heart rate to be between 50% and 70% of your maximum. If you wish to be working out at a "vigorous" level of intensity then you will want your heart rate to be between 75-85% of your maximum. Using the 20 year old example again, if 200 is your maximum heart rate, then 200 x 0.5 = 100 beats per minute for 50% of maximum and 200 x .7 = 140 beats per minute for 70% of maximum. This tells you, if you check your pulse during exercise and you count between 100-140 beats per minute you are doing "moderate intensity" level of exercise!

Another, much easier though less precise, way to estimate intensity level is the "talk test". Basically, if you are able to carry on a breathy conversation as you exercise you are probably at a moderate level of intensity. If you can not carry on a conversation because you are too winded (out-of-breath) then you are probably at a vigorous level of exercise. Many people prefer this method because it doesn't require any equipment nor does it require you to stop to count your heart beats.

Specific or task-oriented fitness is a person's ability to perform in a specific activity with a reasonable efficiency: for example, sports or military service. Specific training prepares athletes to perform well in their sports. Examples are:

• 100 m sprint: in a sprint the athlete must be trained to work anaerobically throughout the race, an example of how to do this would be interval training.
• Middle distance running: athletes require both speed and endurance to gain benefit out of this training. The hard working muscles are at their peak for a longer period of time as they are being used at that level for longer period of time.
• Marathon: in this case the athlete must be trained to work aerobically and their endurance must be built-up to a maximum.
• Many fire fighters and police officers undergo regular fitness testing to determine if they are capable of the physically demanding tasks required of the job.
• Members of armed forces will often be required to pass a formal fitness test – for example soldiers of the US Army must be able to pass the Army Physical Fitness Test (APFT).
• Hill sprints: requires a level of fitness to begin with, the exercise is particularly good for the leg muscles. The army often trains doing mountain climbing and races.
• Sand running creates less strain on leg muscles than running on grass or concrete. This is because sand collapses beneath the foot softening the landing. Sand training is an effective way to lose weight and become fit as its proven you need more effort (one and a half times more) to run on the soft sand than on a hard surface.
• Aquajogging is a form of exercise that decreases strain on joints and bones. The water supplies minimal impact to muscles and bones which is good for those recovering from injury. Furthermore, the resistance of the water as one jogs through it provides an enhanced effect of exercise (the deeper you are the greater the force needed to pull your leg through).

• Swimming: Squatting exercise helps in enhancing a swimmer's start.

In order for physical fitness to benefit the health of an individual, an unknown response in the person called a stimulus will be triggered by the exertion. When exercise is performed with the correct amount of intensity, duration and frequency, a significant amount of improvement can occur. The person may overall feel better but the physical effects on the human body take weeks or months to notice and possibly years for full development. For training purposes, exercise must provide a stress or demand on either a function or tissue. To continue improvements, this demand must eventually increase little over an extended period of time. This sort of exercise training has three basic principles: overload, specificity, and progression. These principles are related to health but also enhancement of physical working capacity.

High Intensity Interval Training consists of repeated, short bursts of exercise, completed at a high level of intensity. These sets of intense activity are followed by a predetermined time of rest or low intensity activity. Studies have shown that exercising at a higher intensity has increased cardiac benefits for humans, compared to when exercising at a low or moderate level. When your workout consists of an HIIT session, your body has to work harder to replace the oxygen it lost. Research into the benefits of HIIT have revealed that it can be very successful for reducing fat, especially around the abdominal region. Furthermore, when compared to continuous moderate exercise, HIIT proves to burn more calories and increase the amount of fat burned post- HIIT session. Lack of time is one of the main reasons stated for not exercising; HIIT is a great alternative for those people because the duration of an HIIT session can be as short as 10 minutes, making it much quicker than conventional workouts.

Cardiovascular capacity can be measured using VO 2 max, a measure of the amount of oxygen the body can uptake and utilize. Cardiorespiratory training involves movement that increases the heart rate to improve the body's oxygen consumption. This form of exercise is an important part of all training regiments ranging from professional athletes to the everyday person. Also, it helps increase stamina. Examples are:

• Jogging – Running at a steady and gentle pace. This form of exercise is great for maintaining weight.
• Elliptical Training – This is a stationary exercise machine used to perform walking, or running without causing excessive stress on the joints. This form of exercise is perfect for people with achy hips, knees and ankles.
• Walking – Moving at a fairly regular pace for a short, medium or long distance.
• Treadmill training – Many treadmills have programs set up that offers a numerous amount of different workout plans. One effective cardiovascular activity would be to switch between running and walking. Typically warm up first by walking and then switch off between walking for three minutes and running for three minutes.
• Swimming – Using the arms and legs to keep oneself afloat and moving either forwards or backwards. This is a good full body exercise for those who are looking to strengthen their core while improving cardiovascular endurance.
• Cycling – Riding a bicycle typically involves longer distances than walking or jogging. This is another low stress exercise on the joints and is great for improving leg strength.

Benefits of Fitness

Physical fitness has proven to result in positive effects on the body's blood pressure because staying active and exercising regularly builds up a stronger heart. The heart is the main organ in charge of systolic blood pressure and diastolic blood pressure. Engaging in a physical activity will create a rise in blood pressure, once the activity is stopped, however, the individual’s blood pressure will return to normal. The more physical activity that one engages in, the easier this process becomes, resulting in a more ‘fit’ individual. A "normal" blood pressure is considered to be 120/80 or below. Through regular physical fitness, the heart does not have to work as hard to create a rise in blood pressure, which lowers the force on the arteries, and lowers the over all blood pressure.

Centers for disease control and prevention provide lifestyle guidelines of maintaining a balanced diet and engaging in physical activity to reduce the risk of disease. The WCRF/ American Institute for Cancer Research (AICR) published a list of recommendations that reflect the evidence they have found through consistency in fitness and dietary factors that directly relate to Cancer prevention.

Studies have shown an association between increased physical activity and reduced inflammation It produces both a short-term inflammatory response and a long-term anti-inflammatory effect. Physical activity reduces inflammation in conjunction with or independent of changes in body weight. However, the mechanisms linking physical activity to inflammation are unknown.

Physical activity boosts the immune system. This is dependent on the concentration of endogenous factors (such as sex hormones, metabolic hormones and growth hormones), body temperature, blood flow, hydration status and body position. Physical activity has shown to increase the levels of natural killer (NK) cells, NK T cells, macrophages, neutrophils and eosinophils, complements, cytokines, antibodies and T cytotoxic cells. However, the mechanism linking physical activity to immune system is not fully understood.

Physical activity affects one’s blood pressure, cholesterol levels, blood lipid levels, blood clotting factors and the strength of blood vessels. All factors that directly correlate to cardiovascular disease. It also improves the body’s use of insulin. People who are at risk for diabetes, Type 2 (insulin resistant) especially, benefit greatly from physical activity because it activates a better usage of insulin and protects the heart. Those who develop diabetes have an increased risk of developing cardiovascular disease. In a study where a sample of around ten thousand adults from the Third National Health and Nutrition Examination Survey, physical activity and metabolic risk factors such as insulin resistance, inflammation, dyslipidemia were assessed. The study adjusted basic confounders with moderate/vigorous physical activity and the relation with CVD mortality. The results displayed physical activity being associated with a lower risk of CVD mortality that was independent of traditional metabolic risk factors.

The American Heart Association recommendations include the same findings as provided in the WCRF/ AICR recommendations list for people who are healthy. In regards to people with lower blood pressure or cholesterol, the association recommends that these individuals aim for around forty minutes of moderate to vigorous physical activity around three or four times a week.

Achieving resilience through physical fitness promotes a vast and complex range of health related benefits. Individuals who keep up physical fitness levels generally regulate their distribution of body fat and stay away from obesity. Abdominal fat, specifically visceral fat, is most directly affected by engaging in aerobic exercise. Strength training has been known to increase the amount of muscle in the body, however it can also reduce body fat. Sex steroid hormones, insulin, and an appropriate immune response are factors that mediate metabolism in relation to the abdominal fat. Therefore, physical fitness provides weight control through regulation of these bodily functions.

Regular exercise is effective for preventing the age-related decline in cognition and improving overall neuropsychological function. The increased synthesis of neurotrophic factors in the body and brain and the resulting neurogenesis in various brain structures is largely responsible for these effects. Exercise also has persistent antidepressant effects and has been found to serve as both a means to prevent and treat drug addictions, particularly psychostimulant addictions.

Menopause is the term that is used to refer to the stretch of both before and after a woman's last menstrual cycle. there are an instrumental amount of symptoms connected to menopause, most of which can affect the quality of life of the women involved in this stage of her life. One way to reduce the severity of the symptoms is exercise and keeping a healthy level of fitness. Pre or during menopause as the women body changes there can be physical, physiological or internal changes to the body. These changes can be prevented or the reduced with the use of regular exercise.

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Nutrition's Role in Physical Fitness: Why You Need to Consider Both

Barbie Cervoni MS, RD, CDCES, CDN, is a registered dietitian and certified diabetes care and education specialist.

Verywell / Alexandra Shytsman

Nutrients and Your Athletic Performance

What to eat for optimal performance, hydration makes a difference, sustainable nutrition habits, frequently asked questions.

Whether you are a competitive athlete, play a recreational sport, or practice yoga, there is no doubt that physical activity has many health benefits. When it comes to maximizing your workouts or improving athletic performance, nutrition and physical activity go hand in hand.

What we eat before and after exercise, as well as on a regular basis, can make a large difference in how we feel and how we perform during activity. The right balance of macro and micronutrients may vary depending on your fitness level and the type of activity you perform. Still, it is important to get enough nutrition to maintain your health and optimize your performance.

Proper nutrition is imperative to maximize athletic performance. Without enough carbohydrates, proteins, and fats, athletes may feel sluggish and fatigued during a workout or ravenously hungry. Athletes may also need to focus on specific vitamins and minerals for fitness performance, such as iron, vitamin D, and zinc.

Nutrition for physical activity is highly individualized. It is often helpful to consult with a sports dietitian to review your individual needs and make specific recommendations for your body and activity level.

Evidence Shows Proper Nutrition Supports Activity

While we frequently think about the health benefits of nutrition and physical activity separately, there is evidence that integrating both nutrition and physical activity produces greater benefits than focusing on one or the other.

Additionally, research shows that exercise informs food choices, and individuals who exercise may make more nutritious choices. Nutrition may also support muscle recovery by reducing inflammation. One study showed that individuals who were more physically active and had higher antioxidant intake had lower levels of systemic inflammation.

The Importance of Balance and Timing of Macronutrients

Consuming adequate amounts of macronutrients—carbohydrates, protein, and fat—to fuel our bodies is imperative for optimal exercise performance.

• Carbohydrates are our bodies' preferred source of fuel. They give us the energy we need to go about our day and maximize workouts and athletic performance.
• Protein is important for building muscle as well as the repair and recovery of bones, joints, and ligaments after a workout.
• Fat keeps us full and satisfied, helps cushion our bones and joints, and increases the absorption of fat-soluble vitamins A, E, D, and K.

When it comes to fueling for exercise, finding the right balance and optimal timing of macronutrients for your body is key. Physical performance and recovery after exercise are enhanced by consuming carbohydrates and protein.

One study looked at the effects of protein and carbohydrates on skeletal muscle regeneration given to athletes by shake or meal. 35 individuals ran 10 kilometers (6.2 miles) and then consumed either a protein/carbohydrate shake, a meal of white bread and sour milk cheese, or nothing. The study indicated that consumption of carbohydrates and protein by shake or food was preferable, as it reduced exercise-induced skeletal muscle damage and had anti-inflammatory effects.

A "superfood" is a term frequently used by the food industry to market a specific food as offering maximum nutritional benefits or being exceptionally nutrient-dense.

While some foods are more nutritious than others and may positively affect health, it is essential to note that no single food is responsible for optimal health or disease prevention.

If you are looking to increase the nutrient density of your diet, including some of the following nutritious foods is an excellent place to start. These foods, including leafy greens, berries, eggs, sweet potato, and turmeric, contain antioxidants, complex carbohydrates, and protein and are beneficial for athletic performance.

Dark Leafy Greens

Dark green leafy vegetables are packed with important nutrients such as folate, zinc, calcium, magnesium, iron, vitamin C, and fiber. Eating leafy greens, such as spinach, kale, collard greens, and swiss chard, is shown to increase muscle function in men and women engaging in physical activity.

Additionally, the nitrates in leafy greens convert to nitric oxide, opening blood vessels and improving blood flow during exercise. You can incorporate dark leafy green vegetables into your diet by making kale salads, sautéing spinach into eggs for breakfast, or blending them into a smoothie.

Berries are known for their powerful antioxidant properties, making them an important part of an athlete's diet. Exercise causes oxidative stress, which results in the production of free radicals, muscle damage, and fatigue. Including antioxidants in the diet may help enhance athletic performance by decreasing muscle damage and inflammation.

Top a yogurt parfait with blueberries, blend strawberries into a smoothie, or add raspberries or blackberries into a salad to get an antioxidant punch.

Eggs, including the yolks, are rich in B vitamins, choline, iron, antioxidants, and high-quality protein, which is important for muscle recovery and repair. The protein in eggs is considered to have high bioavailability, meaning it is easily digested and efficiently metabolized by the body.

Additionally, eggs contain fatty acids that are important for heart health as well as vitamins and minerals that help with cell growth and tissue repair. Eggs are an easy and quick breakfast, scrambled with veggies or hardboiled for grab and go.

Sweet Potato

Sweet potatoes are a root vegetable packed with potassium, fiber, and vitamins A and C. They are an excellent source of complex carbohydrates needed by athletes for fuel. Getting enough potassium also reduces fatigue, muscle cramps, and the feeling of weakness.

Sweet potatoes can be incorporated into your diet in several ways. Top a baked sweet potato with Greek yogurt and almond butter for breakfast, roast wedges, add them to a salad, or bake until crispy and enjoy as sweet potato fries with a burger.

Turmeric is a bright yellow spice, originally from India, used for cooking and medicinal benefits. It is best known for its antioxidant and anti-inflammatory effect and may play a role in preventing chronic diseases such as cancer, heart disease, and diabetes.

Turmeric is also a more recent focus of post-exercise recovery research. Evidence suggests that individuals who use turmeric after a workout experience reduced muscle pain and tenderness, reduced muscle damage, and decreased inflammatory markers.

Incorporate turmeric into your routine by sprinkling the spice on roasted vegetables, adding it to a curry , or making golden milk . Turmeric is also available in supplement form .

Adequate hydration is imperative to overall health and exercise performance. We all lose water through normal bodily functions, such as breathing, digestion, and sweating. Athletes need to replace additional water and electrolytes lost through exertion during exercise.

Dehydration can lead to cardiovascular strain, altered metabolic function, and increased body temperature. Individuals also lose sodium, potassium, calcium, and magnesium with sweat. To avoid dehydration, it is important to ensure you are drinking before, during, and after exercise to maintain adequate hydration levels.

Whether you're training to run one mile, your first 5K, or a marathon, start with small and realistic nutrition and hydration goals. Trying to overhaul your entire diet at one time can feel overwhelming, and it is likely unsustainable. Small goals are more sustainable and, therefore, more beneficial in the long term.

If you feel your hydration is lacking, try investing in a fun water bottle . Flavor your water with fresh fruit or liquid beverage enhancers if you like your water to have a taste. Try adding one extra glass of water to your day.

Looking to include more antioxidants in your diet? Try adding one fruit and one vegetable to your meals each day. Pick one new nutrient-dense food and add it to your weekly meal plan. Add one each week, and soon enough, you will have greatly increased the variety of vitamins and minerals in your diet.

A Word From Verywell

Sustainable, enjoyable nutrition habits are key to reaching your goals. It can be tempting to follow a fad diet or social media trend, but frequently these diets are restrictive and unsustainable. If you have questions or concerns or want individualized nutrition recommendations, seek advice from a registered dietitian .

S.M.A.R.T goals stand for Specific, Measurable, Achievable, Realistic, and Time-Bound. S.M.A.R.T goals serve as small, doable action steps to help you change your behavior and achieve your goal. An example of a S.M.A.R.T goal is "I will include one vegetable at dinner 3 nights this week."

Nutrition impacts so much of our ability to function, from our physical to mental wellbeing. Incorporating nutritious foods in your diet and eating a balance of carbohydrates, protein, and fat appropriate for your needs can positively affect your everyday life and fitness performance.

Nutrition needs vary based on many factors, including age and life stage. As we age, we may experience some changes, such as bone loss, loss of muscle mass, thinner skin, and less stomach acid. Some of these changes may make you prone to nutrient deficiencies and you may need to increase your intake of certain foods or add supplements. Aging also causes a slower metabolism and decreased calorie needs.

Several factors affect your nutritional needs, including genetics, health status, environment , gut health, stage of life, fitness and activity level, and medications. Speak with a registered dietitian to better estimate your individual nutritional needs.

Koehler K, Drenowatz C. Integrated Role of Nutrition and Physical Activity for Lifelong Health .  Nutrients . 2019;11(7):1437. doi:10.3390/nu11071437

Gustafson CR, Rakhmatullaeva N, Beckford SE, Ammachathram A, Cristobal A, Koehler K. Exercise and the Timing of Snack Choice: Healthy Snack Choice is Reduced in the Post-Exercise State .  Nutrients . 2018;10(12):1941. doi:10.3390/nu10121941

Draganidis D, Jamurtas AZ, Stampoulis T, et al. Disparate Habitual Physical Activity and Dietary Intake Profiles of Elderly Men with Low and Elevated Systemic Inflammation .  Nutrients . 2018;10(5):566. doi:10.3390/nu10050566

Vitale K, Getzin A. Nutrition and Supplement Update for the Endurance Athlete: Review and Recommendations .  Nutrients . 2019;11(6):1289. doi:10.3390/nu11061289

Isenmann E, Blume F, Bizjak DA, et al. Comparison of Pro-Regenerative Effects of Carbohydrates and Protein Administrated by Shake and Non-Macro-Nutrient Matched Food Items on the Skeletal Muscle after Acute Endurance Exercise .  Nutrients . 2019;11(4):744. Published 2019 Mar 30. doi:10.3390/nu11040744

Sim M, Blekkenhorst LC, Bondonno NP, et al. Dietary Nitrate Intake Is Positively Associated with Muscle Function in Men and Women Independent of Physical Activity Levels .  J Nutr . 2021;151(5):1222-1230. doi:10.1093/jn/nxaa415

Hoon MW, Johnson NA, Chapman PG, Burke LM. The effect of nitrate supplementation on exercise performance in healthy individuals: a systematic review and meta-analysis.   Int J Sport Nutr Exerc Metab . 2013;23(5):522-532. doi:10.1123/ijsnem.23.5.522

Mason SA, Trewin AJ, Parker L, Wadley GD. Antioxidant supplements and endurance exercise: Current evidence and mechanistic insights .  Redox Biol . 2020;35:101471. doi:10.1016/j.redox.2020.101471

López Sobaler AM, Aparicio Vizuete A, Ortega RM. Papel del huevo en la dieta de deportistas y personas físicamente activas [ Role of the egg in the diet of athletes and physically active people ].  Nutr Hosp . 2017;34(Suppl 4):31-35. doi:10.1016/j.redox.2020.101471

Lindinger MI, Cairns SP. Regulation of muscle potassium: exercise performance, fatigue and health implications .  Eur J Appl Physiol . 2021;121(3):721-748. doi:10.1007/s00421-020-04546-8

Mahmood K, Zia KM, Zuber M, Salman M, Anjum MN. Recent developments in curcumin and curcumin based polymeric materials for biomedical applications: A review .  Int J Biol Macromol . 2015;81:877-890. doi:10.1016/j.ijbiomac.2015.09.026

Campbell MS, Carlini NA, Fleenor BS. Influence of curcumin on performance and post-exercise recovery .  Crit Rev Food Sci Nutr . 2021;61(7):1152-1162. doi:0.1080/10408398.2020.1754754

Thomas DT, Erdman KA, Burke LM. American College of Sports Medicine Joint Position Statement. Nutrition and Athletic Performance [published correction appears in Med Sci Sports Exerc . 2017 Jan;49(1):222].  Med Sci Sports Exerc . 2016;48(3):543-568. doi:10.1249/MSS.0000000000000852

Sipponen P, Maaroos HI. Chronic gastritis .  Scand J Gastroenterol . 2015;50(6):657-667. doi:10.3109/00365521.2015.1019918

The Journal of Clinical Endocrinology & Metabolism,  Water-Induced Thermogenesis , Michael Boschmann, 7/2/13

• Di Noia J.  Defining Powerhouse Fruits and Vegetables: A Nutrient Density Approach .  Prev Chronic Dis . 2014;11:130390.
• Emilio Ros,  Health Benefits of Nut Consumption , National Institutes of Health, 2010

By Darla Leal Darla Leal is a Master Fitness Trainer, freelance writer, and the creator of Stay Healthy Fitness, where she embraces a "fit-over-55" lifestyle.

Physical Education

Physical education is the foundation of a Comprehensive School Physical Activity Program. 1, 2 It is an academic subject characterized by a planned, sequential K–12 curriculum (course of study) that is based on the national standards for physical education. 2–4 Physical education provides cognitive content and instruction designed to develop motor skills, knowledge, and behaviors for physical activity and physical fitness. 2–4 Supporting schools to establish physical education daily can provide students with the ability and confidence to be physically active for a lifetime. 2–4

There are many benefits of physical education in schools. When students get physical education, they can 5-7 :

• Increase their level of physical activity.
• Improve their grades and standardized test scores.
• Stay on-task in the classroom.

Increased time spent in physical education does not negatively affect students’ academic achievement.

Strengthen Physical Education in Schools [PDF – 437 KB] —This data brief defines physical education, provides a snapshot of current physical education practices in the United States, and highlights ways to improve physical education through national guidance and practical strategies and resources. This was developed by Springboard to Active Schools in collaboration with CDC.

Secular Changes in Physical Education Attendance Among U.S. High School Students, YRBS 1991–2013

The Secular Changes in Physical Education Attendance Among U.S. High School Students report [PDF – 3 MB] explains the secular changes (long-term trends) in physical education attendance among US high school students over the past two decades. Between 1991 and 2013, US high school students’ participation in school-based physical education classes remained stable, but at a level much lower than the national recommendation of daily physical education. In order to maximize the benefits of physical education, the adoption of policies and programs aimed at increasing participation in physical education among all US students should be prioritized. Download the report for detailed, nationwide findings.

Physical Education Analysis Tool (PECAT)

The  Physical Education Curriculum Analysis Tool (PECAT) [PDF – 6 MB] is a self-assessment and planning guide developed by CDC. It is designed to help school districts and schools conduct clear, complete, and consistent analyses of physical education curricula, based upon national physical education standards.

Visit our PECAT page  to learn more about how schools can use this tool.

• CDC Monitoring Student Fitness Levels1 [PDF – 1.64 MB]
• CDC Ideas for Parents: Physical Education [PDF – 2 MB]
• SHAPE America: The Essential Components of Physical Education (2015) [PDF – 391 KB]
• SHAPE America: Appropriate Instructional Practice Guidelines for Elementary, Middle School, and High School Physical Education [PDF – 675 KB]
• SHAPE America: National Standards and Grade-Level Outcomes for K–12 Physical Education 2014
• SHAPE America: National Standards for K–12 Physical Education (2013)
• SHAPE America Resources
• Youth Compendium of Physical Activities for Physical Education Teachers (2018) [PDF – 145 KB]
• Social Emotional Learning Policies and Physical Education
• Centers for Disease Control and Prevention. A Guide for Developing Comprehensive School Physical Activity Programs . Atlanta, GA: Centers for Disease Control and Prevention, US Department of Health and Human Services; 2013.
• Centers for Disease Control and Prevention. School health guidelines to promote healthy eating and physical activity. MMWR . 2011;60(RR05):1–76.
• Institute of Medicine. Educating the Student Body: Taking Physical Activity and Physical Education to School . Washington, DC: The National Academies Press; 2013. Retrieved from  http://books.nap.edu/openbook.php?record_id=18314&page=R1 .
• SHAPE America. T he Essential Components of Physical Education . Reston, VA: SHAPE America; 2015. Retrieved from   http://www.shapeamerica.org/upload/TheEssentialComponentsOfPhysicalEducation.pdf  [PDF – 392 KB].
• Centers for Disease Control and Prevention. The Association Between School-Based Physical Activity, Including Physical Education, and Academic Performance . Atlanta, GA; Centers for Disease Control and Prevention, US Department of Health and Human Services; 2010.
• Centers for Disease Control and Prevention. Health and Academic Achievement. Atlanta: US Department of Health and Human Services; 2014.
• Michael SL, Merlo C, Basch C, et al. Critical connections: health and academics . Journal of School Health . 2015;85(11):740–758.

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How to Integrate Nutrition & Literacy into PE: Classics with Content

Our profession’s challenge to find balance between content rich activities and keeping students active has produced great strategies for blending content throughout student learning to provide more effective physical education. The goal of this blog is to share how the USDA’s Choose MyPlate website can enhance classic game activities by integrating nutrition in PE using the ‘10 tips’ Series.

Classic games such as tag, pin knockdown and bowling became revitalized when I began integrating the MyPlate content. Once pin knockdown was enhanced using colored pins to represent food groups and tag games could represent the balance between “energy in” (food consumed) and “energy out” (exercise) students became more engaged and this provided valuable talking points at the end of lessons that extended the bond across the psychomotor, cognitive and affective domains. It was the priceless trifecta I was looking for and has challenged me to continue to enhance other areas of my instruction.

Before I move into specific examples, here are 3 tips to help you get started with blending content into activities if you haven’t already done so:

1) Balance : Finding the balance between how much talking and moving is the first barrier to overcome. Realize effective physical education requires students to talk and interact with one another to help process learning. Challenge yourself to plan for these teachable moments and begin to find a balance that works for you and your students.

2) Purposeful Progressions : Analyze your curriculum and identify activity or skill progressions that may lend themselves well to integrating content progressions such as nutrition.

3) Start Small & Keep It Simple : Once you decide when, how and what to do…you just gotta GO FOR IT! Try it, and then try it again and again. It gets easier and better each time.

FREE Resource : One valuable (and FREE) resource that will enhance your current curriculum and/or offer a starting point if you have no formal curriculum is: C hoose My Plate . Here I use the 10 Tips series and the .pdf handout of the MyPlate as a student game board.

The MyPlate 10 Tips Nutrition Education Series offers one-page, reader friendly handouts with ‘10 tips’ on nutrition based topics. From “Add More Vegetables to Your Day”, to “Snack Tips”, to “Build a Healthy Meal”, to “Be an Active Family” there are over 30 choices. An educator could easily have a theme for each week of the year and have great nutrition talking points that can be integrated throughout the week’s activities and sent home with students or put in newsletters to communicate with families and promote health literacy. The information can be adapted for use in most any activity in my class.

Here are three examples of how I have integrated the ‘10 tips’ handouts into activity. To prepare for these, take a 10-tips handout and cut each tip out to make “tickets” then place them in team envelopes or mix them together depending upon the activity (See ticket sample and detailed game ideas on my website ). I have put the food group tips into a word document and will share them to help get your started.

Activity #1: “My Plate in Motion” Bowling . After students knock down certain colored pins, or combination of pins, or for a strike/spare (whichever situation) they collect a tip from their team envelope or the food bank bucket (where a mix of tickets is located).  You can use the food group themed tips to have students build plates or collect all 10 tips from the envelope provided. You can do this style of activity with any skill development activity such as shooting in basketball or hockey .

Activity #2: “My Plate in Motion” Fitness . Set up fitness stations. After students complete a station they can earn a tip ticket for their team and take it back to their “home” location (hulahoop) and then go back out to exercise and earn more tips. Use the same strategy to build a plate or collect all 10 of one theme.

Activity #3: “My Plate in Motion” Relays & Tag . Take any standard relay or tag game and integrate the ‘10 tips’ tickets where students work together to collect all 10 tickets on a certain topic or theme.

Ultimately, I want to encourage our profession to keep students moving, having fun, and learning purposeful content. Use the Choose MyPlate  resource as a springboard to promote health literacy and nutrition in PE in a simple and fun manner as you continue or begin the journey of integrating content into your effective physical education program. If you are looking for some great ready-to-go activities, d on’t forget to check out these  fun  and  easy-to-use  Nutrition-Themed Games  from Gopher!

Continue the conversation: What resources or tips have you used to help blend purposeful content into your activity and instruction?

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School health and nutrition

Good health and nutrition are foundations for learning and a crucial investment for more sustainable, inclusive and peaceful futures – they can improve education outcomes, empower learners to thrive and promote inclusion and equity in education and health.

What is the state of school health and nutrition around the world?

The good news is that:

• 9 in 10 countries globally invest in school health and nutrition programmes.
• More than 100 countries have school vaccination programmes.
• One in two primary school children receives school meals
• Almost every country includes education for health and well-being in its curriculum.

And yet many children, in particular girls, are missing out especially in the poorest countries.

• 73 million of the most marginalized children are not reached by school feeding, undermining their ability to benefit from education.
• Over 246 million learners experience violence in and around school every year.
• 1 in 3 schools do not have basic drinking water and adequate sanitation.

Developed by UNESCO and five UN partners (UNICEF, WFP, FAO, GPE, and WHO), in collaboration with the World Bank, the Research Consortium for School Health and Nutrition and the UN-Nutrition Secretariat,  Ready to learn and thrive  takes stock of countries’ policies and programmes around health and nutrition, and underscores school health and nutrition as an effective and affordable way to ensure learners learn and thrive throughout their education pathway and beyond. 

What does health and nutrition mean for learners and schools?

School health and nutrition is about investing both in learners’ education  and  their health, with benefits extending to homes and communities. Ensuring the health and well-being of learners is one of the most transformative ways to improve education outcomes, promote inclusion and equity and to rebuild the education system, especially following the COVID-19 pandemic.

The report shows that healthy, well-nourished and happy children and adolescents learn better and are more likely to lead healthy and fulfilling lives. For example, learners are 50% less likely to skip school when the learning environment is free from violence; absenteeism is reduced in low-income countries when promoting handwashing in particular for girls during menstruation when water, sanitation and hygiene is improved, and enrolment rates increase when school meals are provided to learners.

What are some of the key challenges?

Despite significant progress on school health and nutrition, more work must be done to ensure that the programmes in place are comprehensive, meet the needs of  all  learners and can be sustained. Many children are still missing out, especially in the poorest countries and most marginalized communities.

While the multisectoral nature of school health and nutrition is a strength, it can also lead to diffused action and scattered interventions. More attention needs to be paid to the quality of progammes, the synergies with existing efforts and the monitoring and evaluating of actions’ delivery and impact.

As the world is facing a global food crisis and struggling with the devastating effects of the COVID-19 pandemic, school health and nutrition must be integral to the daily mission of education systems across the globe.

What can we do about it?

To transform education and the lives of children and adolescents, this publication urges governments and development partners to put learners’ health and well-being at the core of the education agenda and to improve the quality and reach of school health and nutrition programmes.

We need comprehensive policies and programmes that address  all  learners’ needs holistically, are relevant and responsive to contexts and evolving needs, coordinated across sectors and sustained by increased policy and financial commitments.

There are many ways in which schools can promote physical and mental health and well-being. This starts by including health and well-being in curriculum, providing nutritious school meals and ensuring access to health services. It also means ensuring that school environments are free from violence and conducive to good health, nutrition, development and learning. Greater efforts to engage learners and communities and to ensure school staff and teachers have the necessary knowledge, tools and support are also needed.

School health and nutrition actions are a cost-effective investment. They can help reach marginalized learners and advance inclusion and equity, while benefitting multiple sectors including education, health, social protection and agriculture.

How does UNESCO work to advance school health and nutrition?

At UNESCO, school health and nutrition are core parts of its education mandate. We know that children and youth learn better when they are happy, healthy and thriving in school. This means that their learning environment must feel safe, offer healthy meals and promote physical and mental health.

Guided by its  Strategy on education for health and well-being , UNESCO offers technical advice and resources, and fosters resilient and health-promoting education systems. The  Global Standards for Health-Promoting Schools  by UNESCO and WHO, for example, supports countries to adopt and institutionalize a holistic approach that promotes the physical and mental health and well-being of all learners.

The COVID-19 pandemic has demonstrated the interlinkages between education and health and the urgent need to work together across sectors. This is especially the case around the mental health of learners post-COVID. In Chile for example, UNESCO provided technical advice to the  Seamos Comunidad  programme which addresses the effects of the pandemic through a focus on improved relations and infrastructures, and better mental health and learning in school.

Through its work with governments, partners and civil society, UNESCO seeks to create and support education and school systems that foster a safe and healthy learning environment, enabling learners to thrive and get the most benefits out of their education. A series of guidance and tools were produced by UNESCO to help countries respond to  school violence and bullying ,  school-related gender-based violence , and other forms of violence in and around school.

School health and nutrition for every learner

Partner commitments

• Download  the global report  and the  highlights  from the report
• Social media pack
• Press release:  Educational achievement is hampered by lack of investment in health and nutrition
• GPE blog:  School health and nutrition are needed to unlock the potential of every child
• Read about a good practice in Malawi:  How Wezzie is inspiring her students to make healthy choices in school and life in Malawi

Transforming education: Putting learners’ health and well-being first

More resources

• UNESCO strategy on education for health and well-being
• Stepping up effective school health and nutrition: a partnership for healthy learners and brighter futures
• The journey towards comprehensive sexuality education: global status report
• UNESCO Health and education resource centre
• UNESCO’s work on education for health and well-being
• Ready to learn and thrive: Release of the report on school health and nutrition around the world , video of the launch webinar, 3 February 2023

Related items

• Health education
• Nutrition education
• See more add

Educating the Student Body: Taking Physical Activity and Physical Education to School (2013)

Chapter: 3 physical activity and physical education: relationship to growth, development, and health.

Physical Activity and Physical Education: Relationship to Growth, Development, and Health

Key Messages

•  Regular physical activity promotes growth and development and has multiple benefits for physical, mental, and psychosocial health that undoubtedly contribute to learning.

•  Specifically, physical activity reduces the risk for heart disease, diabetes mellitus, osteoporosis, high blood pressure, obesity, and metabolic syndrome; improves various other aspects of health and fitness, including aerobic capacity, muscle and bone strength, flexibility, insulin sensitivity, and lipid profiles; and reduces stress, anxiety, and depression.

•  Physical activity can improve mental health by decreasing and preventing conditions such as anxiety and depression, as well as improving mood and other aspects of well-being.

•  Physical activity programming specifically designed to do so can improve psychosocial outcomes such as self-concept, social behaviors, goal orientation, and most notably self-efficacy. These attributes in turn are important determinants of current and future participation in physical activity.

•  Sedentary behaviors such as sitting and television viewing contribute to health risks both because of and independently of their impact on physical activity.

•  Health-related behaviors and disease risk factors track from childhood to adulthood, indicating that early and ongoing opportunities for physical activity are needed for maximum health benefit.

•  To be effective, physical activity programming must align with the predictable developmental changes in children’s exercise capacity and motor skills, which affect the activities in which they can successfully engage.

•  Frequent bouts of physical activity throughout the day yield short-term benefits for mental and cognitive health while also providing opportunities to practice skills and building confidence that promotes ongoing engagement in physical activity.

•  Distinct types of physical activity address unique health concerns and contribute in distinct ways to children’s health, suggesting that a varied regimen including aerobic and resistance exercise, structured and unstructured opportunities, and both longer sessions and shorter bouts will likely confer the greatest benefit.

T he behaviors and traits of today’s children, along with their genetics, are determinants of their growth and development; their physical, mental, and psychosocial health; and their physical, cognitive, and academic performance. Technological advances of modern society have contributed to a sedentary lifestyle that has changed the phenotype of children from that of 20 years ago. Children today weigh more and have a higher body mass index (BMI) than their peers of just a generation earlier (Ogden et al., 2012). Behaviorally, most children fail to engage in vigorous- or moderate-intensity physical activity for the recommended 60 minutes or more each day, with as many as one-third reporting no physical activity in the preceding 5 days (CDC, 2012). This lack of participation in physical activity has contributed to a greater prevalence of pediatric obesity, a decrease in fitness (e.g., flexibility, muscular strength, cardiorespiratory capacity), and a greater risk for disease (Boreham and Riddoch, 2001; Eisenmann, 2003; Malina, 2007; Steele et al., 2008). (See Box 3-1 for an overview of the relationship between physical activity and physical fitness.)

Physical Activity and Physical Fitness

As noted in Chapter 1 (see the box titled “Key Terms Used in This Report” on p. 17), physical activity, a behavior, is defined as bodily movement that increases energy expenditure, whereas fitness is a physiologic trait, commonly defined in terms of cardiorespiratory capacity (e.g., maximal oxygen consumption), although other components of fitness have been defined (IOM, 2012b). Exercise, a subset of physical activity, is “planned, structured and repetitive” (Carpersen et al., 1985, p. 128) and designed to target a particular outcome, for example, cardiorespiratory capacity or another component of fitness. Physical education provides opportunities for developmentally appropriate physical activity, usually structured to promote motor skill development, fitness, and health.

The relationship between physical activity and physical fitness is complex and bidirectional. Numerous studies have shown a significant relationship between physical activity and cardiorespiratory fitness, which may mean that physical activity improves fitness or that physically fit individuals choose to engage in physical activity more than their less fit peers, or both. Experimental studies have shown that exercise training improves fitness (Malina et al., 2004), although the response is variable and clearly influenced by genetics (Bouchard, 2012), and physical activity and fitness are independently related to health and academic performance (see the figure below).

Conceptual framework illustrating relationships among physical activity, physical fitness, health, and academic performance.

While more can always be learned, the evidence for the health benefits of physical activity is irrefutable (HHS, 1996, 2008). Adults engaged in regular physical activity have lower rates of chronic disease (e.g., coronary heart disease, cardiovascular disease, type 2 diabetes, hypertension, osteoporosis, and some cancers) and are less likely to die prematurely (HHS, 1996, 2008; Bauman, 2004). And while the ill effects of chronic disease are manifested mainly in adults, it is increasingly better understood that the development of these conditions starts in childhood and adolescence (Hallal et al., 2006; Cook et al., 2009; Halfon et al., 2012). It appears evident, then, that promotion of health-enhancing behaviors must also start early in life. Indeed, growing evidence points to long-term effects of child and adolescent physical activity on adult morbidity and mortality in addition to its more immediate effects (Hallal et al., 2006) (see Figure 3-1 ).

Evidence for both direct and indirect health effects of physical activity has been reported (Hallal et al., 2006), and the need for ongoing participation in physical activity to stimulate and maintain the chronic adaptations that underlie those benefits is well documented. To understand the relation-

FIGURE 3-1 Conceptual model of how physical activity in childhood and adolescence is beneficial to health. Physical activity has both immediate and long-term health benefits: (a) Physical activity tends to track; early physical activity is associated with physical activity in subsequent life stages. (b) Physical activity reduces morbidity risk in childhood and adolescence. (c) Physical activity may be important in treating and slowing some diseases in children and adolescents. (d) Early physical activity influences future morbidity (e.g., physical activity in childhood and adolescence may reduce fracture risk later in life). SOURCE: Adapted from Hallal et al., 2006.

ship of physical activity and aerobic fitness to health during childhood, it is important first to recognize the developmental changes that occur throughout maturation. During the early stages of adolescence, for example, participation in physical activity and corresponding physical fitness begin to decline (Duncan et al., 2007). Such differences across stages of development highlight the importance of examining the effects of growth and maturation on physical and cognitive health. Accordingly, this chapter reviews how physical activity may influence developmental processes and other aspects of somatic growth and maturation. A complete review of the effects of physical activity on all tissues and systems is beyond the scope of this report. Rather, the focus is on components of body composition and systems that underlie engagement in physical activity, physical fitness, and chronic disease risk and that in turn influence other aspects of health and academic performance (discussed in Chapter 4 ). Addressed in turn is the relationship between physical activity and physical, psychosocial, and mental health. Structural and functional brain maturation and how physical activity may influence those developmental processes and cognitive health are also reviewed in Chapter 4 .

PHYSICAL HEALTH

This section reviews what is known about the relationship between physical activity and (1) somatic growth, development, and function and (2) health- and performance-related fitness.

Somatic Growth, Development, and Function

Growth occurs through a complex, organized process characterized by predictable developmental stages and events. Although all individuals follow the same general course, growth and maturation rates vary widely among individuals. Just as it is unrealistic to expect all children at the same age to achieve the same academic level, it is unrealistic to expect children at the same age to have the same physical development, motor skills, and physical capacity. Regular physical activity does not alter the process of growth and development. Rather, developmental stage is a significant determinant of motor skills, physical capacity, and the adaptation to activity that is reasonable to expect (see Box 3-2 ).

Developmental Stages

Postnatal growth is commonly divided into three or four age periods. Infancy spans the first year of life. Childhood extends from the end of infancy to the start of adolescence and is often divided into early child-

Growth, Development, and Maturation

Growth is the normal process of increase in size as a result of accretion of tissues characteristic of the organism; growth is the dominant biological activity for most of the first two decades of life. Changes in size are the outcome of an increase in cell number (hyperplasia), an increase in cell size (hypertrophy), and an increase in intercellular substances (accretion).

Development

Encompassing growth and maturation, development denotes a broader concept; when used in a biological context, development refers to differentiation and specialization of stem cells into different cell types, tissues, organs, and functional units. Development continues as different systems become functionally refined. Development also refers to the acquisition and refinement of behavior relating to competence in a variety of interrelated domains, such as motor competence and social, emotional, and cognitive competence.

Maturation is the timing and tempo of progress toward the mature state and varies considerably among individuals; variation in progress toward the mature state over time implies variation in the rate of change. Two children may be the same size but at different points on the path to adult size or maturity.

hood, which includes the preschool years, and middle childhood, which includes the elementary school years, into the 5th or 6th grade. Adolescence is more difficult to define because of variation in its onset and termination, although it is commonly defined as between 10 and 18 years of age (WHO, 1986). The rapid growth and development of infancy continue during early childhood, although at a decelerating rate, whereas middle childhood is a period of slower, steady growth and maturation. Differences between boys and girls are relatively small until adolescence, which is marked by accelerated growth and attainment of sexual maturity (Tanner, 1962).

Across developmental stages, neurological development and control of movement advance in cephalocaudal and proximodistal directions; that is, they advance “head to toe” (cephalocaudal) and “midline to periphery” (proximodistal), while predictable changes in body proportions also occur. For example, the head accounts for 25 percent of recumbent length in an infant and only 15 percent of adult height, while the legs account for 38 percent of recumbent length at birth and 50 percent of adult height. These changes in body proportions occur because body parts grow at different rates. From birth to adulthood, as the head doubles in size, the trunk triples in length, and arm and leg lengths quadruple.

Coincident with these changes in body proportions, and in part because of them, the capacity to perform various motor tasks develops in a predictable fashion. For example, running speed increases are consistent with the increase in leg length. Neurological development also determines skill progression. Young children, for example, when thrown a ball, catch it within the midline of the body and do not attempt to catch it outside the midline or to either side of the body. As proximodistal development proceeds, children are better able to perform tasks outside their midline, and by adolescence they are able to maneuver their bodies in a coordinated way to catch objects outside the midline with little effort.

Physically active and inactive children progress through identical stages. Providing opportunities for young children to be physically active is important not to affect the stages but to ensure adequate opportunity for skill development. Sound physical education curricula are based on an understanding of growth patterns and developmental stages and are critical to provide appropriate movement experiences that promote motor skill development (Clark, 2005). The mastery of fundamental motor skills is strongly related to physical activity in children and adolescents (Lubans et al., 2010) and in turn may contribute to physical, social, and cognitive development. Mastering fundamental motor skills also is critical to fostering physical activity because these skills serve as the foundation for more advanced and sport-specific movement (Clark and Metcalfe, 2002; Hands et al., 2009; Robinson and Goodway, 2009; Lubans et al., 2010). Physical activity programs, such as physical education, should be based on developmentally appropriate motor activities to foster self-efficacy and enjoyment and encourage ongoing participation in physical activity.

Biological Maturation

Maturation is the process of attaining the fully adult state. In growth studies, maturity is typically assessed as skeletal, somatic, or sexual. The same hormones regulate skeletal, somatic, and sexual maturation during adolescence, so it is reasonable to expect the effect of physical activity on

these indicators of maturity to be similar. Skeletal maturity is typically assessed from radiographs of the bones in the hand and wrist; it is not influenced by habitual physical activity. Similarly, age at peak height velocity (the most rapid change in height), an indicator of somatic maturity, is not affected by physical activity, nor is the magnitude of peak height velocity, which is well within the usual range in both active and inactive youth. Discussions of the effects of physical activity on sexual maturation more often focus on females than males and, in particular, on age at menarche (first menses). While some data suggest an association between later menarche and habitual physical activity (Merzenich et al., 1993), most of these data come from retrospective studies of athletes (Clapp and Little, 1995). Whether regular sports training at young ages before menarche “delays” menarche (later average age of menarche) remains unclear. While menarche occurs later in females who participate in some sports, the available data do not support a causal relationship between habitual physical activity and later menarche.

Puberty is the developmental period that represents the beginning of sexual maturation. It is marked by the appearance of secondary sex characteristics and their underlying hormonal changes, with accompanying sex differences in linear growth and body mass and composition. The timing of puberty varies, beginning as early as age 8 in girls and age 9 in boys in the United States and as late as ages 13-15 (NRC/IOM, 1999). Recent research suggests that the onset of puberty is occurring earlier in girls today compared with the previous generation, and there is speculation that increased adiposity may be a cause (Bau et al., 2009; Rosenfield et al., 2009). Conversely, some data suggest that excess adiposity in boys contributes to delayed sexual maturation (Lee et al., 2010). Pubescence, the earliest period of adolescence, generally occurs about 2 years in advance of sexual maturity. Typically, individuals are in the secondary school years during this period, which is a time of decline in habitual physical activity, especially in girls. Physical activity trends are influenced by the development of secondary sex characteristics and other physical changes that occur during the adolescent growth spurt, as well as by societal and cultural factors. Research suggests that physical inactivity during adolescence carries over into adulthood (Malina, 2001a,b; CDC, 2006).

It is critical that adolescents be offered appropriate physical activity programs that take into account the physical and sociocultural changes they are experiencing so they will be inspired to engage in physical activity for a lifetime. As discussed below, adequate physical activity during puberty may be especially important for optimal bone development and prevention of excess adiposity, as puberty is a critical developmental period for both the skeleton and the adipose organ.

Adolescence is the transitional period between childhood and adulthood. The adolescent growth spurt, roughly 3 years of rapid growth, occurs early in this period. An accelerated increase in stature is a hallmark, with about 20 percent of adult stature being attained during this period. Along with the rapid increase in height, other changes in body proportions occur that have important implications for sports and other types of activities offered in physical education and physical activity programs. As boys and girls advance through puberty, for example, biacromial breadth (shoulder width) increases more in boys than in girls, while increases in bicristal breadth (hip width) are quite similar. Consequently, hip-shoulder width ratio, which is similar in boys and girls during childhood, decreases in adolescent boys while remaining relatively constant in girls (Malina et al., 2004). Ratios among leg length, trunk length, and stature also change during this period. Prior to adolescence, boys have longer trunks and shorter legs than girls (Haubenstricker and Sapp, 1980). In contrast, adolescent and adult females have shorter legs for the same height than males of equal stature. Body proportions, particularly skeletal dimensions, are unlikely to be influenced by physical activity; rather, body proportions influence performance success, fitness evaluation, and the types of activities in which a person may wish to engage. For example, there is evidence that leg length influences upright balance and speed (Haubenstricker and Sapp, 1980). Individuals who have shorter legs and broader pelvises are better at balancing tasks than those with longer legs and narrower pelvises, and longer legs are associated with faster running times (Dintiman et al., 1997). Also, longer arms and wider shoulders are advantageous in throwing tasks (Haubenstricker and Sapp, 1980), as well as in other activities in which the arms are used as levers. According to Haubenstricker and Sapp (1980), approximately 25 percent of engagement in movement-related activities can be attributed to body size and structure.

Motor Development

Motor development depends on the interaction of experience (e.g., practice, instruction, appropriate equipment) with an individual’s physical, cognitive, and psychosocial status and proceeds in a predictable fashion across developmental periods. Clark and Metcalfe (2002) provide an eloquent metaphor—“the mountain of motor development”—to aid in understanding the global changes seen in movement across the life span. Early movements, critical for an infant’s survival, are reflexive and dominated by biology, although environment contributes and helps shape reflexes. This initial reflexive period is followed quickly by the preadapted period , which begins when an infant’s movement behaviors are no longer reflexive and ends when the infant begins to apply basic movement skills (e.g.,

crawling, rolling, standing, and walking) that generally are accomplished before 12 months of age. The period of fundamental motor patterns occurs approximately between the ages of 1 and 7 years, when children begin to acquire basic fundamental movement skills (e.g., running, hopping, skipping, jumping, leaping, sliding, galloping, throwing, catching, kicking, dribbling, and striking). Practice and instruction are key to learning these skills, and a great deal of time in elementary school physical education is devoted to exploration of movement. Around age 7, during the so-called context-specific period of motor development, children begin to refine basic motor skills and combine them into more specific movement patterns, ultimately reaching what has been called skillfulness . Compensation , the final period of motor development, occurs at varying points across the life span when, as a result of aging, disease, injury, or other changes, it becomes necessary to modify movement.

While all children need not be “expert” in all movement skills, those who do not acquire the fundamental motor skills will likely experience difficulty in transitioning their movement repertoire into specific contexts and engagement in physical activity (Fisher et al., 2005; Barnett et al., 2009; Cliff et al., 2009; Robinson et al., 2012). A full movement repertoire is needed to engage in physical activities within and outside of the school setting. Thus, beyond contributing to levels of physical activity, physical education programs should aim to teach basic fundamental motor skills and their application to games, sports, and other physical activities, especially during the elementary years (i.e., the fundamental motor patterns and context-specific periods). At the same time, it is important to be mindful of the wide interindividual variation in the rate at which children develop motor skills, which is determined by their biological makeup, their rate of physical maturation, the extent and quality of their movement experiences, and their family and community environment.

An increasing amount of evidence suggests that people who feel competent in performing physical skills remain more active throughout their lives (Lubans et al., 2010). Conversely, those who are less skilled may be hesitant to display what they perceive as a shortcoming and so may opt out of activities requiring higher levels of motor competence (Stodden et al., 2008). Children who are less physically skillful tend to be less active than their skillful counterparts (Wrotniak et al., 2006; Williams et al., 2008; Robinson et al., 2012) and thus have a greater risk of overweight and obesity (Graf et al., 2004). Fundamental skills are the building blocks of more complex actions that are completed in sports, physical activities, and exercise settings. For example, throwing is a fundamental skill that is incorporated into the context-specific throw used in activities such as handball, softball, and water polo. Fundamental skills are of primary interest to both physical education teachers and coaches, and physical

education classes should be designed to challenge learners to develop their motor skills.

In 1998 the Centers for Disease Control and Prevention’s (CDC’s) Division of Nutrition and Physical Activity organized a workshop to determine future directions for research on physical activity. The workshop convened 21 experts from a wide range of academic disciplines. One recommendation resulting from the proceedings was for future research to describe the temporal relationship between motor development and physical activity (Fulton et al., 2001), signifying the importance of better understanding of the nature of the relationship between motor competence and physical activity. The assumption of this relationship is implied in multiple models of motor development (Seefeldt, 1980; Clark and Metcalfe, 2002; Stodden et al., 2008), which emphasize the importance of motor competence as a prerequisite for engagement in physical activity throughout the life span.

Two models that are commonly used to examine this relationship are Seefeldt’s (1980) hierarchical order of motor skills development and the dynamic association model of Stodden and colleagues (2008). Seefeldt proposed a hierarchical order of motor skills development that includes four levels: reflexes, fundamental motor skills, transitional motor skills (i.e., fundamental motor skills that are performed in various combinations and with variations and that are required to participate in entry-level organized sports, such as throwing for distance, throwing for accuracy, and/or catching a ball while in motion), and specific sports skills and dances. With improved transitional motor skills, children are able to master complex motor skills (e.g., those required for playing more complex sports such as football or basketball). At the end of this developmental period, children’s vision is fully mature. The progression through each level occurs through developmental stages as a combined result of growth, maturation, and experience. Seefeldt hypothesized the existence of a “proficiency barrier” between the fundamental and transitional levels of motor skills development. If children are able to achieve a level of competence above the proficiency barrier, they are more likely to continue to engage in physical activity throughout the life span that requires the use of fundamental motor skills. Conversely, less skilled children who do not exceed the proficiency barrier will be less likely to continue to engage in physical activity. Thus, it is assumed that “a confident and competent mover will be an active mover” (Clark, 2005, p. 44). For example, to engage successfully in a game of handball, baseball, cricket, or basketball at any age, it is important to reach a minimum level of competence in running, throwing, catching, and striking. The assumption of the existence of a relationship between motor competence and physical activity is at the “heart of our physical education programs” (Clark, 2005, p. 44). A thorough understanding of how this

relationship changes across developmental stages is crucial for curriculum development and delivery and teaching practices.

Lubans and colleagues (2010) recently examined the relationship between motor competence and health outcomes. They reviewed 21 studies identifying relationships between fundamental motor skills and self-worth, perceived physical competence, muscular and cardiorespiratory fitness, weight status, flexibility, physical activity, and sedentary behavior. Overall, the studies found a positive association between fundamental motor skills and physical activity in children and adolescents, as well as a positive relationship between fundamental motor skills and cardiorespiratory fitness. Other research findings support the hypothesis that the most physically active preschool-age (Fisher et al., 2005; Williams et al., 2008; Robinson et al., 2012), elementary school–age (Bouffard et al., 1996; Graf et al., 2004; Wrotniak et al., 2006; Hume et al., 2008; Lopes et al., 2011), and adolescent (Okely et al., 2001) youth are also the most skilled.

An advantage of the “proficiency barrier” hypothesis proposed by Seefeldt (1980) is its recognition that the relationship between motor competence and physical activity may not be linear. Rather, the hypothesis suggests that physical activity is influenced when a certain level of motor competence is not achieved and acknowledges that below the proficiency barrier, there is bound to be substantial variation in children’s motor competence and participation in physical activity. The proficiency barrier is located between the fundamental and transitional motor skills periods. The transition between these two levels of motor competence is expected to occur between the early and middle childhood years. Stodden and colleagues (2008) suggest that the relationship between motor competence and physical activity is dynamic and changes across time. In their model the “development of motor skill competence is a primary underlying mechanism that promotes engagement in physical activity” (p. 290).

The relationship between skills and physical activity is considered reciprocal. It is expected that as motor skills competence increases, physical activity participation also increases and that the increased participation feeds back into motor skills competence. The reciprocal relationship between motor skills competence and physical activity is weak during the early childhood years (ages 2-8) because of a variety of factors, including environmental conditions, parental influences, and previous experience in physical education programs (Stodden et al., 2008). Also, children at this age are less able to distinguish accurately between perceived physical competence and actual motor skills competence (Harter and Pike, 1984; Goodway and Rudisill, 1997; Robinson and Goodway, 2009; Robinson, 2011), and thus motor skills are not expected to strongly influence physical activ-

ity. The literature supports this hypothesis, as indicated by low to moderate correlations between motor skills competence and physical activity

in preschool (Sääkslahti et al., 1999; Williams et al., 2008; Cliff et al., 2009; Robinson and Goodway, 2009; Robinson, 2011) and early elementary school–age (Raudsepp and Päll, 2006; Hume et al., 2008; Morgan et al., 2008; Houwen et al., 2009; Ziviani et al., 2009; Lopes et al., 2011) children.

In older children, perceived competence is more closely related to actual motor skills competence. Older, low-skilled children are aware of their skills level and are more likely to perceive physical activity as difficult and challenging. Older children who are not equipped with the necessary skills to engage in physical activity that requires high levels of motor skills competence may not want to display their low competence publicly. As children transition into adolescence and early adulthood, the relationship between motor skills competence and physical activity may strengthen (Stodden et al., 2008). Investigators report moderate correlations between motor skills competence and physical activity in middle school–age children (Reed et al., 2004; Jaakkola et al., 2009). Okely and colleagues (2001) found that motor skills competence was significantly associated with participation in organized physical activity (i.e., regular and structured experiences related to physical activity) as measured by self-reports. A strength of the model of Stodden and colleagues (2008) is the inclusion of factors related to psychosocial health and development that may influence the relationship between motor skills competence and physical activity, contributing to the development and maintenance of obesity. Other studies have found that perceived competence plays a role in engagement in physical activity (Ferrer-Caja and Weiss, 2000; Sollerhed et al., 2008).

Motor skills competence is an important factor; however, it is only one of many factors that contribute to physical activity. For instance, three studies have reported negative correlations between girls’ motor competence and physical activity (Reed et al., 2004; Cliff et al., 2009; Ziviani et al., 2009), suggesting that sex may be another determining factor. A possible explanation for these findings is that since girls tend to be less active than boys, it may be more difficult to detect differences in physical activity levels between high- and low-skilled girls. It is also possible that out-of-school opportunities for physical activity are more likely to meet the interests of boys, which may at least partially explain sex differences in physical activity levels (Le Masurier et al., 2005). Previous research suggests that in general boys are more motor competent than girls (Graf et al., 2004; Barnett et al., 2009; Lopes et al., 2011) and that this trend, which is less apparent in early childhood, increases through adolescence (Thomas and French, 1985; Thomas and Thomas, 1988; Thomas, 1994), although one study reports that girls are more motor competent than boys (Cliff et al., 2009).

One component of motor competence is the performance of gross motor skills, which are typically classified into object control and

locomotor skills. Consistent evidence suggests that boys are more competent in object control skills, while girls are more competent in locomotor skills (McKenzie et al., 2004; Morgan et al., 2008; Barnett et al., 2009). In light of these sex differences, it is important to examine the relationships of object control and locomotor skills with physical activity separately for boys and girls. For boys, object control skills are more related to physical activity than are locomotor skills (Hume et al., 2008; Morgan et al., 2008; Williams et al., 2008; Cliff et al., 2009), whereas evidence suggests that the reverse is true for girls (McKenzie et al., 2002; Hume et al., 2008; Cliff et al., 2009; Jaakkola et al., 2009). Three studies report a significant relationship between balance and physical activity for girls but not boys (Reed et al., 2004; Ziviani et al., 2009). Cliff and colleagues (2009) suggest that object control and locomotor skills may be more related to boys’ and girls’ physical activity, respectively, because of the activity type in which each sex typically engages.

The relationship between motor competence and physical activity clearly is complex. It is quite likely that the relationship is dynamic and that motor competence increases the likelihood of participating in physical activity while at the same time engaging in physical activity provides opportunities to develop motor competence (Stodden et al., 2008). Despite some uncertainty, the literature does reinforce the important role of physical education in providing developmentally appropriate movement opportunities in the school environment. These opportunities are the only means of engaging a large population of children and youth and providing them with the tools and opportunities that foster health, development, and future physical activity.

Regular physical activity has no established effect on linear growth rate or ultimate height (Malina, 1994). Although some studies suggest small differences, factors other than physical activity, especially maturity, often are not well controlled. It is important to note that regular physical activity does not have a negative effect on stature, as has sometimes been suggested. Differences in height among children and adolescents participating in various sports are more likely due to the requirements of the sport, selection criteria, and interindividual variation in biological maturity than the effects of participation per se (Malina et al., 2004).

Body Weight

Although physical activity is inversely related to weight, correlations are generally low (~r –0.15), and differences in body weight between active and inactive boys and girls tend to be small (Mirwald and Bailey, 1986;

Saris et al., 1986; Beunen et al., 1992; Lohman et al., 2006;), except in very obese children and adolescents. Similarly, physique, as represented in somatotypes, does not appear to be significantly affected by physical activity during growth (Malina et al., 2004). In contrast, components of weight can be influenced by regular physical activity, especially when the mode and intensity of the activity are tailored to the desired outcome. Much of the available data in children and adolescents is based on BMI, a surrogate for composition, and indirect methods based on the two-compartment model of body composition in which body weight is divided into its fat-free and fat components (Going et al., 2012). While studies generally support that physical activity is associated with greater fat-free mass and lower body fat, distinguishing the effects of physical activity on fat-free mass from expected changes associated with growth and maturation is difficult, especially during adolescence, when both sexes have significant growth in fat-free mass. The application of methods based on the two-compartment model is fraught with errors, especially when the goal is to detect changes in fat-free mass, and no information is available from these methods regarding changes in the major tissue components of fat-free mass—muscle and skeletal tissue.

Muscle Skeletal muscle is the largest tissue mass in the body. It is the main energy-consuming tissue and provides the propulsive force for movement. Muscle represents about 23-25 percent of body weight at birth and about 40 percent in adults, although there is a wide range of “normal” (Malina, 1986, 1996). Postnatal muscle growth is explained largely by increases in cell size (hypertrophy) driving an increase in overall muscle mass. The increase in muscle mass with age is fairly linear from young childhood until puberty, with boys having a small but consistent advantage (Malina, 1969, 1986). The sex difference becomes magnified during and after puberty, driven primarily by gender-related differences in sex steroids. Muscle, as a percentage of body mass, increases from about 42 percent to 54 percent in boys between ages 5 and 11, whereas in girls it increases from about 40 percent to 45 percent between ages 5 and 13 and thereafter declines (Malina et al., 2004). It should be noted that absolute mass does not decline; rather, the relative decline reflects the increase in the percentage of weight that is fat in girls. At least part of the sex difference is due to differences in muscle development for different body regions (Tanner et al., 1981). The growth rate of arm muscle tissue during adolescence in males is approximately twice that in females, whereas the sex difference in the growth of muscle tissue in the leg is much smaller. The sex difference that develops during puberty persists into adulthood and is more apparent for the musculature of the upper extremities.

Sex-related differences in muscular development contribute to differences in physical performance. Muscle strength develops in proportion to the cross-sectional area of muscle, and growth curves for strength are essentially the same as those for muscle (Malina and Roche, 1983). Thus the sex difference in muscle strength is explained largely by differences in skeletal muscle mass rather than muscle quality or composition. Aerobic (endurance) exercise has little effect on enhancing muscle mass but does result in significant improvement in oxygen extraction and aerobic metabolism (Fournier et al., 1982). In contrast, numerous studies have shown that high-intensity resistance exercise induces muscle hypertrophy, with associated increases in muscle strength. In children and adolescents, strength training can increase muscle strength, power, and endurance. Multiple types of resistance training modalities have proven effective and safe (Bernhardt et al., 2001), and resistance exercise is now recommended for enhancing physical health and function (Behringer et al., 2010). These adaptations are due to muscle fiber hypertrophy and neural adaptations, with muscle hypertrophy playing a more important role in adolescents, especially in males. Prior to puberty, before the increase in anabolic sex steroid concentrations, neural adaptations explain much of the improvement in muscle function with exercise in both boys and girls.

Skeleton The skeleton is the permanent supportive framework of the body. It provides protection for vital organs and is the main mineral reservoir. Bone tissue constitutes most of the skeleton, accounting for 14-17 percent of body weight across the life span (Trotter and Peterson, 1970; Trotter and Hixon, 1974). Skeletal strength, which dictates fracture risk, is determined by both the material and structural properties of bone, both of which are dependent on mineral accrual. The relative mineral content of bone does not differ much among infants, children, adolescents, and adults, making up 63-65 percent of the dry, fat-free weight of the skeleton (Malina, 1996). As a fraction of weight, bone mineral (the ash weight of bone) represents about 2 percent of body weight in infants and about 4-5 percent of body weight in adults (Malina, 1996). Bone mineral content increases fairly linearly with age, with no sex difference during childhood. Girls have, on average, a slightly greater bone mineral content than boys in early adolescence, reflecting their earlier adolescent growth spurt. Boys have their growth spurt later than girls, and their bone mineral content continues to increase through late adolescence, ending with greater skeletal dimensions and bone mineral content (Mølgaard et al., 1997). The increase in total body bone mineral is explained by both increases in skeletal length and width and a small increase in bone mineral density (Malina et al., 2004).

Many studies have shown a positive effect of physical activity on intermediate markers of bone health, such as bone mineral content and density.

Active children and adolescents have greater bone mineral content and density than their less active peers, even after controlling for differences in height and muscle mass (Wang et al., 2004; Hind and Burrows, 2007; Tobias et al., 2007). Exercise interventions support the findings from observational studies showing beneficial effects on bone mineral content and density in exercise participants versus controls (Petit et al., 2002; Specker and Binkley, 2003), although the benefit is less than is suggested by cross-sectional studies comparing active versus inactive individuals (Bloomfield et al., 2004). The relationship between greater bone mineral density and bone strength is unclear, as bone strength cannot be measured directly in humans. Thus, whether the effects of physical activity on bone mineral density translate into similar benefits for fracture risk is uncertain (Karlsson, 2007). Animal studies have shown that loading causes small changes in bone mineral content and bone mineral density that result in large increases in bone strength, supporting the notion that physical activity probably affects the skeleton in a way that results in important gains in bone strength (Umemura et al., 1997). The relatively recent application of peripheral quantitative computed tomography for estimating bone strength in youth has also provided some results suggesting an increase in bone strength with greater than usual physical activity (Sardinha et al., 2008; Farr et al., 2011).

The intensity of exercise appears to be a key determinant of the osteogenic response (Turner and Robling, 2003). Bone tissue, like other tissues, accommodates to usual daily activities. Thus, activities such as walking have a modest effect at best, since even relatively inactive individuals take many steps (>1,000) per day. Activities generating greater muscle force on bone, such as resistance exercise, and “impact” activities with greater than ordinary ground reaction forces (e.g., hopping, skipping, jumping, gymnastics) promote increased mineralization and modeling (Bloomfield et al., 2004; Farr et al., 2011). Far fewer randomized controlled trials (RCTs) examining this relationship have been conducted in children than in adults, and there is little evidence on dose response to show how the type of exercise interacts with frequency, intensity, and duration. Taken together, however, the available evidence supports beneficial effects of physical activity in promoting bone development (Bailey et al., 1996; Modlesky and Lewis, 2002).

Physical activity may reduce osteoporosis-related fracture risk by increasing bone mineral accrual during development; by enhancing bone strength; and by reducing the risk of falls by improving muscle strength, flexibility, coordination, and balance (Bloomfield et al., 2004). Early puberty is a key developmental period. Approximately 26 percent of the mineral content in the adult skeleton is accrued during the 2 years around the time of peak height velocity (Bailey et al., 2000). This amount of mineral accrual represents approximately the same amount of bone mineral

that most people will lose in their entire adult lives (Arlot et al., 1997). The increase in mineral contributes to increased bone strength. Mineral is accrued on the periosteal surface of bone, such that the bone grows wider. Increased bone width, independent of the increased mineral mass, also contributes to greater bone strength. Indeed, an increase of as little as 1 mm in the outer surface of bone increases strength substantially. Adding bone to the endosteal surface also increases strength (Parfitt, 1994; Wang et al., 2009). Increases in testosterone may be a greater stimulus of periosteal expansion than estrogen since testosterone contributes to wider and stronger bones in males compared with females. Retrospective studies in tennis players and gymnasts suggest structural adaptations may persist many years later in adulthood and are greatest when “impact” activity is initiated in childhood (Kannus et al., 1995; Bass et al., 1998). RCTs on this issue are few, although the available data are promising (McKay et al., 2000; Fuchs et al., 2001; MacKelvie et al., 2001, 2003; Lindén et al., 2006). Thus, impact exercise begun in childhood may result in lasting structural changes that may contribute to increased bone strength and decreased fracture risk later in life (Turner and Robling, 2003; Ferrari et al., 2006).

Adipose tissue The adipose “organ” is composed of fat cells known as adipocytes (Ailhaud and Hauner, 1998). Adipocytes are distributed throughout the body in various organs and tissues, although they are largely clustered anatomically in structures called fat depots, which include a large number of adipocytes held together by a scaffold-like structure of collagen and other structural molecules. In the traditional view of the adipocyte, the cell provides a storage structure for fatty acids in the form of triacylglycerol molecules, with fatty acids being released when metabolic fuel is needed (Arner and Eckel, 1998). While adipocytes play this critical role, they are also involved in a number of endocrine, autocrine, and paracrine actions and play a key role in regulating other tissues and biological functions, for example, immunity and blood pressure, energy balance, glucose and lipid metabolism, and energy demands of exercise (Ailhaud and Hauner, 1998; Frühbeck et al., 2001). The role of adipocytes in regulation of energy balance and in carbohydrate and lipid metabolism and the potential effects of physical activity on adipocyte function are of particular interest here, given growing concerns related to pediatric and adult obesity (Ogden et al., 2012) and the associated risk of cardiometabolic disease (Weiss et al., 2004; Eisenmann, 2007a,b; Steele et al., 2008). Metabolic differences among various fat depots are now well known (Frühbeck et al., 2001), and there is significant interest in the distribution of adipose tissue, the changes that occur during childhood and adolescence, and their clinical significance.

Adipocytes increase in size (hypertrophy) and number (hyperplasia) from birth through childhood and adolescence and into young adulthood

to accommodate energy storage needs. The number of adipocytes has been estimated to increase from about 5 billion at birth to 30 billion to 50 billion in the nonobese adult, with an increase in average diameter from about 30-40 μm at birth to about 80-100 μm in the young adult (Knittle et al., 1979; Bonnet and Rocour-Brumioul, 1981; Chumlea et al., 1982). In total the adipose organ contains about 0.5 kg of adipocytes at birth in both males and females, increasing to approximately 10 kg in average-weight-for-height males and 14 kg in females (Malina et al., 2004). There is wide interindividual variation, however, and the difficulty of investigating changes in the number and size of adipocytes is obvious given the invasiveness of the required biopsy procedures; understandably, then, data on these topics are scarce in children and adolescents. Also, since only subcutaneous depots are accessible, results must be extrapolated from a few sites.

Based on such information, the average size of adipocytes has been reported to increase two- to threefold in the first year of life, with little increase in nonobese boys and girls until puberty (Malina et al., 2004). A small increase in average adipocyte size at puberty is more obvious in girls than in boys. There is considerable variation in size across various subcutaneous sites and between subcutaneous and internal depots. The number of adipocytes is difficult to estimate. Available data suggest that the cellularity of adipose tissue does not increase significantly in early postnatal life (Malina et al., 2004). Thus, gain in fat mass is the result of an increase in the size of existing adipocytes. From about 1-2 years of age and continuing through early and middle childhood, the number of adipocytes increases gradually two- to threefold. With puberty the number practically doubles, followed by a plateau in late adolescence and early adulthood. The number of adipocytes is similar in boys and girls until puberty, when girls experience a greater increase than boys.

The increases in the number of adipocytes during infancy and puberty are considered critical for enlargement of the adipose tissue organ and for the risk of obesity. Since size and number are linked, the number of adipocytes can potentially increase at any age if fat storage mechanisms are stimulated by chronic energy surfeit (Hager, 1981; Chumlea et al., 1982). Energy expenditure through regular physical activity is a critical element in preventing energy surfeit and excess adiposity. While cellularity undoubtedly is strongly genetically determined, regular physical activity, through its contribution to energy expenditure, can contribute to less adipocyte hyperplasia by limiting hypertrophy.

Fat distribution Fat distribution refers to the location of fat depots on the body. The metabolic activities of fat depots differ, and small variation can have a long-term impact on fat distribution. Differences in metabolic properties across depots also have clinical implications. Visceral adipose tissue

in the abdominal cavity is more metabolically active (reflected by free fatty acid flux) than adipose tissue in other areas (Arner and Eckel, 1998), and higher amounts of visceral adipose tissue are associated with greater risk of metabolic complications, such as type 2 diabetes and cardiovascular disease (Daniels et al., 1999; He et al., 2007; Dencker et al., 2012). In contrast, subcutaneous fat, particularly in the gluteofemoral region, is generally associated with a lower risk of cardiometabolic disease. Age- and sex-associated variations in fat distribution contribute to age- and sex-associated differences in cardiometabolic disease prevalence. Girls have more subcutaneous fat than boys at all ages, although relative fat distribution is similar. After a rapid rise in subcutaneous fat in the first few months of life, both sexes experience a reduction through age 6 or 7 (Malina and Roche, 1983; Malina and Bouchard, 1988; Malina, 1996). Girls then show a linear increase in subcutaneous fat, whereas boys show a small increase between ages 7 and 12 or 13 and then an overall reduction during puberty. The thickness of subcutaneous fat on the trunk is approximately one-half that of subcutaneous fat on the extremities in both boys and girls during childhood. The ratio increases with age in males during adolescence but changes only slightly in girls. In males the increasing ratio of trunk to extremity subcutaneous fat is a consequence of slowly increasing trunk subcutaneous fat and a decrease in subcutaneous fat on the extremities. In girls, trunk and extremity subcutaneous fat increase at a similar rate; thus the ratio is stable (Malina and Bouchard, 1988). As a consequence, the sex difference in the distribution of body fat develops during adolescence. It is important to note that changes in subcutaneous fat pattern do not necessarily represent changes in abdominal visceral adipose tissue.

Tracking of subcutaneous fat has been investigated based on skinfold thicknesses and radiographs of fat widths in males and females across a broad age range (Katzmarzyk et al., 1999; Campbell et al., 2012). Results indicate that subcutaneous fat is labile during early childhood. After age 7 to 8, correlations between subcutaneous fat in later childhood and adolescence and adult subcutaneous fat are significant and moderate. Longitudinal data on tracking of visceral adipose tissue are not available, but percent body fat does appear to track. Thus children and especially adolescents with higher levels of body fat have a higher risk of being overfat at subsequent examinations and in adulthood, although variation is considerable, with some individuals moving away from high fatness categories, while some lean children move into higher fatness categories.

In cross-sectional studies, active children and adolescents tend to have lower skinfold thicknesses and less overall body fat than their less active peers (Loftin et al., 1998; Rowlands et al., 2000; Stevens et al., 2004; Lohman et al., 2006), although the correlations are modest, reflecting variation in body composition at different levels of physical activity, as

well as the difficulty of measuring physical activity. Longitudinal studies indicate small differences in fatness between active and inactive boys and girls. Although some school-based studies of the effects of physical activity on body composition have reported changes in BMI or skinfolds in the desired direction (Gortmaker et al., 1999; McMurray et al., 2002), most have not shown significant effects. High levels of physical activity are most likely needed to modify skinfold thicknesses and percent body fat. In adults, visceral adipose tissue declines with weight loss with exercise. In contrast, in a study of obese children aged 7-11, a 4-month physical activity program resulted in minimal change in abdominal visceral adipose tissue but a significant loss in abdominal subcutaneous adipose tissue (Gutin and Owens, 1999). In adults, decreases in fatness with exercise are due to a reduction in fat cell size, not number (You et al., 2006); whether this is true in children is not certain but appears likely. Given that adipocyte hypertrophy may trigger adipocyte hyperplasia (Ballor et al., 1998), energy expenditure through regular physical activity may be important in preventing excess adipose tissue cellularity. Regular physical activity also affects adipose tissue metabolism so that trained individuals have an increased ability to mobilize and oxidize fat, which is associated with increased levels of lipolysis, an increased respiratory quotient, and a lower risk of obesity (Depres and Lamarche, 2000).

Cardiorespiratory System

The ability to perform sustained activity under predominantly aerobic conditions depends on the capacity of the cardiovascular and pulmonary systems to deliver oxygenated blood to tissues and on the ability of tissues (primarily skeletal muscle) to extract oxygen and oxidize substrate. By age 2 the systems are fully functional, although young children lack the cardiorespiratory capacity of older children and adults because of their small size (Malina et al., 2004). Children’s aerobic capacity and consequently their ability to exercise for longer periods of time increase as they grow. Maximal aerobic power (liters per minute) increases fairly linearly in boys until about age 16, whereas it increases in girls until about age 13 and then plateaus during adolescence (Malina et al., 2004; Eisenmann et al., 2011). Differences between boys and girls are small (~10 percent) during childhood and greater after the adolescent growth spurt, when girls have only about 70 percent of the mean value of boys. Changes with age and sex differences are explained largely by differences in the size of the relevant tissues. Dimensions of the heart and lungs enlarge with age in a manner consistent with the increase in body mass and stature (Malina et al., 2004). The increase in the size of the heart is associated with increases in stroke volume (blood pumped per beat) and cardiac output (product of stroke vol-

ume and heart rate, liters per minute), despite a decline in heart rate during growth. Similarly, increase in lung size (proportional to growth in height) results in greater lung volume and ventilation despite an age-associated decline in breathing frequency. From about age 6 to adulthood, maximal voluntary ventilation approximately doubles (50-100 L/min) (Malina et al., 2004). The general pattern of increase as a function of height is similar in boys and girls. In both, lung function tends to lag behind the increase in height during the adolescent growth spurt. As a result, peak gains in lung function occur about 2 years earlier in girls than in boys.

Blood volume is highly related to body mass and heart size in children and adolescents, and it is also well correlated with maximal oxygen uptake during childhood and adolescence (Malina et al., 2004). Blood volume increases from birth through adolescence, following the general pattern for changes in body mass. Both red blood cells and hemoglobin have a central role in transport of oxygen to tissues. Hematocrit, the percentage of blood volume explained by blood cells, increases progressively throughout childhood and adolescence in boys, but only through childhood in girls. Hemoglobin content, which is related to maximal oxygen uptake, heart volume, and body mass, increases progressively with age into late adolescence. Males have greater hemoglobin concentrations than females, especially relative to blood volume, which has functional implications for oxygen transport during intense exercise.

Growth in maximal aerobic power is influenced by growth in body size, so controlling for changes in body size during growth is essential. Although absolute (liters per minute) aerobic power increases into adolescence relative to body weight, there is a slight decline in both boys and girls, suggesting that body weight increases at a faster rate than maximal oxygen consumption, particularly during and after the adolescent growth spurt (Malina et al., 2004). Changes in maximal oxygen consumption during growth tend to be related more closely to fat-free mass than to body mass. Nevertheless, sex differences in maximal oxygen consumption per unit fat-free mass persist, and maximal oxygen consumption per unit fat-free mass declines with age.

Improvements in cardiorespiratory function—involving structural and functional adaptations in the lungs, heart, blood, and vascular system, as well as the oxidative capacity of skeletal muscle—occur with regular vigorous- and moderate-intensity physical activity (Malina et al., 2004). Concern about the application of invasive techniques limits the available data on adaptations in the oxygen transport system in children. Nevertheless, it is clear that aerobic capacity in youth increases with activity of sufficient intensity and that maximal stroke volume, blood volume, and oxidative enzymes improve after exercise training (Rowland, 1996). Training-induced changes in other components of the oxygen transport system remain to be determined.

Health- and Performance-Related Fitness

Physical fitness is a state of being that reflects a person’s ability to perform specific exercises or functions and is related to present and future health outcomes. Historically, efforts to assess the physical fitness of youth focused on measures designed to evaluate the ability to carry out certain physical tasks or activities, often related to athletic performance. In more recent years, the focus has shifted to greater emphasis on evaluating health-related fitness (IOM, 2012a) and assessing concurrent or future health status. Health- and performance-related fitness, while overlapping, are different constructs. Age- and sex-related changes in the components of both are strongly linked to the developmental changes in tissues and systems that occur during childhood and adolescence. Although genetic factors ultimately limit capacity, environmental and behavioral factors, including physical activity, interact with genes to determine the degree to which an individual’s full capacity is achieved.

Health-Related Fitness

Cardiorespiratory endurance, muscular strength and endurance, flexibility, and body composition are components of health-related fitness historically assessed in school-based fitness assessment programs (IOM, 2012a). These components of health-related fitness are considered important since they can be linked to the risk of cardiometabolic disease and musculoskeletal disability, chronic hypokinetic-related diseases.

Cardiorespiratory endurance Cardiorespiratory (aerobic) endurance reflects the functioning of the pulmonary and cardiovascular systems to deliver oxygen and the ability of tissues (primarily skeletal muscle) to extract oxygen from the blood. Defined clinically as the maximum oxygen consumption during a maximal graded exercise test, in practice it is usually measured indirectly as performance on a field test of endurance, such as 1- or 2-mile run time (IOM, 2012a). During childhood, aerobic capacity approximately doubles in both boys and girls, although girls on average possess a lower capacity. Males continue to improve during adolescence, up to ages 17-18, while aerobic capacity plateaus around age 14 in females (Malina et al., 2004), resulting in an approximately 20 percent difference between males and females (Rowland, 2005).

Favorable associations have been found between aerobic endurance and high-density lipoproteins, systolic blood pressure, diastolic blood pressure, BMI, measures of fatness, arterial stiffness, and measures of insulin sensitivity (Boreham et al., 2004; Imperatore et al., 2006; Hussey et al., 2007; Ondrak et al., 2007). Some evidence suggests a decline in aerobic endurance among U.S. youth in recent decades (Eisenmann, 2003; Carnethon et al.,

2005; Pate et al., 2006), coincident with increased sedentariness and obesity and a greater prevalence of metabolic syndrome in youth. Aerobic exercise has been shown to increase cardiorespiratory endurance by about 5-15 percent in youth (Malina et al., 2004; HHS, 2008). The programs that produce this benefit involve continuous vigorous- or moderate-intensity aerobic activity of various types for 30-45 minutes per session at least 3 days per week over a period of at least 1-3 months (Baquet et al., 2002); improvements are greater with more frequent exercise (Baquet et al., 2003).

Muscle strength and endurance Muscle strength is defined as the highest force generated during a single maximum voluntary contraction, whereas muscle endurance is the ability to perform repeated muscular contraction and force development over a period of time. Muscle strength and endurance are correlated, especially at higher levels of force production. Muscle strength is proportional to the cross-sectional area of skeletal muscle; consequently, strength growth curves parallel growth curves for body weight and skeletal muscle mass (Malina et al., 2004).

Both males and females show impressive increases in muscle strength from childhood to adolescence. Strength in children increases linearly, with boys having a slight advantage over girls. However, these sex differences are magnified during the adolescent years as a result of maturation (Malina and Roche, 1983). Differences in muscle strength between boys and girls become more apparent after puberty, primarily as a result of the production of sex steroid hormones. In boys the increase in strength during adolescence lags behind the growth spurt by at least a year (peak height velocity), which may explain why some boys experience a brief period of clumsiness or awkwardness during puberty, as they have not yet acquired the muscle strength necessary to handle the changes associated with their larger bodies. Muscle strength increases at its greatest rate approximately 1 year after peak height velocity in boys, whereas for girls the strength spurt generally occurs during the same year as peak height velocity (Bar-Or, 1983).

A compelling body of evidence indicates that with resistance training children and adolescents can significantly increase their strength above that expected as a result of normal growth and maturation, provided that the training program is of sufficient intensity, volume, and duration (Committee on Sports Medicine Fitness, 2001). Both boys and girls can benefit, and strength gains in children as young as 5-6 have been reported (Faigenbaum et al., 2009), although most studies are of older children and adolescents. Gains in muscle strength of about 30 percent are typical, although considerably larger gains have been reported. Adolescents make greater gains than preadolescents in absolute strength, whereas reported relative (percent above initial strength) gains in strength during preadolescence and adolescence are similar. A variety of programs and modalities have proved

efficacious (Council on Sports Medicine Fitness, 2008), as long as load (~10-15 repetitions maximum) and duration (~8-20 weeks) are adequate. As in adults, training adaptations in youth are specific to the muscle action or muscle groups that are trained, and gains are transient if training is not maintained (Faigenbaum et al., 2009).

Youth resistance training, as with most physical activities, does carry some degree of risk of musculoskeletal injury, yet the risk is no greater than that associated with other sports and activities in which children and adolescents participate (Council on Sports Medicine Fitness, 2008; Faigenbaum et al., 2009) as long as age-appropriate training guidelines are followed. A traditional area of concern has been the potential for training-induced damage to growth cartilage, which could result in growth disturbances. However, a recent review found no reports of injury to growth cartilage in any prospective study of resistance training in youth and no evidence to suggest that resistance training negatively impacts growth and maturation during childhood and adolescence (Faigenbaum et al., 2009). Injuries typically occur in unsupervised settings and when inappropriate loads and progressions are imposed.

In addition to the obvious goal of gaining strength, resistance training may be undertaken to improve sports performance and prevent injuries, rehabilitate injuries, and enhance health. Appropriately supervised programs emphasizing strengthening of trunk muscles in children theoretically benefit sport-specific skill acquisition and postural control, although these benefits are difficult to study and thus are supported by little empirical evidence (Council on Sports Medicine Fitness, 2008). Similarly, results are inconsistent regarding the translation of increased strength to enhanced athletic performance in youth. Limited evidence suggests that strength-training programs that address common overuse injuries may help reduce injuries in adolescents, but whether the same is true in preadolescents is unclear (Council on Sports Medicine Fitness, 2008). Increasing evidence suggests that strength training, like other forms of physical activity, has a beneficial effect on measurable health indices in youth, such as cardiovascular fitness, body composition, blood lipid profiles and insulin sensitivity (Faigenbaum, 2007; Benson et al., 2008), bone mineral density and bone geometry (Morris et al., 1997; MacKelvie et al., 2004), and mental health (Holloway et al., 1988; Faigenbaum et al., 1997; Annesi et al., 2005; Faigenbaum, 2007). Some work has shown that muscle fitness, reflected in a composite index combining measures of muscle strength and endurance, and cardiorespiratory fitness are independently and negatively associated with clustered metabolic risk (Steene-Johannessen et al., 2009). Moreover, children with low muscle strength may be at increased risk of fracture with exercise (Clark et al., 2011). Finally, muscle hypertrophy, which adds to fat-free mass, contributes to resting metabolic rate and therefore total daily

energy expenditure. Resistance training may be particularly useful for raising metabolic rate in overweight and obese children without the risk associated with higher-impact activities (Watts et al., 2005; Benson et al., 2007).

Flexibility Flexibility has been operationally defined as “the intrinsic property of body tissues, including muscle and connective tissues, that determines the range of motion achievable without injury at a joint or group of joints” (IOM, 2012b, p. 190). At all ages, girls demonstrate greater flexibility than boys, and the difference is greatest during the adolescent growth spurt and sexual maturation. Perhaps the most common field measure of flexibility in children and youth is the sit-and-reach test (IOM, 2012b) of low-back flexibility. Low-back flexibility as measured by this test is stable in girls from age 5 to 11 and increases until late adolescence. In boys, low-back flexibility declines linearly starting at age 5, reaching its nadir at about age 12, and then increases into late adolescence. The unique pattern of age- and sex-associated variation is related to the growth of the lower extremities and the trunk during adolescence. In boys the nadir in low-back flexibility coincides with the adolescent growth spurt in leg length. In both boys and girls, the increase during adolescence coincides with the growth spurt in trunk length and arm length, which influences reach. Flexibility in both males and females tends to decline after age 17, in part as a result of a decline in physical activity and normal aging.

The principal health outcomes hypothesized to be associated with flexibility are prevention of and relief from low-back pain, prevention of musculoskeletal injury, and improved posture. These associations have been studied in adults, with equivocal results (Plowman, 1992). Although flexibility has long been included in national youth fitness tests, it has proven difficult to establish a link between flexibility and health (IOM, 2012a). In contrast to other fitness components that are general or systemic in nature, flexibility is highly specific to each joint of the body. Although appropriate stretching may increase flexibility, establishing a link to improved functional capacity and fitness is difficult. A few studies suggest that improvements in flexibility as measured by the sit-and-reach test may be related to less low-back pain (Jones et al., 2007; Ahlqwist et al., 2008), but the evidence is weak. Consequently, the Institute of Medicine (IOM) Committee on Fitness Measures and Health Outcomes in its recent report elected to forego recommending a flexibility test for a national youth fitness test battery pending further research to confirm the relationship between flexibility and health and to develop national normative data (IOM, 2012a).

Body composition Body composition is the component of health-related fitness that relates to the relative amount of adipose tissue, muscle, bone, and other vital components (e.g., organs, connective tissues, fluid compart-

ments) that make up body weight. Most feasible methods for assessing body composition are based on models that divide the body into fat and fat-free (all nonfat constituents) components (Going et al., 2012). Although fat mass and adipose tissue are not equivalent components, fat mass is easier to estimate than adipose tissue, and it is correlated with performance and disease risk. In settings in which estimation of body fat is difficult, weight-for-height ratios often are used as surrogates for body composition. Indeed, definitions of pediatric overweight and obesity have been based on BMI, calculated as weight in kilograms divided by height squared. Child and adolescent obesity defined by BMI remains at all-time highs. Population surveys indicate that approximately 33 percent of all boys and girls are overweight, and nearly one in five are obese (Ogden and Flegal, 2011). The tendency for excess fatness to persist from childhood and adolescence into adulthood (Daniels et al., 2005), coupled with the strong association between obesity and chronic disease (Weiss and Caprio, 2005; Barlow, 2007), has caused great concern for future obesity levels and the health of youth and adults alike (IOM, 2005, 2012b).

The increase in prevalence of obesity is undoubtedly due to a mismatch between energy intake and expenditure. Population surveys have shown that few children and youth meet recommended levels of daily physical activity (see Chapter 2 ). Prospective studies have shown a significant and inverse relationship between habitual physical activity and weight gain (Berkey et al., 2003), and in some studies physical activity is a better predictor of weight gain than estimates of calorie or fat intake (Berkey et al., 2000; Janssen et al., 2005). These relationships are better established in adults than in children and youth, although even in preschool children, low levels of physical activity, estimated from doubly labeled water, were found to be indicative of higher body fat content (Davies et al., 1995). While studies of exercise without caloric restriction generally show only small effects on body weight, significant albeit moderate reductions of body fat are generally reported (Eisenmann, 2003). Moreover, even in the absence of significant weight loss, exercise has beneficial effects on risk factors for cardiometabolic disease (Ross and Bradshaw, 2009; Gutin and Owens, 2011).

Body mass index Changes in weight for height with growth and maturation for U.S. boys and girls are described in CDC growth curves (Kuczmarski et al., 2000). Current growth curves were derived from U.S. population surveys conducted before the increase in weight for height that defines today’s pediatric obesity epidemic. In boys and girls, BMI declines during early childhood, reaching its nadir at about ages 5-6, and then increases through adolescence. A gender difference emerges during puberty, with males gaining greater fat-free mass than females. Both the

period of “adiposity rebound” (the increase in BMI in midchildhood following the decline in early childhood) and puberty are times of risk for excess fat gain that correlates with future adiposity (Rolland-Cachera et al., 1984). Physical activity and BMI are inversely correlated in children and adolescents, although the correlations are modest (Lohman et al., 2006), reflecting the difficulty of measuring physical activity, as well as variation in body composition and physical activity at a given weight (Rowlands et al., 2000). Indeed, when studied separately, fat mass index (FMI, or fat mass divided by height squared) and fat-free mass index (FFMI, or fat-free mass divided by height squared) are both inversely related to physical activity. With FMI controlled, however, FFMI is positively related to physical activity, indicating that, for a given level of body fat, individuals with more fat-free mass are more active (Lohman et al., 2006). BMI cut-points for defining overweight and obesity have historically been based on age- and gender-specific population distributions of BMI. Recent work has shown good correspondence between BMI standards and percent fat standards that are referenced to health criteria (Laurson et al., 2011). These new standards should prove useful for identifying children and adolescents at risk for higher levels of cardiometabolic risk factors.

Percent body fat Direct measures of body fat as a percent of weight provide a better index of adiposity and health risk than BMI (Zeng et al., 2012), which is confounded by variation in lean tissue mass relative to height. Recently, percent fat growth curves were established for representative samples of U.S. boys and girls using National Health and Nutrition Examination Survey (NHANES) data (Laurson et al., 2011; Ogden and Flegal, 2011). Median percent fat for boys aged 5-18 ranged from 14 to 19 percent and for girls across the same ages 15 to 28 percent. In both boys and girls, percent fat increases slowly during early childhood, with girls having a consistently greater relative fatness than boys after ages 5-6. In girls, percent fat increases gradually throughout adolescence in the same manner as fat mass. In boys, percent fat increases gradually until the adolescent growth spurt and thereafter gradually declines until about age 16-17, reflecting the rapid growth in fat-free mass relative to fat mass. After age 17, percent fat in males gradually increases again into adulthood.

The increased prevalence of child and adolescent obesity as defined by BMI presumably also reflects increased adiposity, although the degree is not certain as population-based estimates of percent fat have only recently been developed (Laurson et al., 2011). Health-related percent fat standards recently were developed by determining levels of body fat associated with greater occurrence of chronic disease risk factors defined by metabolic syndrome (Going et al., 2011). In boys and girls aged 12-18, body fat above

20-24 percent and above 27-31 percent, respectively, was predictive of metabolic syndrome.

Physical activity is inversely correlated with percent body fat (Rowlands et al., 2000; Lohman et al., 2006), although the correlations are modest, and changes in overall fatness as well as subcutaneous adipose tissue with habitual physical activity are reasonably well documented in children and adolescents (Gutin and Humphries, 1998; Gutin and Owens, 1999; Dionne et al., 2000). In youth, as in adults, the effects of exercise without caloric restriction are modest and are influenced by the initial level of body fat and the duration and regimen of exercise (Going, 1999). Experimental studies have documented reductions in percent body fat with aerobic exercise, especially in children and adolescents who are overweight or obese at the initiation of an exercise program (Davis et al., 2012). Regular physical activity also affects adipose tissue metabolism (Gutin and Owens, 1999). Individuals who engage in aerobic endurance exercise training have an increased ability to mobilize and oxidize fat, which is associated with increased levels of lipolysis (Depres and Lamarche, 2000). Similar information on adipose tissue metabolism in children and youth is lacking, although one can reasonably expect similar adaptations in older adolescents.

Metabolic syndrome The tendency for risk factors for cardiometabolic disease to cluster, now called metabolic syndrome, is well recognized in adults (Alberti and Zimmet, 1998). Similar clustering occurs in older children and especially adolescents (Cook et al., 2003), and interest in metabolic syndrome has increased, driven by the increased prevalence of pediatric obesity and the increasing incidence and earlier onset of type 2 diabetes in youth. There is as yet no accepted definition of metabolic syndrome for use in pediatric populations (Jolliffe and Janssen, 2007). Typically, adult definitions are extrapolated to children and adolescents, with appropriate adjustments of the thresholds for the defining variables. Perhaps the most common approach is to emulate the National Cholesterol Education Program (NCEP), which defines metabolic syndrome as exceeding thresholds on three of five components: waist circumference, blood pressure (systolic or diastolic), blood lipids (high-density lipoprotein [HDL] and triglycerides), and blood glucose levels (NIH, 2001).

The concept of metabolic syndrome is useful as it provides an integrated index of risk, and it recently was used to derive health-related percent-body-fat standards (Laurson et al., 2011). Based on NHANES data, the prevalence of metabolic syndrome varies with the degree of obesity, and it is estimated at 4-6 percent of children and adolescents (Cook et al., 2003; Dubose et al., 2007); among obese youth it may be as high as 30-50 percent (Weiss et al., 2004). Youth with metabolic syndrome have an increased risk of type 2 diabetes and cardiovascular disease. In adults a

loss of 5-10 percent of body weight through calorie restriction and exercise has been shown to reduce the risk of cardiometabolic disease by improving risk factors (Diabetes Prevention Program Research Group, 2002; Ross and Janiszewski, 2008). In particular, weight loss results in reduced visceral adipose tissue, a strong correlate of risk (Knowler et al., 2002), as well as lower blood pressure and blood glucose levels due to improved insulin sensitivity. Even without significant weight loss, exercise can have significant effects in adults by improving glucose metabolism, improving lipid and lipoprotein profiles, and lowering blood pressure, particularly for those who are significantly overweight (Ross and Bradshaw, 2009). Similar benefits have been observed in adolescents.

A growing body of literature addresses the associations of physical activity, physical fitness, and body fatness with the risk of metabolic syndrome and its components in children and especially adolescents (Platat et al., 2006; McMurray et al., 2008; Rubin et al., 2008; Thomas and Williams, 2008; Christodoulos et al., 2012). Studies in adults have shown that higher levels of physical activity predict slower progression toward metabolic syndrome in apparently healthy men and women (Laaksonen et al., 2002; Ekelund et al., 2005), an association that is independent of changes in body fatness and cardiorespiratory fitness (Ekelund et al., 2007). Few population studies have focused on these relationships in children and adolescents, and the use of self-reported activity, which is imprecise in these populations, tends to obscure associations. In a large sample of U.S. adolescents aged 12-19 in the 1999-2002 NHANES, for example, there was a trend for metabolic syndrome to be more common in adolescents with low activity levels than in those with moderate or high activity levels, although the differences among groups were not statistically significant (Pan and Pratt, 2008). Moreover, for each component of metabolic syndrome, prevalence was generally lower with higher physical activity levels, and adolescents with low physical activity levels had the highest rates of all metabolic syndrome components.

The association between cardiorespiratory fitness and metabolic syndrome also was examined in the 1999-2002 NHANES (Lobelo et al., 2010). Cardiorespiratory fitness was measured as estimated peak oxygen consumption using a submaximal treadmill exercise protocol, and metabolic syndrome was represented as a “clustered score” derived from five established risk factors for cardiovascular disease, an adiposity index, insulin resistance, systolic blood pressure, triglycerides, and the ratio of total to HDL cholesterol. Mean clustered risk score decreased across increasing fifths (quintiles) of cardiorespiratory fitness in both males and females. The most significant decline in risk score was observed from the first (lowest) to the second quintile (53.6 percent and 37.5 percent in males and females, respectively), and the association remained significant in both overweight

and normal-weight males and in normal-weight females. Other studies, using the approach of cross-tabulating subjects into distinct fitness and fatness categories, have examined associations of fitness and fatness with metabolic syndrome risk (Eisenmann et al., 2005, 2007a,b; Dubose et al., 2007). Although different measures of fitness, fatness, and metabolic syndrome risk were used, the results taken together across a wide age range (7-18) show that fitness modifies the influence of fatness on metabolic syndrome risk. In both males and females, high-fit/low-fatness subjects have less metabolic syndrome risk than low-fit/high-fatness subjects (Eisenmann, 2007).

That many adult chronic health conditions have their origins in childhood and adolescence is well supported (Kannel and Dawber, 1972; Lauer et al., 1975; Berenson et al., 1998; IOM, 2004). Both biological (e.g., adiposity, lipids) and behavioral (e.g., physical activity) risk factors tend to track from childhood and especially adolescence into adulthood. Childhood BMI is related to adult BMI and adiposity (Guo et al., 1994, 2000; Freedman et al., 2005), and as many as 80 percent of obese adolescents become obese adults (Daniels et al., 2005). Coexistence of cardiometabolic risk factors, even at young ages (Dubose et al., 2007; Ramírez-Vélez et al., 2012), has been noted, and these components of metabolic syndrome also have been shown to track to adulthood (Bao et al., 1994; Katzmarzyk et al., 2001; Huang et al., 2008). Landmark studies from the Bogalusa Heart Study (Berenson et al., 1998; Li et al., 2003) and others (Mahoney et al., 1996; Davis et al., 2001; Morrison et al., 2007, 2008) have demonstrated that cardiometabolic risk factors present in childhood are predictive of adult disease.

The benefits of exercise for prevention and treatment of cardiometabolic disease in adults are well described (Ross et al., 2000; Duncan et al., 2003; Gan et al., 2003; Irwin et al., 2003; Lee et al., 2005; Sigal et al., 2007; Ross et al., 2012). Prospective studies examining the effects of exercise on metabolic syndrome in children and adolescents remain limited, and it is important to refrain from extrapolating intervention effects observed in adults to youth, although one might reasonably assume the benefits in older adolescents to be similar to those in young adults. Indeed, based on the inverse associations of physical activity and physical fitness with metabolic syndrome (Kim and Lee, 2009) and on the available intervention studies, some experts have recommended physical activity as the main therapeutic tool for prevention and treatment of metabolic syndrome in childhood (Brambilla et al., 2010). Comparative studies in adults have shown that the effect of exercise on weight is limited and generally less than that of calorie restriction (Brambilla et al., 2010). Moreover, the relative effectiveness of diet and exercise depends on the degree of excess fatness (Brambilla et al., 2010). Comparative studies in children and youth are few, as behavioral

interventions in overweight children and adolescents commonly combine exercise and dietary restriction, making it difficult to disentangle their independent effects. Nonetheless, diet and exercise have different effects on body composition: While both contribute to fat loss, only exercise increases muscle mass and thus has a direct effect on metabolic health. In children and youth, as in adults, the effect of exercise on cardiometabolic risk factors is greater in overweight/obese youth than in their normal-weight peers (Kang et al., 2002; Lazaar et al., 2007).

Exercise also may have important benefits even without significant modification of body composition (Bell et al., 2007). Experimental studies in overweight and obese youth have shown that exercise leads to reductions in visceral fat (Owens et al., 1999; Gutin et al., 2002; Lee at al., 2005; Barbeau et al., 2007; Kim and Lee, 2009) without a significant change in BMI, as well as improvement in markers of metabolic syndrome, primarily fasting insulin and insulin resistance (Treuth et al., 1998; Ferguson et al., 1999; Carrel et al., 2005; Nassis et al., 2005; Meyer et al., 2006; Shaibi et al., 2006; Bell et al., 2007). Results from experimental studies of the effects of exercise on lipids and lipoproteins (Stoedefalke et al., 2000; Kelley and Kelley, 2008; Janssen and LeBlanc, 2010) are mixed. Although some studies have shown improved lipid and lipoprotein profiles, primarily a decrease in low-density lipoprotein (LDL) cholesterol and triglyceride concentrations and an increase in HDL cholesterol (Ferguson et al., 1999), other studies have shown no improvement in these outcomes (Kelley and Kelley, 2008). In part, such conflicting results are likely due to initial differences in body composition and severity of hyperlipidemia. Well-controlled exercise training studies in obese children (Escalante et al., 2012) and children with adverse blood lipid and lipoprotein profiles have shown positive alterations in their profiles (Stoedefalke et al., 2000), whereas results in normolipid-emic children and adolescents are equivocal. Similarly, exercise has little effect on resting blood pressure in normotensive children and adolescents (Kelley and Kelley, 2008), whereas reductions in resting systolic and sometimes diastolic pressures have been reported in youth with high blood pressure (Hagberg et al., 1983, 1984; Danforth et al., 1990; Ewart et al., 1998; Farpour-Lambert et al., 2009; Janssen and LeBlanc, 2010).

In adults, physical activity is inversely associated with low-grade inflammation (Wärnberg et al., 2010; Ertek and Cicero, 2012), which is now recognized as a significant feature of metabolic syndrome and an independent predictor of cardiometabolic disease (Malina, 2002). In obese children and adolescents, as in their adult counterparts, elevation of inflammatory markers is evident, and observational studies have shown significant relationships among physical activity, physical fitness, and inflammation (Isasi et al., 2003; Platat et al., 2006; Ruiz et al., 2007; Wärnberg et al., 2007; Wärnberg and Marcos, 2008). These relationships are better studied and

stronger in adolescents than in children. In one study of boys and girls aged 10-15, those who were obese and unfit had the highest levels of systemic inflammation, whereas those who were obese yet fit had levels as low as those who were lean and fit (Halle et al., 2004). In another study, low-grade inflammation was negatively associated with muscle strength in overweight adolescents after controlling for cardiorespiratory fitness, suggesting that high levels of muscle strength may counteract some of the negative consequences of higher levels of body fat (Ruiz et al., 2008). Experimental studies of the effects of exercise and markers of low-grade inflammation in children and adolescents are lacking. Improved cardiorespiratory fitness in adults (Church et al., 2002), however, has been shown to be inversely related to concentration of C-reactive protein (CRP), a marker of low-grade inflammation. In a small study of a lifestyle intervention entailing 45 minutes of physical activity 3 times per week for 3 months, a small reduction in body fat and an overall decrease in inflammatory factors (CRP, interleukin [IL]-6) were seen in obese adolescents (Balagopal et al., 2005).

Performance-Related Fitness

Speed, muscle power, agility, and balance (static and dynamic) are aspects of performance-related fitness that change during body development in predictable ways associated with the development of tissues and systems discussed above (Malina et al., 2004). Running speed and muscle power are related, and both depend on full development of the neuromuscular system. Running speed and muscle power are similar for boys and girls during childhood (Haubenstricker and Seefeldt, 1986). After puberty, largely because of differences in muscle mass and muscle strength, males continue to make significant annual gains, while females tend to plateau during the adolescent years. Sociocultural factors and increasing inactivity among girls relative to boys, along with changes in body proportion and a lowering of the center of gravity, may also contribute to gender differences (Malina et al., 2004).

Balance—the ability to maintain equilibrium—generally improves from ages 3 to 18 (Williams, 1983). Research suggests that females outperform males on tests of static and dynamic balance during childhood and that this advantage persists through puberty (Malina et al., 2004).

Motor performance is related in part to muscle strength. Increases in muscle strength as a result of resistance exercise were described above. A question of interest is whether gains in strength transfer to other performance tasks. Available results are variable, giving some indication that gains in strength are associated with improvement in some performance tasks, such as sprinting and vertical jump, although the improvements are generally small, highlighting the difficulty of distinguishing the effects

of training from changes expected with normal growth. Changes in body size, physique, and body composition associated with growth and maturation are important factors that affect strength and motor performance. The relationships vary among performance measures and with age, and these factors often are inadequately controlled in studies of components of performance-related fitness and performance tasks.

PSYCHOSOCIAL HEALTH

Research supports the positive impact of physical activity on the overall psychological health and social engagement of every student. A well-designed physical education curriculum provides students with social and emotional benefits (NASPE, 2001). Simultaneously, exposure to failure experiences, emphasis on competitive sports, and elitism for naturally inclined athletes, along with bullying and teasing of unfit, uncoordinated, and overweight youth, may be important factors discouraging participation in current and future physical activity (Kohl and Hobbs, 1998; Sallis et al., 2000; Allender et al., 2006). School-based physical activity, including physical education and sports, is designed to increase physical activity while also improving motor skills and development, self-efficacy, and general feelings of competency and engaging children socially (Bailey, 2006). The hoped-for psychosocial outcomes of physical education and other physical activity programs in the school setting have been found to be critical for continued physical activity across the life span and are themselves powerful long-term determinants of physical activity (Bauman et al., 2012). Unfortunately, significant gaps exist between the intent and reality of school-based physical education and other activity programs (HHS, 2013).

A large number of psychological and social outcomes have been examined. Specific aspects of psychosocial health showing a beneficial relationship to physical activity include, among others, self-efficacy, self-concept, self-worth (Haugen et al., 2011), social behaviors (Cradock et al., 2009), pro-school attitudes, motivation and goal orientation (Digelidis et al., 2003), relatedness, friendships (de la Haye et al., 2011; Macdonald-Wallis et al., 2011), task orientation, team building, bullying, and racial prejudice (Byrd and Ross, 1991). Most studies are descriptive, finding bidirectional associations between psychosocial outcomes and physical activity. Reviews and meta-analyses confirm a positive association between physical activity and self-esteem, especially for aerobic activities (McAuley, 1994).

Among psychosocial factors, self-efficacy (confidence in one’s ability to be physically active in specific situations) has emerged as an important correlate of physical activity from a large body of work based on the durable and practically useful social learning theory (Bandura and McClelland, 1977; Bandura, 1995). Bandura’s theory compels consideration of the

psychosocial and physical environments, the individual, and in this case the behavior of physical activity. Using this framework, physical activity itself has been shown to be a consistent positive correlate as well as a determinant of physical activity in children and adolescents. A large amount of reviewed research has found that physical education and physical activity experiences can increase children’s confidence in being active and lead to continued participation in physical activity (Bauman et al., 2012). RCTs have shown that both self-efficacy and social interactions leading to perceived social support influence changes in physical activity (Dishman et al., 2009). Skill mastery, confidence building, and group support are well-known strategies for advancing student learning and well-being in many educational domains in the school setting and apply equally to school physical education and other physical activity. Early observational studies of physical, social, and environmental determinants of physical activity at home, school, and recess indicated that prompts to be active (or not) from peers and adults accounted for a significant amount of the variance in directly observed physical activity (Elder et al., 1998). One longitudinal study following the variability and tracking of physical activity in young children showed that most of the variability in both home and recess activity was accounted for by short-term social and physical environmental factors, such as prompts from others and being outdoors (Sallis et al., 1995). Another study, examining activity among preschool children, found that, contrary to common belief, most of the time spent in preschool was sedentary, and correlates of activity were different for preschool boys and girls (Byun et al., 2011). In addition, significant variation in activity by preschool site was noted, indicating that local environmental conditions, including physical environment and equipment, policies, and teacher and administrative quality characteristics, play an important role in promoting physical activity (Brown et al., 2009).

Studies in middle and high school populations have strengthened the evidence base on relationships among self-efficacy, physical activity, and social support (from adults and peers). This research has highlighted the central contribution of self-efficacy and social support in protecting against a decline in activity levels among adolescent girls (Dishman et al., 2009, 2010). Evidence indicates further that these impacts spread to activities outside the school setting (Lytle et al., 2009). Findings of a related study suggest that leisure-time physical activity among middle school students was linked to motivation-related experiences in physical education (Cox et al., 2008).

A recent review of reviews (Bauman et al., 2012) found that population levels of physical activity are low and that consistent individual-level correlates of physical activity are age, sex, health status, self-efficacy, and previous physical activity. Physical activity declines dramatically as children progress from elementary through high school (Nader et al., 2008). Boys are con-

sistently found to be more active than girls from ages 4 to 9. For other age groups of children and adolescents, sex is correlated with but not a determinant of activity (Bauman et al., 2012). These findings suggest the need to tailor physical education and physical activity programs for youth specifically to increase self-efficacy and enjoyment of physical activity among girls (Dishman et al., 2005; Barr-Anderson et al., 2008; Butt et al., 2011).

In summary, a broad range of beneficial psychosocial health outcomes have been associated with physical activity. The promotion of more physical activity and quality physical education in the school setting is likely to result in psychosocially healthier children who are more likely to engage in physical activity as adults. Schools can play an important role in ensuring opportunities for physical activity for a segment of the youth population that otherwise may not have the resources to engage in such activity. It makes sense to assume that, if physical activity experiences and environments were once again structured into the daily school environment of children and adolescents, individuals’ feelings of self-efficacy regarding physical activity would increase in the U.S. population.

MENTAL HEALTH

Mental illness is a serious public health issue. It has been estimated that by 2010 mental illness will account for 15 percent of the global burden of disease (Biddle and Mutrie, 2008; Biddle and Asare, 2011). Young people are disproportionately affected by depression, anxiety, and other mental health disorders (Viner and Booy, 2005; Biddle and Asare, 2011). Approximately 20 percent of school-age children have a diagnosable mental health disorder (U.S. Public Health Service, 2000), and overweight children are at particular risk (Ahn and Fedewa, 2011). Mental health naturally affects academic performance on many levels (Charvat, 2012). Students suffering from depression, anxiety, mood disorders, and emotional disturbances perform more poorly in school, exhibit more behavioral and disciplinary problems, and have poorer attendance relative to mentally healthy children. Thus it is in schools’ interest to take measures to support mental health among the student population. In addition to other benefits, providing adequate amounts of physical activity in a way that is inviting and safe for children of all ability levels is one simple way in which schools can contribute to students’ mental health.

Impact of Physical Activity on Mental Health

Several recent reviews have concluded that physical activity has a positive effect on mental health and emotional well-being for both adults and children (Peluso and Guerra de Andrade, 2005; Penedo and Dahn, 2005;

Strong et al., 2005; Hallal et al., 2006; Ahn and Fedewa, 2011; Biddle and Asare, 2011). Numerous observational studies have established the association between physical activity and mental health but are inadequate to clarify the direction of that association (Strong et al., 2005). It may be that physical activity improves mental health, or it may be that people are more physically active when they are mentally healthy. Most likely the relationship is bidirectional.

Several longitudinal and intervention studies have clarified that physical activity positively impacts mental health (Penedo and Dahn, 2005; Strong et al., 2005). Physical activity has most often been shown to reduce symptoms of depression and anxiety and improve mood (Penedo and Dahn, 2005; Dishman et al., 2006; Biddle and Asare, 2011). In addition to reducing symptoms of depression and anxiety, studies indicate that regular physical activity may help prevent the onset of these conditions (Penedo and Dahn, 2005). Reductions in depression and anxiety are the commonly measured outcomes (Strong et al., 2005; Ahn and Fedewa, 2011). However, reductions in states of confusion, anger, tension, stress, anxiety sensitivity (a precursor to panic attacks and panic disorders), posttraumatic stress disorder/psychological distress, emotional disturbance, and negative affect have been observed, as well as increases in positive expectations; fewer emotional barriers; general well-being; satisfaction with personal appearance; and improved life satisfaction, self-worth, and quality of life (Heller et al., 2004; Peluso and Guerra de Andrade, 2005; Penedo and Dahn, 2005; Dishman et al., 2006; Hallal et al., 2006; Ahn and Fedewa, 2011; Biddle and Asare, 2011). Among adolescents and young adult females, exercise has been found to be more effective than cognitive-behavioral therapy in reducing the pursuit of thinness and the frequency of bingeing, purging, and laxative abuse (Sundgot-Borgen et al., 2002; Hallal et al., 2006). The favorable effects of physical activity on sleep may also contribute to mental health (Dishman et al., 2006).

The impact of physical activity on these measures of mental health is moderate, with effect sizes generally ranging from 0.4 to 0.7 (Biddle and Asare, 2011). In one meta-analysis of intervention trials, the RCTs had an effect size of 0.3, whereas other trials had an effect size of 0.57.

Ideal Type, Length, and Duration of Physical Activity

Intervention trials that examine the relationship between physical activity and mental health often fail to specify the exact nature of the intervention, making it difficult to determine the ideal frequency, intensity, duration, and type of physical activity involved (Penedo and Dahn, 2005; Ahn and Fedewa, 2011; Biddle and Asare, 2011).

Many different types of physical activity—including aerobic activity, resistance training, yoga, dance, flexibility training, walking programs, and body building—have been shown to improve mood and other mental health indicators. The evidence is strongest for aerobic physical activity, particularly for reduction of anxiety symptoms and stress (Peluso and Guerra de Andrade, 2005; Dishman et al., 2006; Martikainen et al., 2013), because more of these studies have been conducted (Peluso and Guerra de Andrade, 2005). One meta-analysis of RCTs concluded that physical activity interventions focused exclusively on circuit training had the greatest effect on mental health indicators, followed closely by interventions that included various types of physical activity (Ahn and Fedewa, 2011). Among studies other than RCTs, only participation in sports had a significant impact on mental health (Ahn and Fedewa, 2011). The few studies that investigated the impact of vigorous- versus lower-intensity physical activity (Larun et al., 2006; Biddle and Asare, 2011) found no difference, suggesting that perhaps all levels of physical activity may be helpful. Among adults, studies have consistently shown beneficial effects of both aerobic exercise and resistance training. Ahn and Fedewa (2011) concluded that both moderate and intense physical activity have a significant impact on mental health, although when just RCTs were considered, only intense physical activity was significant (Ahn and Fedewa, 2011). While physical activity carries few risks for mental health, it is important to note that excessive physical activity or specialization too early in certain types of competitive physical activity has been associated with negative mental health outcomes and therefore should be avoided (Peluso and Guerra de Andrade, 2005; Hallal et al., 2006). Furthermore, to reach all children, including those that may be at highest risk for inactivity, obesity, and mental health problems, physical activity programming needs to be nonthreatening and geared toward creating a positive experience for children of all skill and fitness levels (Amis et al., 2012).

Various types of physical activity programming have been shown to have a positive influence on mental health outcomes. Higher levels of attendance and participation in physical education are inversely associated with feelings of sadness and risk of considering suicide (Brosnahan et al., 2004). Classroom physical activity is associated with reduced use of medication for attention deficit hyperactivity disorder (Katz et al., 2010). And participation in recess is associated with better student classroom behavior, better focus, and less fidgeting (Pellegrini et al., 1995; Jarrett et al., 1998; Barros et al., 2009).

Strong evidence supports the short-term benefits of physical activity for mental health. Acute effects can be observed after just one episode and can last from a few hours to up to 1 day after. Body building may have a similar effect, which begins a few hours after the end of the exercise. The ideal

length and duration of physical activity for improving mental health remain unclear, however. Regular exercise is associated with improved mood, but results are inconsistent for the association between mood and medium- or long-term exercise (Dua and Hargreaves, 1992; Slaven and Lee, 1997; Dimeo et al., 2001; Dunn et al., 2001; Kritz-Silverstein et al., 2001; Sexton et al., 2001; Leppamaki et al., 2002; Peluso and Guerra de Andrade, 2005). Studies often do not specify the frequency and duration of physical activity episodes; among those that do, interventions ranged from 6 weeks to 2 years in duration. In their meta-analysis, Ahn and Fedewa (2011) found that, comparing interventions entailing a total of more than 33 hours, 20-33 hours, and less than 20 hours, the longer programs were more effective. Overall, the lack of reporting and the variable length and duration of reported interventions make it difficult to draw conclusions regarding dose (Ahn and Fedewa, 2011).

In addition to more structured opportunities, naturally occurring physical activity outside of school time is associated with fewer depressive symptoms among adolescents (Penedo and Dahn, 2005). RCTs have demonstrated that physical activity involving entire classrooms of students is effective in alleviating negative mental health outcomes (Ahn and Fedewa, 2011). Non-RCT studies have shown individualized approaches to be most effective and small-group approaches to be effective to a more limited extent (Ahn and Fedewa, 2011). Interventions have been shown to be effective in improving mental health when delivered by classroom teachers, physical education specialists, or researchers but may be most effective when conducted with a physical education specialist (Ahn and Fedewa, 2011). Many physical activity interventions include elements of social interaction and support; however, studies to date have been unable to distinguish whether the physical activity itself or these other factors account for the observed effects on mental health (Hasselstrom et al., 2002; Hallal et al., 2006). Finally, a few trials (Larun et al., 2006; Biddle and Asare, 2011) have compared the effects of physical activity and psychosocial interventions, finding that physical activity may be equally effective but may not provide any added benefit.

Subgroup Effects

Although studies frequently fail to report the age of participants, data on the effects of physical activity on mental health are strongest for adults participating in high-intensity physical activity (Ahn and Fedewa, 2011). However, evidence relating physical activity to various measures of mental health has shown consistent, significant effects on individuals aged 11-20. A large prospective study found that physical activity was inversely associated with depression in early adolescence (Hasselstrom et al., 2002; Hallal

et al., 2006); fewer studies have been conducted among younger children. Correlation studies have shown that the association of physical activity with depression is not affected by age (Ahn and Fedewa, 2011).

Few studies have examined the influence of other sociodemographic characteristics of participants on the relationship between physical activity and mental health (Ahn and Fedewa, 2011), but studies have been conducted in populations with diverse characteristics. One study of low-income Hispanic children randomized to an aerobic intensity program found that the intervention group was less likely to present with depression but did not report reduced anxiety (Crews et al., 2004; Hallal et al., 2006). A study that included black and white children (aged 7-11) found that a 40-minute daily dose of aerobic exercise significantly reduced depressive symptoms and increased physical appearance self-worth in both black and white children and increased global self-worth in white children compared with controls (Petty et al., 2009). Physical activity also has been positively associated with mental health regardless of weight status (normal versus overweight) or gender (male versus female) (Petty et al., 2009; Ahn and Fedewa, 2011); however, results are stronger for males (Ahn and Fedewa, 2011).

Improvements in mental health as a result of physical activity may be more pronounced among clinically diagnosed populations, especially those with cognitive impairment or posttraumatic stress disorder (Craft and Landers, 1998; Ahn and Fedewa, 2011; Biddle and Asare, 2011). Evidence is less clear for youth with clinical depression (Craft and Landers, 1998; Larun et al., 2006; Biddle and Asare, 2011). Individuals diagnosed with major depression undergoing an intervention entailing aerobic exercise have shown significant improvement in depression and lower relapse rates, comparable to results seen in participants receiving psychotropic treatment (Babyak et al., 2000; Penedo and Dahn, 2005). One program for adults with Down syndrome providing three sessions of exercise and health education per week for 12 weeks resulted in more positive expectations, fewer emotional barriers, and improved life satisfaction (Heller et al., 2004; Penedo and Dahn, 2005). Ahn and Fedewa (2011) found that, compared with nondiagnosed individuals, physical activity had a fivefold greater impact on those diagnosed with cognitive impairment and a twofold greater effect on those diagnosed with emotional disturbance, suggesting that physical activity has the potential to improve the mental health of those most in need.

In sum, although more studies are needed, and there may be some differences in the magnitude and nature of the mental health benefits derived, it appears that physical activity is effective in improving mental health regardless of age, ethnicity, gender, or mental health status.

Sedentary Behavior

Sedentary behavior also influences mental health. Screen viewing in particular and sitting in general are consistently associated with poorer mental health (Biddle and Asare, 2011). Children who watch more television have higher rates of anxiety, depression, and posttraumatic stress and are at higher risk for sleep disturbances and attention problems (Kappos, 2007). Given the cross-sectional nature of these studies, however, the direction of these associations cannot be determined. A single longitudinal study found that television viewing, but not playing computer games, increased the odds of depression after 7-year follow-up (Primack et al., 2009; Biddle and Asare, 2011), suggesting that television viewing may contribute to depression. Because of design limitations of the available studies, it is unclear whether this effect is mediated by physical activity.

Television viewing also is associated with violence, aggressive behaviors, early sexual activity, and substance abuse (Kappos, 2007). These relationships are likely due to the content of the programming and advertising as opposed to the sedentary nature of the activity. Television viewing may affect creativity and involvement in community activities as well; however, the evidence here is very limited (Kappos, 2007). Studies with experimental designs are needed to establish a causal relationship between sedentary behavior and mental health outcomes (Kappos, 2007).

Although the available evidence is not definitive, it does suggest that sedentary activity and television viewing in particular can increase the risk for depression, anxiety, aggression, and other risky behaviors and may also affect cognition and creativity (Kappos, 2007), all of which can affect academic performance. It would therefore appear prudent for schools to reduce these sedentary behaviors during school hours and provide programming that has been shown to be effective in reducing television viewing outside of school (Robinson, 1999; Robinson and Borzekowski, 2006).

It is not surprising that physical activity improves mental health. Both physiological and psychological mechanisms explain the observed associations. Physiologically, physical activity is known to increase the synaptic transmission of monoamines, an effect similar to that of anti-depressive drugs. Physical activity also stimulates the release of endorphins (endogenous opoids) (Peluso and Guerra de Andrade, 2005), which have an inhibitory effect on the central nervous system, creating a sense of calm and improved mood (Peluso and Guerra de Andrade, 2005; Ahn and Fedewa, 2011). Withdrawal of physical activity may result in irritability, restlessness, nervousness, and frustration as a result of a drop in endorphin

levels. Although more studies are needed to specify the exact neurological pathways that mediate this relationship, it appears that the favorable impact of physical activity on the prevention and treatment of depression may be the result of adaptations in the central nervous system mediated in part by neurotropic factors that facilitate neurogenerative, neuroadaptive, and neuroprotective processes (Dishman et al., 2006). It has been observed, for example, that chronic wheel running in rats results in immunological, neural, and cellular responses that mitigate several harmful consequences of acute exposure to stress (Dishman et al., 2006). A recent study found that children who were more physically active produced less cortisol in response to stress, suggesting that physical activity promotes mental health by regulating the hormonal responses to stress (Martikainen et al., 2013).

Psychological mechanisms that may explain why physical activity improves mental health include (1) distraction from unfavorable stimuli, (2) increase in self-efficacy, and (3) positive social interactions that can result from quality physical activity programming (Peluso and de Andrade, 2005) (see also the discussion of psychosocial health above). The relative contribution of physiological and psychological mechanisms is unknown, but they likely interact. Poor physical health also can impair mood and mental function. Health-related quality of life improves with physical activity that increases physical functioning, thereby enhancing the sense of well-being (McAuley and Rudolph, 1995; HHS, 2008).

Physical activity during childhood and adolescence may not only be important for its immediate benefits for mental health but also have implications for long-term mental health. Studies have shown a consistent effect of physical activity during adolescence on adult physical activity (Hallal et al., 2006). Physical activity habits established in children may persist into adulthood, thereby continuing to confer mental health benefits throughout the life cycle. Furthermore, physical activity in childhood may impact adult mental health regardless of the activity’s persistence (Hallal et al., 2006).

Physical activity can improve mental health by decreasing and preventing conditions such as anxiety and depression, as well as improving mood and other aspects of well-being. Evidence suggests that the mental health benefits of physical activity can be experienced by all age groups, genders, and ethnicities. Moderate effect sizes have been observed among both youth and adults. Youth with the highest risk of mental illness may experience the most benefit. Although evidence is not adequate to determine the ideal regimen, aerobic and high-intensity physical activity are likely to confer the most benefit. It appears, moreover, that a variety of types of physical activity are effective in improving different aspects of mental health; therefore,

a varied regimen including both aerobic activities and strength training may be the most effective. Frequent episodes of physical activity are optimal given the well-substantiated short-term effects of physical activity on mental health status. Although there are well-substantiated physiological bases for the impact of physical activity on mental health, physical activity programming that effectively enhances social interactions and self-efficacy also may improve mental health through these mechanisms. Quality physical activity programming also is critical to attract and engage youth of all skills level and to effectively reach those at highest risk.

Sedentary activity may increase the risk of poor mental health status independently of, or in addition to, its effect on physical activity. Television viewing in particular may lead to a higher risk of such conditions as depression and anxiety and may also increase violence, aggression, and other high-risk behaviors. These impacts are likely the result of programming and advertising content in addition to the physiological effects of inactivity and electronic stimuli.

In conclusion, frequently scheduled and well-designed opportunities for varied physical activity during the school day and a reduction in sedentary activity have the potential to improve students’ mental health in ways that could improve their academic performance and behaviors in school.

Good health is the foundation of learning and academic performance (see Chapter 4 ). In children and youth, health is akin to growth. An extensive literature demonstrates that regular physical activity promotes growth and development and has multiple benefits for physical, mental, cognitive, and psychosocial health that undoubtedly contribute to learning. Although much of the evidence comes from cross-sectional studies showing associations between physical activity and various aspects of health, available prospective data support this cross-sectional evidence. Experimental evidence, although more limited for younger children, is sufficient among older children and adolescents to support the notion that children and young adults derive much the same health benefits from physical activity.

Moreover, many adult diseases have their origins in childhood. This finding, together with the finding that health-related behaviors and disease risk factors may track from childhood into adulthood, underscores the need for early and ongoing opportunities for physical activity.

Children’s exercise capacity and the activities in which they can successfully engage change in a predictable way across developmental periods. For example, young children are active in short bursts, and their capacity for continuous activity increases as they grow and mature (see Figure 3-2 ). In adults and likely also adolescents, intermittent exercise has much the same

FIGURE 3-2 Changes in physical activity needs with increasing age of children and adolescents. SOURCE: Adapted from Malina, 1991. Reprinted with permission from Human Kinetics Publishers.

benefit as continuous exercise when mode and energy expenditure are held constant. The health benefits of sporadic physical activity at younger ages are not well established. However, the well-documented short-term benefits of physical activity for some aspects of mental and cognitive health suggest that maximum benefit may be attained through frequent bouts of exercise throughout the day.

Children require frequent opportunities for practice to develop the skills and confidence that promote ongoing engagement in physical activity. Physical education curricula are structured to provide developmentally appropriate experiences that build the motor skills and self-efficacy that underlie lifelong participation in health-enhancing physical activity, and trained physical education specialists are uniquely qualified to deliver them (see Chapter 5 ). However, physical education usually is offered during a single session. Therefore, other opportunities for physical activity can supplement physical education by addressing the need for more frequent exercise during the day (see Chapter 6 ). In addition to the immediate benefits of short bouts of physical activity for learning and for mental health, developmentally appropriate physical activity during those times, along with the recommended time in physical education, can contribute to daily

energy expenditure and help lessen the risk of excess weight gain and its comorbidities. Specific types of activities address specific health concerns. For example, vertical jumping activities contribute to energy expenditure for obesity prevention and also promote bone development (via the resulting ground reaction forces), potentially contributing to lower fracture risk. Other activities contribute to prevention of chronic disease. Since different types of physical activity contribute to distinct aspects of physical, mental, and psychosocial health, a varied regimen is likely to be most beneficial overall.

The quality of physical activity programming also is critical; psychosocial outcomes and improvements in specific motor skills, for example, are likely the result of programming designed specifically to target these outcomes rather than just a result of increases in physical activity per se. These psychosocial outcomes also are likely to lead to increased levels of physical activity in both the short and long terms, thereby conferring greater health benefits. Unstructured physical activity or free play also confers unique benefits and is an important supplement to more structured opportunities. Quality physical activity programming that makes these activities attractive, accessible, and safe for children and youth of all skill and fitness levels is critical to ensure that all youth participate in these activities and can therefore derive the health benefits.

Sedentary activities, such as screen viewing and excessive time spent sitting, may contribute to health risks both because of and independent of their impact on physical activity. Thus specific efforts in school to reduce sedentary behaviors, such as through classroom and playground design and reduction of television viewing, are warranted.

In sum, a comprehensive physical activity plan with physical education at the core, supplemented by other varied opportunities for and an environment supportive of physical activity throughout the day, would make an important contribution to children’s health and development, thereby enhancing their readiness to learn.

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Ziviani, J., A. Poulsen, and C. Hansen. 2009. Movement skills proficiency and physical activity: A case for Engaging and Coaching for Health (EACH)-child. Australian Occupational Therapy Journal 56(4):259-265.

Physical inactivity is a key determinant of health across the lifespan. A lack of activity increases the risk of heart disease, colon and breast cancer, diabetes mellitus, hypertension, osteoporosis, anxiety and depression and others diseases. Emerging literature has suggested that in terms of mortality, the global population health burden of physical inactivity approaches that of cigarette smoking. The prevalence and substantial disease risk associated with physical inactivity has been described as a pandemic.

The prevalence, health impact, and evidence of changeability all have resulted in calls for action to increase physical activity across the lifespan. In response to the need to find ways to make physical activity a health priority for youth, the Institute of Medicine's Committee on Physical Activity and Physical Education in the School Environment was formed. Its purpose was to review the current status of physical activity and physical education in the school environment, including before, during, and after school, and examine the influences of physical activity and physical education on the short and long term physical, cognitive and brain, and psychosocial health and development of children and adolescents.

Educating the Student Body makes recommendations about approaches for strengthening and improving programs and policies for physical activity and physical education in the school environment. This report lays out a set of guiding principles to guide its work on these tasks. These included: recognizing the benefits of instilling life-long physical activity habits in children; the value of using systems thinking in improving physical activity and physical education in the school environment; the recognition of current disparities in opportunities and the need to achieve equity in physical activity and physical education; the importance of considering all types of school environments; the need to take into consideration the diversity of students as recommendations are developed.

This report will be of interest to local and national policymakers, school officials, teachers, and the education community, researchers, professional organizations, and parents interested in physical activity, physical education, and health for school-aged children and adolescents.

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Physical Education and Its Importance to Physical Activity, Vegetable Consumption and Thriving in High School Students in Norway

Associated data.

Data supporting reported results can be found on the following link: https://teams.microsoft.com/_#/school/files/General?threadId=19%3A00faa60f3ab64020b836a1c964c56962%40thread.skype&ctx=channel&context=PYD%2520Database&rootfolder=%252Fsites%252FTEAM_PYDCrossNational_Project%252FShared%2520Documents%252FGeneral%252FPYD%2520Database (accessed on 18 August 2021).

Earlier research indicates that physical education (PE) in school is associated with positive outcomes (e.g., healthy lifestyle, psychological well-being, and academic performance). Research assessing associations with resilience and thriving indicators, such as the 5Cs of Positive Youth Development (PYD; competence , confidence , character , caring , and connection ) is limited and more so in the Norwegian context. The aim of the present study was to investigate associations between PE grade (reflecting students’ effort in theoretical and practical aspects of the subject) and the 5Cs as well as healthy behaviors (physical activity (PA), fruit and vegetable consumption), using cross-sectional data collected from 220 high school students in Norway ( M age = 17.30 years old, SD = 1.12; 52% males). Results from structural equation modelling indicated positive associations between PE grade and four of the 5Cs ( competence , confidence , caring , and connection ; standardized coefficient: 0.22–0.60, p < 0.05) while in logistic regressions, a unit increase in PE grade was associated with higher likelihood of engaging in PA and vegetable consumption (OR = 1.94; 95% CI = 1.18–3.18 and OR = 1.68; 95% CI = 1.08–2.63, respectively). These significant findings suggest the need for policies and programs that can support effective planning and implementation of PE curriculum. However, further research is needed to probe into the role of PE on youth health and development with representative samples and longitudinal designs.

1. Introduction

The positive and protective effects of physical activity (PA), such as enhanced physical health, psychological well-being, increased concentration, academic performance, and reduced feelings of depression and anxiety, have been well documented in earlier studies [ 1 , 2 , 3 ]. Physical education (PE) is taught as a subject in many countries around the world, but it also incorporates aspects of PA within the school context, because of the different indoor and outdoor activities students engage in during PE sessions. Indeed, Mooses and colleagues [ 4 ] found PE to significantly increase daily moderate to vigorous PA alongside reducing sedentary time among schoolchildren. In addition, Tassitano and colleagues [ 5 ] observed a positive association between enrollment in PE sessions and several health-related behaviors including physical activity and fruit consumption.

In many schools, students’ efforts in PE are captured in the grade they receive on the subject. Thus, higher grades in PE would indicate greater efforts and achievement in the physical activities engaged in, which in turn can lead to the promotion of outcomes related to health and development as indicated in earlier studies [ 1 , 2 , 3 ]. The present study seeks to determine whether this is the case in high school students in Norway.

1.1. Physical Education in the Global and Norwegian Contexts

In basic terms, physical education has been described as “education through the physical”. Consistent with United Nations Educational, Scientific and Cultural Organization, PE embraces terms, such as “physical culture”, “movement”, “human motricity”, and “school sport”, and refers to a structured period of directed physical activity in school contexts [ 6 ]. A PE curriculum usually features activities such as team and individual games and sports, gymnastics, dance, swimming, outdoor adventure, and track and field athletics [ 6 ]. By engaging in a variety of physical activities, students are taught physical, social, mental, and emotional skills to empower them to live an active and healthy lifestyle. PE is also an arena where students can develop and practice skills related to collaboration, communication, creativity, and critical thinking [ 7 ].

In a world-wide survey of physical education that involved 232 countries (and autonomous regions), 97% of the countries were found to have either legal requirements for PE within their general education systems or PE was a general practice at some ages of the schoolchildren or phases of compulsory schooling [ 6 ]. The number of PE lessons that were taught in schools across the countries varied from 0.5 to 6.0 per week and from 16 to 46 weeks per year during compulsory education. Country variation depended greatly on the mindset held about the importance and relevance of the subject in the school curricula.

A European Commission report on physical education and sport at school in Europe indicates that while about 50% of the educational systems have national strategies to support the development of PE and PA, two-thirds have large-scale schemes assigned to these activities [ 8 ]. With activities that include athletics, dance, health and fitness, gymnastics, games, outdoor and adventure, swimming, winter sports, and others, the goals of European countries have been to promote the development of pupils and students in the physical, personal, and social domains [ 8 ].

As in many European countries, PE is one of several subjects taught to pupils and students in compulsory education in Norway (i.e., 6–16-year-olds in primary and lower secondary education). The PE curriculum has both practical and theoretical components. In both components of the curriculum, students are introduced to organized physical activities and spontaneous play in varied environments, in a wide range of sports, dance and other movement activities, and in outdoor life, which allows them to orient and spend time in nature in different seasons as well as being an aspect of exercise and lifestyle that deals with the effect of physical activity on health. In high schools, students receive a total of 168 h of PE lessons during their 3-year education, where in addition to sports activities, outdoor life, and lessons on exercise and lifestyle, they receive education in physical motor activities that go beyond traditional sports activities. Moreover, students at this level of education have the possibility to combine PE with active participation in competitive sports [ 9 ].

PE lessons in Norway focus on providing students with challenges and courage to enable them to stretch their own boundaries, in both spontaneous and organized activities. In addition, it is anticipated that students will experience joy, mastery and inspiration by participating in a variety of physical activities, which will eventually help them to develop self-esteem, self-understanding, positive perception of the body and positive identity. Furthermore, the social aspects of the physical activities are intended to create an arena where students can exercise fair play and respect for each other [ 9 , 10 ]. All these effects are positive outcomes that tend to signify several components of what has been referred to as the 5Cs of PYD ( competence , confidence , character , caring, and connection ) [ 11 ] and the ability to develop healthy behaviors, thus supporting health as defined by the World Health Organization. In 1948, the World Health Organization [ 12 ] defined health as “a state of complete physical, mental and social well-being and not merely the absence of disease or infirmity” (p. 100). PE’s role in facilitating health and development will thus touch on WHO’s three dimensions of health.

The current focus of the Norwegian PE curriculum is a result of changes made to the curriculum in 2012, due among others to students and teachers’ dissatisfaction with the stress emanating from the expectations attached to sports achievements and physical performance abilities as well as the observation and measurement the teachers had to undertake to grade students’ abilities. With the present curriculum, it is the effort made by students (i.e., the attempts made to use the acquired knowledge and capabilities to reach developmental goals and not necessarily the attained progress) that is considered as relevant [ 13 ]. Thus, a high grade in PE subject will not only indicate a form of academic achievement, but it will also signify students’ efforts and experience in a variety of physical activities and their knowledge on how these activities can promote positive developmental outcomes, such as health, self-development, and identity [ 14 ].

1.2. Positive Youth Development and the 5Cs

Positive Youth Development is a line of research and a developmental framework that focuses on the identification and promotion of youth strengths [ 15 , 16 ], and the equipping of youth toward becoming productive members of their society [ 16 ]. PYD suggests that all young people have strengths and as such are potential resources to their own development and that of the society they are a part of. In addition, PYD proposes that all youth contexts, such as home, school and the local community, have human and material resources that youth can have access to in their interactions with significant others in these contexts [ 17 ]. In PE sessions, these contextual resources will be the support from peers and teachers, the opportunities created for students to develop resilience, competences and mastery, the boundaries students will have to respect as well as the expectations to be met. Youth strengths will be the personal interest, skills, and abilities that students bring to the PE sessions.

Within PYD, the 5Cs are viewed as a product of the alignment between youth strengths and contextual resources [ 15 ]. Accordingly, the dynamic interaction that ensues between an active, engaged, and competent person and their receptive, supportive, and nurturing ecologies in the context of varying degrees of risk and adversity will lead to a process referred to as adaptive developmental regulations [ 11 , 15 , 18 ], where youth can be resilient, thrive and develop to their full potential. Thriving means youth are scoring high on the 5Cs. The 5Cs include competence (which reflects the positive views of an individual’s action in domains, such as academic, social, cognitive and vocational); confidence (which relates to the individual’s sense of mastery and purpose for the future, a positive identity and self-efficacy); character (which denotes one’s integrity, moral commitment, and respect for societal and cultural rules); caring (which indicates one’s sense of empathy and sympathy for others); and connection (which reflects the bidirectional exchanges and healthy relations between the individual and friends, family, school, and community). Within the PYD framework, the 5Cs typically reflect thriving and positive development, but also resilience (in contexts where there are high levels of risk and adversity) among young people [ 15 , 18 ]. PYD proposes that youth who are thriving are put on a life trajectory towards an “idealized adulthood” [ 19 ]. In addition, youth who are resilient and thriving are more likely to contribute to their own development as well as to the development of their society [ 15 ].

1.3. Earlier Research on Positive Youth Development, Healthy Behaviors and Physical Education

Research on the relationship between grade in PE (which reflects students’ participation in PE sessions) and the 5Cs of PYD is limited, although earlier studies have recounted several positive outcomes of PE in schools. In one study that investigated PYD-related outcomes in the contexts of PE, Holt et al. [ 20 ] found in a qualitative study of 8 teachers and 59 children at an inner-city school in Canada that PE activities engaged in tended to promote developmental outcomes, such as empathy and healthy relationships between students. In addition, PE activities became an arena where teachers considered students’ input to the PE activities and created boundaries and procedures for expected behaviors.

Furthermore, Bailey [ 1 ], in a review article, summarized several positive and profound benefits of PE that included physical health, healthy lifestyle, psychological well-being, social skills and improved academic performance. These benefits were more probable in contexts where there were positive experiences of the PE activities, enjoyment, efforts made to engage all students as well as when teachers and coaches were committed and were equipped with the necessary skills. In another literature review on the impact of PE and sport on educational outcomes, Stead and Nevill [ 21 ] found that increased physical education, physical activity or sport tended to maintain or enhance academic achievement. The authors also found a positive association between physical activity and aspects of mental health, such as self-esteem, emotive well-being, spirituality, and future expectations. Moreover, Stead and Nevill [ 21 ] observed that the implementation of extra organized physical activity, as little as 10 min into the school day, tended to improve classroom behavior. These earlier studies support the important role of PE on health (including the physical, mental, and social dimensions) and positive development in youth.

As for healthy behaviors and their associations with PE, Mayorga-Vega and colleagues [ 22 ] conducted a study among 158 students in a Spanish high school and found that students had greater physical activity levels and lower levels of sedentary behaviors during PE days compared to non-PE days and weekends. In a much larger sample of 4210 high school students in Brazil, Tassitano et al.’s [ 5 ] assessment of the role of PE enrollment on several health behaviors revealed, among others, positive associations of enrollment in PE classes with physical activity and fruit consumption, as well as a negative association with drinking of sugar-sweetened beverages. In a longitudinal study of Canadian adolescents, Wiseman and Weir [ 23 ] investigated PE rating among other subjects alongside the importance of PE for PA levels and several health variables over a two-year period. Their results indicated that most of the participants (78%) preferred PE over other subjects, and that preferring PE was associated with higher PA levels, lower BMI, and higher self-esteem. Thus, while earlier research supports the predictive role of PE on youth development and healthy behaviors, the evidence regarding the importance of PE to the 5Cs of PYD is unclear because of limited research.

1.4. Aims of the Present Study

Research on the 5Cs of PYD has usually involved American youth [ 11 , 24 ] although research featuring non-American samples is growing [ 25 , 26 ]. Moreover, while the effects of PE on youth health and development have been widely studied, a literature search did not return any study that had assessed the relation between PE and the 5Cs in the Norwegian context. Several studies have hinted how activities engaged in during PE can be used to foster positive development. For example, Mandigo et al. [ 27 ] described how quality PE activities can be used to promote positive development and peace education among schoolchildren in a developing country. More specifically, the authors outlined various behaviors in the physical, intellectual, psychological, and social domains that physical educators can instill in schoolchildren to foster the 5Cs of PYD and peaceful interactions. Holt and colleagues [ 20 ] also described how strategies, such as setting of clear boundaries and allowing inputs from schoolchildren, and the teacher being a PE specialist, could facilitate positive youth development. Thus, in line with these earlier PYD studies, PE can be an arena where youth development as well as health (as proposed by WHO) are promoted.

In the present study, the aim is to examine the link between grade in PE and positive outcomes reflected in the 5Cs of PYD. A second aim is to study the association between PE grade and healthy behaviors, such as PA during leisure time and the consumption of fruit and vegetables. With the goal of the Norwegian PE curriculum to promote health, self-development and identity among others, grade in PE reflecting attained knowledge, participation and efforts invested in various physical activities should be associated with the 5Cs. Thus, as a hypothesis, students with higher PE grades are also expected to report higher scores on the 5Cs. Like the 5Cs, positive associations are hypothesized between PE grade and healthy behaviors. If positive associations are found between PE, the 5Cs and healthy behaviors, PE can be considered as an avenue to instill competencies that can have implications for students’ health, thriving, and resilience. Earlier studies suggest that boys engage in PA more often than girls, and PA tends to decrease with age [ 28 ]. Parents’ educational level has also been found to be positively related to the 5Cs [ 26 ]. Hence, gender, age, and parents’ education were accounted for in the assessment of the influence of PE grade on the 5Cs and healthy behaviors.

2. Materials and Methods

2.1. sample.

The current study forms part of a larger international project on positive development among youth and emerging adults, where the general goal is to assess how youth strengths and contextual resources align to foster thriving and youth contribution to societal development [ 29 ]. For the present study, cross-sectional data were collected from 220 students in four high schools located in Eastern and Western Norway. About 52% of the participants were boys and the age range was between 16 and 20 years ( M = 17.30, SD = 1.12). Almost 83% reported that the highest level of education of their father was postsecondary, while 87% did the same for their mother’s education.

2.2. Measures

2.2.1. physical education grade.

Participants self-reported their current academic grade (1 to 6) on physical education. A grade of 1 represents minimum knowledge and effort invested during PE sessions while a grade of 6 represents great knowledge and maximum invested effort in PE sessions.

2.2.2. The 5Cs of PYD

To assess the 5Cs, Geldhof and colleagues’ [ 11 ] short version of the PYD questionnaire, consisting of 34 items, was used. Samples of the items used in measuring the 5Cs include: “I am just as smart as others my age” ( competence , 6 items); “I really like the way I look” ( confidence , 6 items); “I usually act the way I am supposed to” ( character , 8 items); “When I see someone being exploited I want to help them” ( caring , 6 items); and “I am a helpful and important family member” ( connection , 8 items). Responses were measured on a 5-point Likert scale, ranging from 1 (Strongly Disagree) to 5 (Strongly Agree), for example, where a higher score indicated a higher experience of the C-item in question. The psychometric properties of the 5Cs scale have been mostly assessed in U.S. samples [ 11 , 24 ] but also in some non-U.S. samples [ 25 , 26 ].

2.2.3. Healthy Behaviors

Items measuring healthy behaviors (physical activity, fruit and vegetable consumption) were adopted from the Search Institute’s [ 30 ] survey on attitudes and behaviors. Participants indicated 0 (No) or 1 (Yes) to the following items: “I engage in physical activity (for at least 30 min) twice or more per week”, “I eat at least one serving of fruit every day” and “I eat at least one serving of vegetables every day”. Spearman correlation among the three healthy behaviors ranged from 0.25 to 0.37.

2.2.4. Demographic Variables

Data were also collected on gender (boy or girl), age and mother and father’s educational level (five levels of education: 1 (no education), 2 (primary school), 3 (high school), 4 (technical or vocational school), and 5 (university)). The demographics were treated as control variables in the data analysis.

2.3. Procedure

Data collection took place in May–August 2019. Convenience sampling was used to select four schools located in the Eastern and Western parts of Norway. The heads of the conveniently selected schools were contacted via e-mail, with a request to participate in the study and an information letter about the purpose of the study. After agreeing to participate, the heads of schools were sent informed consent forms, developed in accordance with the NSD (Norwegian Centre for Research Data) guidelines, which they were asked to sign and send back. Once that was done, teachers from the four schools who agreed to conduct the survey with their students were sent the questionnaire via email. Informed consent was sought from students prior to the data collection, which took place during school hours over the schools’ internal web system. NSD (Norwegian Centre for Research Data) approved the study (51708/3/IJJ), while Semantix Translations Norway AS, Oslo, Norway, a company that specializes in interpretation services, translated the questionnaire from English to Norwegian using double-checking methods and translation experts in the relevant field of research to ensure preservation of meaning.

2.4. Data Analysis

G*Power 3 [ 31 ] was used to conduct a power analysis to determine the sample size that will allow for the assessment of meaningful associations and the detection of effect sizes (small, medium, or large). Using a two-tailed test with the 5 independent variables (PE grade and the four demographic variables (gender, age, father’s education and mother’s education)), and an alpha value of 0.05, the results indicated that with a power of 0.80, sample sizes of 395, 55, and 25 were needed to detect effect sizes of 0.02 (small), 0.15 (medium), and 0.35 (large), respectively. Reaching the study’s sample size of 220 meant that medium to large effect sizes can be detected in the statistical analyses.

Descriptive and correlation analyses were performed using IBM SPSS Statistics for Windows, version 25, while all other analyses were carried out using Mplus version 8 [ 32 ]. Most participants (80%) were missing only 3 cases or less, while 59% had full data. The analyses in Mplus were conducted with the Maximum likelihood estimation, an estimation method used to handle missing cases. The method works by estimating a likelihood function for each case based on the variables present in the dataset such that all the available data are used.

Descriptive analyses were conducted to assess the pattern of study variables: the demographics, PE grade, the 5Cs of PYD and the three healthy behaviors. Confirmatory factor analysis (CFA) was performed on the items measuring the 5Cs to verify the factorial structure of the scale. Chi-square tests and indices, such as the Tucker Lewis Index (TLI; acceptable above 0.90), the Root Mean Square Error of Approximation (RMSEA; acceptable below 0.08), and Comparative Fit Index (CFI; acceptable above 0.90) [ 33 , 34 ]) were used to evaluate model fit. To test the hypothesis that higher scores in PE will be associated with higher scores in the 5Cs, structural equation modelling (SEM) analysis was carried out. In preliminary analyses, the linearity and normal distribution of the 5Cs as dependent variables were determined, with skewness and kurtosis falling within the acceptable range of −2 to +2 and −7 to +7, respectively for SEM analysis [ 35 ]. Finally, the hypothesis that higher scores in PE will be associated with higher odds of the healthy behaviors was tested using logistic regressions due to the binary response categories of the healthy behavior variables. In both SEM and logistic regression, the demographic variables: gender, age, and father’s and mother’s educational background were controlled for.

3.1. Descriptive Analysis

In Table 1 , a frequency analysis of PE grade showed that about 96% of the participants reported grades between 4 and 6. In the Norwegian high school system, a grade of 1 is the lowest, while 6 is the highest a student can earn in a subject. For the 5Cs of PYD, high Cronbach’s alphas, indicating high internal consistencies (ranging from 0.85–0.93) were estimated for all the Cs. The frequency distribution of the three healthy behaviors revealed that most of the participants (about 82%) engaged in PA for at least 30 min twice or more per week, while 57% and 70% consumed at least one serving of fruit and vegetable per day, respectively ( Table 1 ).

Descriptive statistics and reliability coefficients for study variables among Norwegian youth.

Furthermore, descriptive analysis of the 5Cs showed that the highest mean score was registered for caring ( M = 4.29, SD = 0.78), followed by character and then connection . Competence had the lowest mean score ( M = 3.65, SD = 0.86). Thus, on average, participants’ responses on the 5Cs suggested moderate to relatively high levels of the PYD outcomes. The statistically significant correlations between PE grade and the 5Cs (mean scores) were weak to moderate, ranging from 0.17 to 0.55. In addition, the correlation between PE grade and the healthy behaviors were weak but statistically significant (0.19–0.25). Finally, several significant but weak correlations were observed between the 5Cs and the healthy behavior variables as well as between the demographic variables, the 5Cs and the healthy behavior variables ( Table 2 ).

Correlation analyses of demographic variables, physical education grade, the 5Cs of PYD, and healthy behaviors.

Note. * p < 0.05; ** p < 0.01.

3.2. CFA of the 5Cs of PYD and Structural Equation Modelling of PE Grade and the 5Cs

Prior to the assessment of the associations between PE grade and the 5Cs, confirmatory factor analysis (CFA) was conducted on the 34 items of the 5Cs to determine the factorial structure of the scale. An initial CFA of the items, where 14 pairs of same-facet items (in competence , confidence , character and connection ) were allowed to correlate, yielded a poor model fit: χ 2 (500, N = 194) = 998.075, p < 0.001, RMSEA = 0.072, CFI = 0.872, TFI = 0.857. An examination of the modification indices revealed cross-loadings of four items, two items regarding social competence for competence , one item on social conscience for character and another on caring . In addition, the modification indices indicated correlations among one pair of same-construct items (i.e., confidence ) and two pairs of different-construct items, one between competence and connection , and the other between confidence and character . After eliminating cross-loading items and including the correlations, an adequate model fit was attained in a second CFA: χ 2 (378, N = 194) = 646.879, p < 0.001, RMSEA = 0.061, CFI = 0.917, TFI = 0.905. The factor loadings for all 5Cs in this new CFA were adequate, ranging from 0.54 to 0.91. Correlations among the latent factors of the 5Cs were between 0.32 and 0.88.

In Table 3 , having controlled for demographic factors (i.e., gender, age, and parents’ educational background), findings from the structural equation modelling revealed significant associations between PE grade and all the 5Cs of PYD except for character . Not surprisingly, the strongest association was between PE grade and competence (standardized coefficient of 0.60), both largely reflecting students’ competence. The standardized coefficients for confidence and connection were 0.36, and 0.37, respectively, while for caring the coefficient was 0.22. Thus, higher scores in PE were significantly associated with higher scores in the 5Cs besides character . As for the demographic variables, only gender was significantly related to caring in the SEM analysis (standardized coefficient of 0.36), where girls scored higher than boys.

Structural equation model of physical education grade and the 5Cs of PYD.

Note. PE—Physical education; a Controlled for gender, age, father’s education and mother’s education; * Standardized coefficient. Italics and bold show significant levels less than 0.05.

3.3. Logistic Regression Analyses of Physical Education and Healthy Behaviors

For the associations between PE grade and healthy behaviors, logistic regression models were analyzed because of the binary response categories of the behaviors ( Table 4 ). After controlling for the demographic variables, a unit increase in PE grade was associated with a 94% higher likelihood of engaging in PA (OR = 1.94; 95% CI = 1.18–3.18), and a 68% higher likelihood of vegetable consumption (OR = 1.68; 95% CI = 1.08–2.63), that is, when all other variables in the models were held at a constant. Thus, PE grade was significantly related to higher odds of PA and vegetable consumption, while the association with fruit consumption was not significant. None of the demographic variables were significantly related to the healthy behavior variables in the logistic regression analyses.

Associations between physical education (PE) and healthy behaviours: logistic regression analysis.

Note. PE—Physical education; B—Unstandardized coefficient; S.E.—Standard Error; Sig—Significance level; OR—Odds Ratio; CI—Confidence Interval.

4. Discussion

The aim of the present study was to investigate the associations of PE grade with the 5Cs of PYD and healthy behaviors. As hypothesized, positive associations were observed between PE grade and four of the 5Cs ( competence , confidence , caring , and connection ) after adjusting for gender, age, and father’s and mother’s educational background. In contrast, although there was an indication that character was associated with PE grade, this association was not statistically significant in the SEM analysis. For the associations between PE grade and healthy behaviors, while logistic regression analyses showed higher odds of engagement in PA and vegetable consumption with every unit increase in PE grade, no such association was found for fruit consumption. Thus, the hypotheses were confirmed, although not for the association of PE grade with character and fruit consumption. That PE was found to be largely associated with the 5Cs and healthy behaviors is consistent with earlier findings that have supported the significant role of PE sessions on positive outcomes reflecting WHO’s different dimensions of health (physical, mental, and social) [ 1 , 21 ].

The current finding that PE grade was strongly related to competence was no surprise, as both connote a form of academic competence. In the present study, competence as one of the 5Cs was measured as competence in the academic and physical domains. Thus, PE grade was not only related to academic competence or cognitive abilities, but also to physical competence in sports and athletic activities. Earlier research among German students that supports the current findings reported a positive association between PE and cognitive skills measured by grades in German and mathematics [ 36 ], while findings of a review article also indicated that increasing the amount of time dedicated to PE and sports was in many instances associated with academic performance [ 1 ]. The goal of the Norwegian PE curriculum to enable students to develop mastery in the skills needed to undertake a variety of physical activities [ 9 ] can therefore be important not just for the grade in PE but for the general academic competence of students as well.

In addition to being associated with competence , PE grade was associated with confidence , caring and connection. Accordingly, students who scored high in PE were also more likely to report indicators of thriving and positive development, associations that have been confirmed in a related study on the link between participation in sport camps and the 5Cs of PYD that were captured as two factors (pro-social values and confidence/competence) [ 37 ]. Moreover, Bailey [ 1 ] in a review, reported on how PE and sports in schools can provide a favorable environment for social development, a finding that largely corroborates the current results on the significant link between PE and connection (signifying healthy social relations at home, school, and local community). Indeed, an important aim of the Norwegian PE curriculum among others is to create a social arena for fair play and respect between students [ 9 , 10 ]. However, character (reflecting the integrity and moral compass of youth) was the only thriving indicator that was not associated with PE grade, neither in zero-order correlation nor in multivariate analysis. It is possible that the alignment between youth strengths and contextual resources that facilitate the 5Cs of PYD in PE sessions predicts some of the Cs better than others. This assertion will need to be probed into in future research.

Furthermore, PE grade was related to healthy behaviors, such as PA and vegetable consumption, but not fruit consumption. Earlier research among students attending a Spanish high school associated participation in PE with greater PA levels and lower levels of sedentary behaviors during PE days compared to non-PE days and weekends [ 22 ]. Enrollment in PE activities among high school students in Brazil has been found to be positively related to healthy behaviors, such as PA and fruit consumption, as well as negatively related to drinking of sugar-sweetened beverages [ 5 ]. Wiseman and Weir [ 23 ] also found among Canadian high school students that preferring PE over other school subjects was associated with higher PA levels, lower BMI, and higher self-esteem. Although it was PE grade that was assessed in the current study, the grade reflects students’ participation in both theoretical and practical components of the Norwegian PE sessions. Thus, the current finding on the positive association between PE grade and healthy behaviors is largely in line with earlier findings. In summary, PE sessions reflected in the grade of students were associated with positive youth developmental outcomes, such as thriving (the 5Cs) and healthy behaviors, outcomes that tend to reflect all three dimensions of health (physical, mental, and social) as defined by the World Health Organization.

In SEM and logistic regression, the demographics did not appear to play an important role on the 5Cs and healthy behaviors, as a significant association was only observed between gender and caring , with girls reporting higher scores than boys. This finding is in line with earlier research that found similar associations in upper secondary and university students in Spain [ 38 ] and is often attributed to gender socialization, where boys are taught to be tough and girls caring. In future studies, the role of gender and other demographics are worth investigating to ascertain their effects and place in intervention programs.

4.1. Limitations

The present study has some limitations that need to be considered in the interpretation of the findings. First, the relationships between PE grade and the positive youth developmental outcomes may not indicate causation due to the cross-sectional design of the current study. While the present and earlier findings suggest a positive influence of PE on youth development and healthy behaviors, it is also possible that high levels of the thriving indicators ( competence , confidence , caring and connection ) led to more effort in PE sessions, and consequently, high grade in the subject. In addition, it is likely that students who participate in healthy behaviors such as PA and vegetable consumption will also perform better in PE sessions. Looking at these relationships within a longitudinal design will shed more light on both the developmental trajectories and relations between PE participation and positive youth outcomes.

Second, while there is no reason to believe that youth will be deceptive in the report of their grade and competencies, it is still likely that their self-report responses were affected by social desirability bias, where they tended to over-report their PE grades, for example. In future studies, students’ actual grades provided by teachers can be one method to address the limitation associated with self-report responses and the associated social desirability bias. Third, the binary response categories (Yes/No) of the healthy behaviors did not allow much variation among the behaviors to be assessed. Moreover, although the measures represented general assessment of PA and fruit and vegetable consumption, they did not adequately reflect the global recommendations of the healthy behaviors. This is a limitation that can be addressed in future studies with better instruments that allow for more variations as well as assessment of the recommended amounts and levels of the healthy behaviors. Fourth, the items measuring the 5Cs of PYD were created with US samples, and although the scale was largely validated with the Norwegian sample, there were some items that cross-loaded onto different factors. In addition, relatively high correlations were found among some of the measures, for example between competence and confidence . Thus, it is possible that some items of the 5Cs did not adequately capture or make a distinction between the thriving indicators in Norwegian students. These shortcomings can be a topic of investigation in future studies using qualitative methods.

Finally, although the power analysis indicated that the sample size of 220 was enough to detect medium to large effect sizes in the relationships being studied, a larger sample could provide more robust findings. Besides, the participating schools and thus the students involved in the current study were selected through convenience sampling, thus limiting the extent to which the present findings can be generalized to the whole youth population in Norway. Future studies that use a more representative and inclusive sample reflecting youth from different geographic locations, diverse ethnicities and other backgrounds will be more effective in generating findings that are representative of the Norwegian youth population.

4.2. Implications for Research, Policy, and Practice

Despite the limitations, the current study has implications for research, policy, and practice. In terms of research, the validation of the 5Cs of PYD scale among high school students in Norway adds to the limited research of the 5Cs in Norway and paves the way for further research of the thriving indicators among youth in the Norwegian and other similar Scandinavian and European contexts. Additional research on the 5Cs can also eventually lead to a more refined scale that includes items unique to the Norwegian, Scandinavian or European context. In addition, future studies on PE and the 5Cs can assess the level of risk and adversity in the contexts in which youth are interacting. This will enable the assessment of not only thriving, but resilience as well.

As for policy, the fact that PE grade is related to thriving and healthy behaviors suggests that the Norwegian PE curriculum is important to the promotion of the positive development of the youth, and, possibly, resilience. These results should make the effective implementation of PE curriculum in all schools a priority on the Norwegian political agenda at both the national and community or school level. This way, young people across gender, socio-economic statuses, ethnicities, and other backgrounds can be reached and empowered with the necessary physical, cognitive, and psychosocial skills and competences that are associated with the array of activities taught in PE sessions. Moreover, the current findings of the significant role of PE can inform strategies used in PE curricula in other Scandinavian and European countries. In line with a European Commission report [ 8 ], although all European countries acknowledge the importance of PE at school, only two-thirds of the educational systems had large-scale national initiatives to support the promotion of PE and PA. Indeed, as implied in the current findings, the goal of European countries to facilitate the physical, personal and social development of pupils and students can only be realized when PE curricula are planned and implemented effectively.

There are some practical implications of the current findings as well. With the significant associations between PE grade, the 5Cs of PYD (indicating thriving indicators), and healthy behaviors, it is important that during PE sessions, efforts are made to engage all students in activities that can create positive experiences, enjoyment and mastery as outlined in the PE curriculum. In the curriculum, there is also a focus to provide students with challenges that can enable them to participate actively in both spontaneous and organized activities as well as arenas where students can exercise fair play and respect for each other. Efforts made to implement all these aims in the PE sessions will not only produce healthy, thriving, and resilient youth but, as proposed by PYD, the efforts would also mean a healthy transition into adulthood for the youth.

5. Conclusions

Positive effects of PE participation have been well documented in earlier studies. The current study adds to these benefits with findings that suggest that PE grade reflecting participation in PE is significantly related to thriving indicators, such as competence , confidence , caring and connection (4 out of the 5Cs of PYD), as well as healthy behaviors such as PA and vegetable consumption. These findings support the importance of PE sessions to the healthy development of youth and suggest that policies and programs at the national and local levels that ensure the effective implementation of a PE curriculum in school would be promoting developmental outcomes that align with the dimensions of health outlined by the World Health Organization. However, more research needs to be carried out with adequate measurement of healthy behaviors and representative samples to ascertain the facilitating role of PE sessions on youth health, thriving, and positive development, but also resilience in risk and adverse contexts of youth, as this can secure a life trajectory towards an idealized adulthood for all youth.

Acknowledgments

I would like to acknowledge Maria Bøhlerengen for coordinating the data collection and the youth participants for their engagement in the present study.

This research received no external funding.

Institutional Review Board Statement

The study was conducted according to the guidelines of the Declaration of Helsinki and approved by the Institutional Review Board (or Ethics Committee) of NSD—Norwegian Centre for Research Data, Norway (protocol code 51708/3/IJJ and 18 July 2017).

Informed Consent Statement

Informed consent was obtained from all subjects involved in the study.

Data Availability Statement

Conflicts of interest.

The author declares no conflict of interest.

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