boolean search literature review

Conducting a Literature Review

• Getting Started
• Developing a Question
• Searching the Literature
• Identifying Peer-Reviewed Resources
• Managing Results
• Analyzing the Literature
• Writing the Review

Need Help? Ask Your librarian!

Search Strategies

• Boolean Operators

Once you have identified the key concepts of your research question (see "Developing a Question"), you can use those concepts to develop keywords for your search strategy. The following tips and techniques will help you design a precise and relevant search strategy.

Keywords are any words you might use to search the record of an article, book, or other material in library databases. The database searches through the metadata (such as title, authors, publication, abstract, etc.) to find resources that contain the word you searched, and may also search through the full text of the material.

Keywords are most successful when you're searching for the words that the authors use to describe the research topic, as most databases will search for those specific words within the record of the article. To increase your chance of returning relevant results, consider all of the words that  might  be used to describe the research you're trying to find, and try some of these out in sample searches to determine which words return the best results.

Search Tips - Keywords

• Search for singular and plural terms together: (physician OR physicians)
• Search for both the American and British spelling of words: (behavior OR behaviour)
• Search for synonyms of terms together: (teenager OR adolescent)
• Search for phrases inside of quotation marks: ("young adult")

Use Boolean operators to combine keywords for more precise search results. 

AND - If the term must be included in your search:

influenza AND vaccine

OR - If terms are interchangeable, i.e. synonyms. Place OR'd terms within parentheses:

(influenza OR flu) AND vaccine

NOT - If a term should not be included in your search. This Boolean operator is rarely necessary for literature reviews.

(influenza OR flu) AND vaccine NOT H1N1

Note how we've used parentheses in the examples above. Search strings like these are similar to mathematical equations, where you perform the actions within the parentheses before proceeding from left to right to run the search. For example, using the search [(influenza OR flu) AND vaccine] will find results that have a term relating to influenza/flu, as well as the term vaccine.

If we moved the parentheses, it would be a very different search. [influenza OR (flu AND vaccine)] will provide results that use the term influenza, as well as results that use both the terms flu and vaccine. This means you would get results having to do with influenza but perhaps nothing to do with vaccination. 

Here are a few examples of how this search would be different depending on the arrangement of booleans and keywords. The area highlighted in pink represents the search results that would be returned with this search.

Truncation allows you to quickly include all variations of a word in your search. Use the root of the keyword and add an asterisk (*). For example:

nurs* = nurse, nurses, nursing, nursery

IMPORTANT: Notice that "nursery" is also retrieved in the above search. Truncation will save you from having to include a large number of synonyms, but it will also add a certain number of irrelevant results. You can limit this effect by using the NOT Boolean operator, i.e. NOT nursery.

Wild cards allow you to replace a letter in a keyword to retrieve all variations of the spelling. For example:

p?ediatric = pediatric, paediatric

Free-Text vs. Thesaurus Searching

While you can search any word as a keyword, databases also contain an official list of the terms they use to describe the subject of each article, called Subject Headings. You can look up Subject Headings in the thesaurus of the database, using the thesaurus's search box to pull up the recommended Subject Heading for a given keyword. When searching specifically for Subject Headings, the database will only search the Subject Headings field within the record of each article (ie, not the title, abstract, etc.). This is a much more targeted method of searching, and is an excellent addition to your search strategy. 

A strong search strategy will use both free-text (keyword) searching and thesaurus searching, to ensure that all relevant articles have been retrieved by the search. The lists below outline the strengths and weaknesses of both types of search strategies.

Free-Text Searching

• Natural language words describing your topic
• More flexible search strategy - can use any term in any combination
• Database looks for keywords anywhere in the record - not necessarily connected together
• May yield too many or too few results
• May yield many irrelevant results

Thesaurus Searching

• Pre-defined "controlled vocabulary" words used to describe the content of each item in a database
• Less flexible search strategy - need to know the exact controlled vocabulary term
• Database looks for subjects only in the subject heading or descriptor field, where the most relevant words appear
• If too many results, you can use subheadings to focus on one aspect of a broader topic
• Results are usually very relevant to the topic

MIT Libraries. Database Search Tips: Keywords vs. Subjects. https://libguides.mit.edu/c.php?g=175963&p=1160804

Each database has their own thesaurus. You will need to adapt your search strategy for each database to take advantage of their unique thesaurus.

PubMed uses MeSH terms (Medical Subject Headings). You can learn more about finding and using MeSH terms here:

• The Basics of Medical Subject Headings (MeSH) in MEDLINE/PubMed: A Tutorial

CINAHL uses CINAHL Headings. You can learn more about finding and use these terms here:

• Using CINAHL/MeSH Headings

In other databases, look for a link with the terms "headings", "subject headings", or "thesaurus" to find the appropriate thesaurus terms for your search.

Citation Searching

Citation searching is a search strategy that allows you to search either forward or backwards time through the literature based on an identified relevant article:

You can search forward in time by using databases that allow you to search for other articles that have cited the identified relevant article. (Web of Science and Google Scholar can do this automatically.)

• Web of Science (Clarivate Analytics)
• Google Scholar

You can search backward in time by reviewing the reference list of the identified relevant article for additional article citations.

For more information about how to perform citation searches, check out this guide from the University of Toledo Libraries:

• How To: Cited Reference Searches in Web of Science Guide from the University of Toledo

Retrieving Materials

Select a database.

When searching for articles, it is best to use an appropriate subject database rather than the SearchIT catalog. Be sure to select your database from the Spokane Academic Library homepage to ensure that you will have access to full-text articles.

"Find It @ WSU" Button in PubMed

When you have found an article that you would like to read in its entirety, look for the "Find It @ WSU" Button. This button will take you to the article entry in the SearchIT catalog.

Here's what that looks like in PubMed.

"Find It @ WSU" Button in CINAHL

"Find It @ WSU" Button in PsycINFO

Accessing the Full-Text Article

After selecting the "Find It @ WSU" Button, you will be taken to the article entry in SearchIT. Select the link under the Access Options box to be directed to the full-text article. 

If an article is not available in the WSU Libraries collection, you can request the article through interlibrary loan by selecting the link under "Access Options".

See the Using Interlibrary Loan section for more information.

• << Previous: Developing a Question
• Next: Identifying Peer-Reviewed Resources >>
• Last Updated: Apr 16, 2024 3:40 PM
• URL: https://libguides.libraries.wsu.edu/litreview

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How to do a Literature Review

• Steps in a Literature Review
• Basic Search Functions
• What are subject headings?
• Choosing a Database
• Boolean Operators
• Proximity Operators
• How to document your search
• What is citation harvesting (or citation chasing)

AND is for combining different concepts and will decrease your results

OR is for searching similar concepts and will increase your results

NOT is for excluding specific concepts.   Be VERY careful when using NOT because you may exclude relevant results. NOT will decrease your results.

• << Previous: Choosing a Database
• Next: Proximity Operators >>
• Last Updated: Feb 12, 2024 9:29 AM
• URL: https://libguides.slu.edu/litreview

Conducting a Literature Review

• Literature Review
• Developing a Topic
• Planning Your Literature Review

Developing a Search Strategy

• Managing Citations
• Critical Appraisal Tools
• Writing a Literature Review

A search strategy is an organized structure of key terms used to search a database. The search strategy combines the key concepts of your search question in order to retrieve accurate results.

Your search strategy will account for all:

• possible search terms
• keywords and phrases
• truncated and wildcard variations of search terms
• subject headings (where applicable)

Each database works differently so you need to adapt your search strategy for each database. You may wish to develop a number of separate search strategies if your research covers several different areas. 

It is a good idea to test your strategies and refine them after you have reviewed the search results.

This is a sample planner to develop your search terms from a PICO format

Identifying Search Terms

Once you have developed your research question or chosen your topic you can begin to brainstorm terms to use in your database search.

• Brainstorm terms authors or indexers might use to describe your topic
• Make a list of terminology and relevant terms to use in your search
• Include synonyms or similar terms to combine using the Boolean operator OR
• Search for controlled vocabulary in the databases i.e. search PubMed for MeSH terms

Combine the Elements of Your PICO Question with Boolean Operators

Boolean Operators (Using AND, OR NOT):

Boolean logic is a building block of many computer applications and is an important concept in database searching.  Using the correct Boolean operator can make all the difference in a successful search.

AND, OR, NOT

There are three basic Boolean search commands:  AND ,  OR  and  NOT .

• AND  searches find all of the search terms.  For example, searching on dengue  AND  malaria  AND  zika  returns only results that contain all three search terms.  Very limited results.
• OR  searches find one term or the other.  Searching on dengue  OR  malaria  OR  zika returns all items that contain any of the three search terms.  Returns a large number of results.
• NOT  eliminates items that contain the specified term.  Searching on malaria  NOT  zika returns items that are about malaria, but will specifically  NOT  return items that contain the word zika.  This is a way to fine-tune results. Note:  sometimes  AND NOT  is used; serves the same function as  NOT

Using Boolean Search with Exact Phrases:

If you're searching for a phrase rather than just a single word, you can group the words together with quotation marks.  Searching on "dengue fever" will return only items with that exact phrase.  

When to use Parentheses?

Think of your search in concepts, then put those concepts inside parentheses.  Different databases have different rules about combining searches.  To make sure you get the search you want, use parentheses - every database follows those rules.

Run a Preliminary Search

Look at titles and publication dates to decide which articles you want to look at in depth.

• Select an article and begin the skimming and scanning process.
• If the list has too many irrelevant results, consider selecting different keywords and revising your search.
• If the list has too many results, consider setting date limiters or narrowing your results by searching phrases instead of keywords.
• If the list has too few results, consider selecting different keywords

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• Research Skills Blog

Research Basics: Using Boolean Operators to Build a Search

By Carol Hollier on 02-Dec-2020 10:45:00

Boolean operators are the bones of any good literature search. These operators — or connecting words — tell a database how to combine search terms. Researchers use them to configure their searches to find more precise and relevant results. Knowing how to use them correctly makes all the difference between a frustrating and a satisfactory searching experience.

There are three main search-building Boolean Operators— AND , OR , and NOT .

AND is used to indicate that both terms are present in the results, or all terms if you connect more than two terms with AND.

Helpful to know : In some databases (like PubMed) you need to capitalize your Boolean operators, and in others (like Web of Science) you don’t, but it never hurts to capitalize them. So go ahead and do it!

Depending on where you are searching, your AND search can look like this:

All three configurations above are the same search.

Each additional term or concept that you add with AND will make your search more specific and targeted. Be aware that if you add a term with AND that is the “wrong” term, perhaps capturing an idea with a different word than researchers use, you risk missing relevant results.

Helpful to know about AND In some databases, if you don’t type a Boolean operator between words, the database will treat those words as though they have an AND between them. For example, any databases on the Web of Science platform do this. In others, such as any on the EBSCOhost platform, the database will treat the words as though they are either right next to each other (as a phrase) or close to each other. Exactly how close will depend on behind-the-scenes decisions made by your university library.   To check what’s happening in a database, run a search with two words with an AND, and then run it again without the AND. If the number of results is higher with the AND than without it, you’ll know that you need to type AND to avoid having the database treat your terms as a phrase or as adjacent terms. We will go into what this means in our upcoming blog post 'Research Basics: Phrases and Proximity'.   PubMed combines these approaches. It will pick up some words as phrases that it maps to MeSH headings, but words that don’t correspond to those headings will be treated as though they’ve been typed with an AND. See exactly how PubMed has interpreted your search by looking at the search details on the advanced search page.

While AND refines your search, OR broadens it. Use OR to capture concepts that might be represented with two or more different words. It can be a safeguard against missing results because you’ve used the wrong term, or because researchers have used different terms or different spellings in different parts of the world and over time to capture the concept.

In the diagram below, we use three related words that can all cover the same concept. When we connect each word with OR, we are telling the database that we are happy to have results that have fish in them, or results that have seafood in them, or results that have “sea food” in them. Results could also have both fish and seafood in them, or seafood and “sea food” , or “sea food” and fish , or all three terms. As long as one of the terms appears in the record, it will be included in the results list.

You’ll notice that, strictly speaking, fish and seafood aren’t synonyms, but they are related terms and might both be relevant to your search. This is something that you, the searcher, get to decide. Your decisions about what makes sense to connect with OR should be informed by the language that you see researchers using as you start scanning your results. You don’t need to restrict yourself to only two or three terms in an OR string. You could also, in this example, add in OR salmon OR trout OR sardines and on and on.

Depending on where you are searching, your OR search might look like this:

Notice that the string is typed in one search box and is contained within parentheses. It is generally a good idea to keep each concept that is captured by an OR string in one search box. The parentheses tell the database to keep these terms grouped together as a single concept. Some databases will automatically add in the parentheses around what you’ve typed in a single search box, and others won’t—but it never hurts to add them yourself.

Your OR search could also look like this:

NOT is a powerful, potentially dangerous Boolean operator that must be used with caution. The problem with NOT is that it removes results, and when they are gone you can’t see them so you don’t know if they were removed for the reason you thought they would be.

In the diagram below, all the results that will be returned will have the word potato in them unless they also had the word sweet in them.

In general, it’s safer to refine a search using AND rather than NOT, but there are times when NOT can help you check if your search is doing what you hope and think it is doing. For instance, you could run this search below to decide if you really want to keep “sweet potato*” together in a phrase, or if it would be better to connect the words as sweet AND potato* .  

Notice that to execute this search you need to put potato* AND sweet inside parentheses to indicate that that search needs to happen first before the phrase “sweet potato*” is removed. That will let you see all the records that have the words sweet and potato* in them unless the words are together as a phrase.

Combing Boolean operators

In the search above, AND was combined with NOT. For many searches you will want to combine different Boolean operators. Depending on what kind of search interface you are using, you can either build it all in one go, or you might need to do it step by step.

The way that you are most likely to build a search is to gather together a number of words to represent each concept, and then combine each concept to intersect with the others, like this:

Remember that a database will process, or group together, what you’ve put inside brackets first, so be sure to group together what should be together. Otherwise many will read your string left to right, although others will do something harder to deduce. To get a sense of how important the parentheses are, searching fusarium OR hydrophobin* AND gush* OR flow* AND beer* OR ale OR brew* OR malt* in FSTA on the EBSCOhost platform brings back 71,842 results, but searching (fusarium OR hydrophobin*) AND (gush* OR flow*) AND (beer* OR ale OR brew* OR malt) brings back 86, all of which actually do have each of the concepts in them.

Boolean operators can be a bit confusing, but with a bit of practice and care it is easy to become adept at building search strings that return results that are relevant to the research you are pursuing.

For more information about laying the foundation for strong search skills, we will soon be publishing the following blog posts:

Research Basics: Phrases and Proximity

Research Basics: Truncation.

Please check back soon or sign up for the Research Skills blog mailing list to hear when these are live.

You may also be interested in learning the difference between a systematic review and a systematic literature review , or  literature searching best practice .

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Effective Literature Searching: Boolean Operators

• CoCoPop Framework
• PEO Framework
• PFO Framework
• SPICE Framework
• SPIDER Framework

Boolean Operators

• Identifying Keywords & Subject Headings
• Using MeSH to Build a Search
• Filtering & Narrowing
• Saving Your Results
• Finding Full Text
• PubMed Tips & Tricks
• Still Need Help?

Linking your concepts correctly will help you find the most suitable results. Many databases, including PubMed employ "Boolean operators." Boolean operators are words that connect search terms together to broaden or narrow the results retrieved.

The three Boolean operators are AND, OR, and NOT.

• AND narrows your search by limiting your results to items that contain both words connected with AND.
• OR expands your search by including results that contain one word, the other word, or both words.
• NOT narrows your search by limiting your results to items that contain the word you designate before NOT, but not the word after NOT.

Attribution: Cecelia Vetter, CC BY-SA 4.0, via Wikimedia Commons

• << Previous: Building a Search Strategy
• Next: Identifying Keywords & Subject Headings >>
• Last Updated: Dec 29, 2023 2:55 PM
• URL: https://library.aah.org/guides/literaturesearching

University of Tasmania, Australia

Systematic reviews for health: 7. boolean operators.

• Handbooks / Guidelines for Systematic Reviews
• Standards for Reporting
• Registering a Protocol
• Tools for Systematic Review
• Online Tutorials & Courses
• Books and Articles about Systematic Reviews
• Finding Systematic Reviews
• Critical Appraisal
• Library Help
• Bibliographic Databases
• Grey Literature
• Handsearching
• Citation Tracking
• 1. Formulate the Research Question
• 2. Identify the Key Concepts
• 3. Develop Search Terms - Free-Text
• 4. Develop Search Terms - Controlled Vocabulary
• 5. Search Fields
• 6. Phrase Searching, Wildcards and Proximity Operators
• 7. Boolean Operators
• 8. Search Limits
• 9. Pilot Search Strategy & Monitor Its Development
• 10. Final Search Strategy
• 11. Adapt Search Syntax
• Documenting Search Strategies
• Handling Results & Storing Papers

Step 7. Boolean Operators

Once all free-text terms and controlled vocabulary terms have been identified, you can start the proper searching process. It is recommended to search for each identified search term individually, then use the correct Boolean operators to combine the terms. This will help prevent any human errors. It also allows you to see which search terms add value to the search and if a particular search term produces too many irrelevant results.

Boolean Operators Explained

An OR search will find information which includes either search term. All free text and controlled vocabulary terms identified for a concept are to be combined with an OR. This is to broaden the search and to capture all articles on a topic regardless of which term is used in the article.

An AND search will find results with information common to both search terms. Once all relevant information for each concept has been found, the concepts are joined with AND. This is to narrow the search and to only capture articles in which all concepts appear.

A NOT search will exclude words from your search results. This is to narrow your search, telling the database to ignore concepts that may be implied by your search terms. If you are interested in e.g. only finding human studies you may be tempted to type NOT animals . This means that articles that include the word animals are excluded, including studies on animals as well as humans, which potentially are relevant. As a NOT search has the potential to exclude relevant articles, it is not normally recommended for a systematic review. 

NOTE!  All databases support these Boolean operators. The syntax for the NOT operator may vary slightly. For more information visit the  Search  Help menu within the  relevant database  or  see

Example - In General

Combine all terms within a concept with OR. Then, join the searches for each concept with AND .

Example - In Detail

• Medline via Ovid
• Medline via PubMed

This is how you could approach the example in Medline via Ovid :

1. Carry out separate searches for each free-text term and controlled vocabulary term in Concept 1 of Concept Table.

To search for MeSH terms, use Search Tools  section to Map Term . To search for free-text terms, use Search Fields section and tick relevant fields, e.g. Title, Abstract, Keyword Heading Word.

1   Dementia.ab,kf,ti. 2  Alzheimer.ab,kf,ti. 3   "Huntington*".ab,kf,ti. 4  Kluver.ab,kf,ti. 5   Lewy.ab,kf,ti. 6   exp Dementia/

NOTE!  In Ovid you need to tick a box if you want to explode a MeSH term; the default is non-explode. This is different to PubMed.

2. Combine all individual searches for Concept 1 with  OR:

7  1 or 2 or 3 or 4 or 5 or 6

Either type as above, or select searches 1 to 6 and click Combine with OR .

3. Repeat steps 1 and 2 for all other concepts.

4. Combine the OR searches for each concept with  AND .

44   7 and 22 and 31 and 43

Either type as above, or select searches 7, 22, 31 and 43 and click Combine with AND .

See source of example

This is how you could approach the example in Medline via PubMed :

In PubMed Advanced Search, change the drop-down menu to Title/Abstract or MeSH Terms accordingly, then enter each search term and  Add to History (change Search drop-down)

#1  dementia [tiab] #2  alzheimer [tiab] #3   huntington* [tiab] #4  kluver [tiab] #5   lewy [tiab] #6  dementia [mh]

NOTE!   There is no option for non-exploded MeSH term in the drop-down menu. If you want to not explode a MeSH term, keep the drop-down default of All Fields and use this syntax in the search box: Dementia[MeSH:NoExp] or dementia[mh:noexp]

#7  #1 OR #2 OR #3 OR #4 OR #5 OR #6

Either type as above, or use the Add Query / Add with OR   link in the History under Actions  to bring the individual searches back up into the Query Box . This will give you search #7

(((((Dementia [tiab]) OR Alzheimer [tiab]) OR Huntington* [tiab]) OR Kluver [tiab]) OR Lewy [tiab]) OR Dementia [mh]

#49   #7 AND #24 AND #34 AND #48

Either type as above, or use the  Add Query / Add with OR  link in the  History  to bring the individual searches back up into the  Query Box . This will give you search #49 :

(((((((((Dementia [tiab]) OR Alzheimer [tiab]) OR Huntington* [tiab]) OR Kluver [tiab]) OR Lewy [tiab]) OR Dementia [mh])) AND ((((((((((((((((Animal-assisted therapy [tiab]) OR Animal-assisted activit* [tiab]) OR Animal-assisted intervention* [tiab]) OR Animal therapy [tiab]) OR Pet therapy [tiab]) OR Dog therapy [tiab]) OR Dog-assisted therapy [tiab]) OR Canine-assisted therapy [tiab]) OR Aquarium [tiab]) OR Animal Assisted Therapy [mh:noExp]) OR Pets [mh]) OR Dogs [mh]) OR Cats [mh]) OR Birds [mh:noexp]) OR Bonding, Human-Pet [mh]) OR Animals, Domestic [mh:noExp])) AND (((((((((Music therapy [tiab]) OR Music* [tiab]) OR Singing [tiab]) OR Sing [tiab]) OR Auditory stimulat* [tiab]) OR Music [mh]) OR Music Therapy [mh]) OR Acoustic Stimulation [mh]) OR Singing [mh])) AND ((((((((((((Aggression [tiab]) OR Neuropsychiatric [tiab]) OR Apathy inventory [tiab]) OR Cornell scale [tiab]) OR Cohen Mansfield [tiab]) OR BEHAVE-AD [tiab]) OR CERAD-BRSD [tiab]) OR Behavior* [tiab]) OR Behaviour* [tiab]) OR Aggression [mh]) OR Personality inventory [mh]) OR Psychomotor agitation [mh])

Need More Help? Book a consultation with a  Learning and Research Librarian  or contact  [email protected] .

• << Previous: 6. Phrase Searching, Wildcards and Proximity Operators
• Next: 8. Search Limits >>
• Last Updated: Apr 23, 2024 12:49 PM
• URL: https://utas.libguides.com/SystematicReviews

Literature Searching

• Step 1: Defining the search
• Step 2. Choosing the right database
• Step 3: Constructing the search
• Searching techniques: using Boolean
• MeSH and CINAHL Headings
• What are Primary and Secondary Sources of Information
• Step 4: Conducting the search
• Step 5: Accessing the search results
• How to use databases videos
• Advanced Literature Searching: what are the different types of literature reviews?
• Advanced Searching: Systematic Reviews
• Advanced Searching: help with developing your research question
• Advanced Searching: critical appraisal
• Screening and Selecting studies

What is Boolean? How to make your searching easier

A normal keyword search might be ok for quick and general search but you may find too many results to scroll through. Many of the results will be irrelevant too.

When searching it helps to know what you're looking for, what you're not looking for and having the skills to find it. Using Boolean terms can help. Boolean Search uses a combination of keywords  to organise and sift through your searches. 

Using Boolean techniques when searching can:

• Give more accurate and relevant search results
• You can develop a broad or narrow search terms
• Helps you navigate through appropriate research and disregard unrelated research
• You can apply as many Boolean terms in the same search

Use any or a combination of the techniques below to make searching easier for you.

Boolean techniques

• Phrase Searching "....."
• Truncation .....*
• Advanced Boolean: Parenthesis/Nesting (......)
• Advanced Boolean: Proximity NEAR, W3 ...

Using AND between keywords narrows your search results from just a keyword search

Using OR extends your search out which retrieves more results. Works very well with very similar keywords and means you're not missing out on any relevant research.

Use NOT to exclude results that you're interested in and reduce the number of records retrieved.

Phrase searching works really well on all databases. Works well for a phrase that can also work as separate keywords.

Truncation can extend your search out to ensure you're not missing out on any relevant records. Works with words with different endings. Go to last letter of word before ending changes and add * . Here's some examples:

You can use  parentheses/nesting  to build a search with a combination of Boolean Operators by using (...). The search inside the (...) is always done first so this can affect your search results. 

Some databases allow for searching for words within the same sentence or within a defined number of words within one another e.g.

• << Previous: Step 3: Constructing the search
• Next: MeSH and CINAHL Headings >>
• Last Updated: Aug 18, 2023 9:59 AM
• URL: https://libguides.dundee.ac.uk/literaturesearching

How to undertake a literature search: a step-by-step guide

Affiliation.

• 1 Literature Search Specialist, Library and Archive Service, Royal College of Nursing, London.
• PMID: 32279549
• DOI: 10.12968/bjon.2020.29.7.431

Undertaking a literature search can be a daunting prospect. Breaking the exercise down into smaller steps will make the process more manageable. This article suggests 10 steps that will help readers complete this task, from identifying key concepts to choosing databases for the search and saving the results and search strategy. It discusses each of the steps in a little more detail, with examples and suggestions on where to get help. This structured approach will help readers obtain a more focused set of results and, ultimately, save time and effort.

Keywords: Databases; Literature review; Literature search; Reference management software; Research questions; Search strategy.

• Databases, Bibliographic*
• Information Storage and Retrieval / methods*
• Nursing Research
• Review Literature as Topic*

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How to undertake a literature search

Introduction.

Undertaking a literature search can be a daunting prospect. By breaking the exercise down into smaller steps, you can make the process more manageable. The following ten steps will help you complete the task from identifying key concepts to choosing databases for your search and saving your results and search strategy. It discusses each of the steps in a little more detail with examples and suggestions of where to get help.

There are ten steps to undertaking a literature search which we'll take you through below:

🎬 - Indicates a video is available with more information.

Please click on the boxes below to get a bit more detail on each step.

First, write out your title and check that you understand all the terms. Look up the meaning of any you don’t understand. An online dictionary or medical encyclopaedia may help with this.

If your search is for a dissertation, you may need to choose your own research question. In this case, you will need to consider whether there is likely to be enough research on your topic. Alternatively, if your topic is too broad, you could be overwhelmed by the number of references.

One way of checking how much is written on your topic is to use Library Search. Most libraries offer a Library Search or discovery tool. It provides a quick search across all the library’s holdings. You can also limit your search by date or type of document. If you just need a few references to help you write an essay, Library Search may be helpful. It also gives quick access to full text items.

Next, you need to identify your key concepts. One way to do this is to look at your title and identify the most important words. Ignore words that tell you what to do with the information you find eg evaluate, assess, compare, as these are not generally used as search terms. In the example below, key concepts have been highlighted:

Evaluate the effectiveness of a mindfulness intervention on the health-related quality of life of rheumatoid arthritis patients

Another way to do this is to break down your title using the PEO framework:

P = Population    E = Exposure    O = Outcome 

This works well where there is no comparison between two types of treatment or intervention.

In our example:

P = rheumatoid arthritis patients

E = mindfulness

O =  health related quality of life

Other question formats are available such as PICO or SPIDER

Tip: Not all search topics will include every element of PICO – some include fewer items.

Once you have identified the key concepts, it’s important to think of any other terms or phrases that might have a very similar meaning. Including such synonyms will make your search as thorough as possible. For example, if your topic is looking for articles on Staff attitudes , you might also use the terms:

• Staff perceptions 
• Staff opinions
• Stereotyping
• Labelling 

If the database you are using has a list of subject heading s , this may help you to find the most appropriate term for your subject. Some databases provide definitions for terms used in the database and may suggest related terms.

A comprehensive search will usually include both subject headings from databases and terms that you have thought of yourself.

Tip: Often your search term will be a phrase instead of a single word. To carry out phrase searches, use double quotes, for example “problem drinking”.

Once you have chosen your search terms, you need to think about the best databases for your topic. The databases you choose will depend on the search question and the libraries you have access to.

Tip: It’s well worth taking a few minutes to get to know the databases available on the Library webpages and what they cover.

The next step is to combine your search terms in such a way that you only retrieve the more relevant references for your search question. In order to do this you need to build a search strategy . This involves using Boolean operators such as AND , OR and NOT .

AND narrows the results of the search by ensuring that all the search terms are present in the results. 

OR broadens the results of the search by ensuring that any of the search terms are present in the results.

NOT limits the results by rejecting a particular search term. Be careful with NOT because it will exclude any results containing that search term regardless of whether other parts of the article might have been of interest.

OR will broaden your number of results while AND will produce fewer results.

Try using this  Search-plan-worksheet   to break your topic down into concepts. These can then be linked together when you run the search. You can also add synonyms within each concept box. The yellow limits box is a prompt to think about any limits you want to apply when searching. This leads us to Step 6.

Tip: Most databases will allow you to use a truncation sign (*) or wildcard (?) to pick up various different endings to words or alternative spellings.

For example:  alcohol* would pick up alcohol, alcoholic, alcoholism, etc

Sm?th would find Smith and Smyth

The next step is to think about any other restrictions you want to make to your results.

Common limiters found on databases include:

• Peer reviewed articles
• Research articles
• Age group (adult, child, older person)
• Document type

Not all databases allow all of the limiters above.

When writing a dissertation, primary research articles are normally required. Where the database allows you, try limiting to research articles only.

Non-research materials can also be useful as an overview of your topic; for example a literature review can give an analysis of what has already been written on a topic.

The video below includes a demonstration of how limits can be applied using the CINAHL database as an example:

CINAHL - advanced

Once you have identified all your search terms and any limits you want to apply, you are ready to run your search on the databases you have chosen. 

Once you have some search results, you can look through them and start to select those that look relevant to your literature search. It is likely you will reject some because they are not quite what you wanted but there will be others that can be marked for further attention.

The title of an article on its own may not tell you very much; read the abstract quite carefully to see if the article is relevant or not.

Tip: You can show more details for each record by clicking on the article title. On some databases, there may be an abstract for the article which you can open. 

If you find you are either generating more results than you can possibly look at or too few results to write about, be prepared to adjust your search terms and the way they are combined.

If you get too many results you could try: •limiting to just the most recent material •adding another term or concept and linking it using “AND” •limiting to a particular country or geographical area such as UK

If you get too few results, you might try: •expanding your date range •removing any geographical limits you have applied  •removing the least important term or concept

Tip: Be prepared to try other databases and keep searching until you feel confident you have found enough relevant material.

Once you have selected some articles that look relevant for your piece of work, you will need to save them so that your hard work is not wasted.

At the same time, you will want to save your search strategy . This is a record of the terms you searched, how you combined them, any limits you applied and how many results you found.

You will also need to choose a way to save your results. One way is to email the results to yourself and this can be done from all the databases .

Another way is to export your results to reference management software such as Zotero, RefWorks, EndNote or Mendeley. This software allows you to collect, organise and cite research. It is suitable for managing references over a long period of time. 

The RCN Library and Archive Service provides help with using Zotero . 

Tip: Keep a record of all the databases you use as you carry out your search. It is also a good idea to note where you found any references you subsequently use for your dissertation.

The final step is to obtain the full text of the articles identified in your search which you believe may be useful for your assignment. If you are lucky, many of these will be available electronically and you may just be able to follow a link to the full text.

Alternatively you can copy and paste your article title into the Library search box  and if it is available as full text, a hyperlink will be shown which will link you to the document.

If you are studying elsewhere and have access to a university or hospital library, they may subscribe to different journals to the RCN Library so it is worth exploring what they can offer. If your library does not have either an electronic copy or a physical copy, you may need to request the article by interlibrary loan .

Tip: It is also worth using Google or other browsers to check for the article title you require. Sometimes the article has been made freely available on the internet by the authors.

Boolean operators – words (AND, OR and NOT) which can be used to combine search terms in order to widen or limit the search results.

Database – this is an online collection of citations to journal articles which have been indexed to make retrieval easier. Some databases which also provide full text access to the articles.

Limits – these are options within a database which allow search results to be broken down further. Common limits are year(s) of publication, document type and language. MEDLINE and CINAHL allow age limits too.

Search Strategy – the list of search terms and limits used to retrieve relevant articles from a database in order to answer a search question.

Subject headings – terms that have been assigned to describe a concept that may have many alternative keywords. All these alternative keywords or terms are brought together under the umbrella of this single term. Most health-related databases use subject headings.

Additional information

If after following these steps, you still can’t find what you are looking for, remember that there is always help available at your library. The RCN Library and Archives Service offers a range of help materials via our Literature searching and training pages . These include: • Databases guides in electronic and printed formats • Video tutorials on how to search the databases • 1-1 training sessions pre-bookable via the RCN website face to face or via zoom

A reading list is also available on dissertation and essay support which provides suggestions for key resources, books and journal articles which may help. Click on the link below to access this list:

Dissertation and essay support reading list

Here are other resources you may also find helpful. You will find links to each resource below too:

• Aveyard H (2019) Doing a literature review in health and social care: a practical guide . 4th edn. London: Open University Press.
• Bettany-Satlikov J (2016) How to do a systematic literature review in nursing: a step-by-step guide . 2nd edn. Maidenhead: Open University Press.
• Coughlan M and Cronin P (2016) Doing a literature review in nursing, health and social care . 2nd edn. Los Angeles: Sage.
• De Brún C, Pearce-Smith N, Heneghan C, Perera R and Badenoch D (2014) Searching skills toolkit: finding the evidence . 2nd edn. Chichester: Wiley Blackwell / BMJ Books.
• Hewitt-Taylor J (2017) The essential guide to doing a health and social care literature review . London: Routledge. 

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Conducting a winning literature search

Erika d. ecker.

1 Spectrum Research, Inc., Tacoma, Washington, USA

Andrea C. Skelly

So what is a “winning literature search”? Simply put, it is one that provides you with the information you need to find the types of articles that will help you with clinical practice or research. Literature searching is a combination of an art and a science. Understanding the basic anatomy and physiology of searching can get you started on finding the information you need.

I. Anatomy of a Literature Search—The Skeleton

A. constructing an appropriate question.

• Asking the right question is the primary key to creating a winning search. Your questions must be answerable. If your question is too broad, your search will yield more information than you can possibly look through.

Similarly, if your study was prognostic rather than therapeutic, a PPO table would be used instead of the PICO table in order to help formulate your question. Thus, the categories would change to Patients, Prognostic factors, and Outcome.

⇛ Using treatment studies as an example, the PICO concept can really help you create an answerable question since, as you will see below, it will help you create a search strategy.

B. Using the appropriate database(s)

Now that you have honed your question, it is time to focus on efficient article retrieval. What type of information is needed and what type of articles do you need? What will you do with the information you gather? This will determine the type of information you need and types of articles that may provide that information. It also may influence the type of database you search for that information.

• Bibliographic databases contain references to published literature, such as journals and newspaper articles, conference proceedings and papers, reports, government and legal publications, patents, and books.
• Peer-reviewed literature is scholarly work that generally represents the latest original research in a field. These articles undergo expert screening before publication to ensure meaningfulness within the context of other research in the discipline and, at least in theory, sound methodology.
• “Gray” literature refers to material that is not formally published by commercial publishers or peer-reviewed journals, including reports, fact sheets, white papers, conference proceedings, and other documents from various organizations and government agencies.

The table below provides brief descriptions of common databases and sources to search both peer-reviewed and gray literature.

For example, continuing with our question regarding complications after ADR versus fusion, which type of database listed in the table makes the most sense to search? Indexed peer-reviewed articles will give us the best available and most current data and MEDLINE, which includes millions of citations for biomedical articles and can be accessed using PubMed for free, seems like a great starting place. Generally speaking, PubMed will be the best place to begin your search and there are various ways, as you will see below, to refine and limit your search in order to find exactly what you need.

II. The Physiology of Literature Searching—How It Works

Now that you have an answerable question and an idea of what type of database you need to search (at least to start), let's talk about the nuts and bolts of searching. For the purposes of this paper, we will use PubMed as the search engine.

A. Getting specific—the basics of “how to”

1. Quickstart:

• Type a word or phrase into the query box, including subject, author, and/or journal
• Click on the search button or press the “enter” key

• To retrieve more information about the search results, use the display settings menu (upper left corner) to view the abstract or MEDLINE formats, change the number of items that appear per page, and sort by recently added, publication date, first author, last author, journal, or title.
• PubMed also contains links to full-text articles (appears in upper right corner of page) at participation publishers' web sites as well as links to other third party sites such as libraries and sequencing centers.

⇛ Anything which appears in blue and is underlined is a link that reveals more information. Clicking on the title would bring up the abstract (Abstract format). Clicking on “Related articles” would provide a link to other similar articles that might be of interest.

2. Advanced searching in PubMed—MeSH terms and the MeSH database:

a. Medical subject headings (MeSH)

It is important to understand that PubMed uses a controlled vocabulary to index journal articles called MeSH and uses “automatic term mapping” to find MeSH terms when you search. MeSH terms are organized in a hierarchy called a tree, with more specific (narrower) terms arranged beneath broader terms. By default, PubMed includes in the search all narrower terms; this is called “exploding” the MeSH term. Inclusion of MeSH terms enhances and optimizes the search strategy. For example, if you looked up the term “Spine” in the MeSH database you would see ​ see :

Therefore, PubMed would retrieve every article containing any of the terms located under Spine in the hierarchy.

b. MeSH database features

MeSH vocabulary contains over 25,000 descriptors and is updated weekly and reviewed annually. You can only search citations that have been indexed for MEDLINE (92% of the PubMed database) using MeSH terms. Features include:

• Allows you to identify and select appropriate MeSH terms for a search and to see their definitions
• Builds a PubMed search strategy
• Displays MeSH terms in the hierarchy (MeSH tree) allowing you to broaden/narrow a search
• Limits MeSH terms to a major concept/topic heading for a search
• Allows you to broaden your search by choosing not to explode a term
• The list of subheadings includes terms paired at least once with a given heading in MEDLINE.
• Focuses searches using other types of MeSH terms including publication types [pt], substance names [nm] or registry numbers [rn], and pharmaceutical actions [pa]
• MeSH Brower for access to annotations: http://www.nlm.nih.gov/mesh/

To access MeSH from PubMed, click on MeSH Database on the PubMed homepage or click MeSH under “more resources” in “advanced search.”

Once in the MeSH database, if you entered cancer into the search bar and clicked Go (or hit Enter) you would see ​ see :

Clicking on “neoplasms” will bring up the page where you have the option of selecting any of the features listed above to help you refine your search.

Also, clicking “links” adjacent to the MeSH term desired, will give you a drop-down menu which offers several options:

• PubMed: search PubMed with the term
• PubMed—Major topic: search PubMed with the MeSH term, retrieving only citations where the term is a major focus
• Clinical queries: put the MeSH term into the Clinical Queries box where the search may be further refined
• NLM MeSH browser: show the MeSH browser descriptor data for this term including scope note, allowable qualifiers, and the MeSH tree

⇛ The Mesh database homepage includes three brief tutorials on how to search with the MeSH database, combine MeSH terms, and apply subheadings and other features of the MeSH database.

B. Too much information! Refining your search

• Replace general search terms with more specific terms (the MeSH database would be a great resource for this)
• AND between terms returns only records that contain all of the search terms
• OR between terms returns all records that contain any of the search terms
• NOT between search terms returns only records that contain the first term and not the second
• Example: mimic* will find all terms that begin with the letters m-i-m-i-c-; eg, mimic, mimics, mimicking
• Example: behavio?r will find behaviour or behavior
• Use the “limit” option in PubMed to limit citations by age group, language, publication type, date, human studies, etc.
• Use the “advanced search” option to look up a term as it is indexed in PubMed
• Use the MeSH database features

Let's say we are interested in what the best surgical treatment is for osteoporotic spine fractures. Using some of the tips above, the chart below shows how a typical search might go: ​ go:

By combining terms (using Boolean logic), truncating a term, and using the limits option we were able to narrow our search down from 16,023 articles to a more manageable and relevant 54 articles. The “details” tab in the PubMed search window shows the complete search expression (ie, query translation) employed by PubMed, similar to what is represented in the table above. ​ above.

One of the best resources that PubMed provides for users new to the database is the online tutorials. They are brief but informative and because they are interactive you are guided step-by-step through each process. Perhaps consulting the online tutorials and the fact sheets on PubMed would be a next step for you. Give it a try! In fact, here is the link to the PubMed Tutorial homepage created by the National Library of Medicine: http://www.nlm.nih.gov/bsd/disted/pubmedtutorial/ . Also, check-out the PubMed help page which contains a plethora of information regarding all aspects of PubMed: http://www.ncbi.nlm.nih.gov/bookshelf/br.fcgi?book=helppubmed&part=pubmedhelp

III. Closing Thoughts

Remember, literature searching is a combination of an art and a science. It requires practice, intuition, and some trial and error. While there is a basic structure, a set of guidelines and many tools for assisting one with basic searches, there are a variety of nuances and advanced techniques that may be required for more specialized searches. For systematic reviews as an example, extensive searches are required and may take numerous hours, involving many databases (including those for gray literature), and a combination of advanced search strategies in order to be methodologically sound. Use of personnel with specialized expertise in conducting such searches may provide the best results and be the most resource effective.

• UNC Libraries
• HSL Academic Process
• Scoping Reviews
• Step 3: Conduct Literature Searches

Scoping Reviews: Step 3: Conduct Literature Searches

Created by health science librarians.

• Step 1: Complete Pre-Review Tasks
• Step 2: Develop a Protocol

Partner with a librarian

Systematic searching process, choose a few databases, search with controlled vocabulary and keywords, acknowledge outdated or offensive terminology, helpful tip - building your search, use nesting, boolean operators, and field tags, build your search, translate to other databases and other searching methods, document the search.

• Step 4: Manage Citations
• Step 5: Screen Citations
• Step 6: Assess Quality of Included Studies (Optional)
• Step 7: Extract Data from Included Studies
• Step 8: Write the Review

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  Request a systematic or scoping review consultation

Search the FAQs

About step 3: conduct literature searches.

Click an item below to see how it applies to Step 3: Conduct Literature Searches.

For PRISMA, there are specific items you will want to report from your search.  For this step, review the PRISMA-S checklist.

• PRISMA-S for Searching
• Specify all databases, registers, websites, organizations, reference lists, and other sources searched or consulted to identify studies. Specify the date when each source was last searched or consulted. Present the full search strategies for all databases, registers and websites, including any filters and limits used.
• For information on how to document database searches and other search methods on your PRISMA flow diagram, visit our FAQs "How do I document database searches on my PRISMA flow diagram?" and "How do I document a grey literature search for my PRISMA flow diagram?"

For this step of the review, in Covidence you can:

• Document searches in Covidence review settings so all team members can view
• Add keywords from your search to be highlighted in green or red while your team screens articles in your review settings

Librarian's Role

When designing and conducting literature searches, a librarian can advise you on :

• How to create a search strategy with Boolean operators, database-specific syntax, subject headings, and appropriate keywords 
• How to apply previously published systematic review search strategies to your current search
• How to test your search strategy's performance 
• How to translate a search strategy from one database's preferred structure and syntax to another

The goal of a scoping review search is to retrieve all results that are relevant to your topic in order to map (ie, report on the scope), and to identify themes and gaps in the literature. Because scoping review searches can be quite extensive and retrieve large numbers of results, an important aspect is limiting the number of irrelevant results that need to be screened. Librarians are experts trained in literature searching and scoping review methodology. Ask us a question or partner with a librarian to save time and improve the quality of your review. Our comparison chart detailing two tiers of partnership provides more information on how librarians can collaborate with and contribute to scoping review teams.

Search Process

• Use controlled vocabulary, if applicable
• Include synonyms/keyword terms
• Choose databases, websites, and/or registries to search
• Translate to other databases
• Search using other methods (e.g. hand searching)
• Validate and peer review the search

Databases can be multidisciplinary or subject specific. Choose the best databases for your research question. Databases index various journals, so in order to be comprehensive, it is important to search multiple databases when conducting a scoping review. Consider searching databases with more diverse or global coverage (i.e., Global Index Medicus) when appropriate. A list of frequently used databases is provided below. You can access UNC Libraries' full listing of databases on the HSL website (arranged alphabetically or by subject ).

Generally speaking, when literature searching, you are not searching the full-text article. Instead, you are searching certain citation data fields, like title, abstract, keyword, controlled vocabulary terms, and more. When developing a literature search, a good place to start is to identify searchable concepts of the research question, and then expand by adding other terms to describe those concepts. Read below for more information and examples on how to develop a literature search, as well as find tips and tricks for developing more comprehensive searches.

Identify search concepts and terms for each

Start by identifying the main concepts of your research question. If unsure, try using a question framework to help identify the main searchable concepts. PICO is one example of a question framework and is used specifically for clinical questions. If your research question doesn't fit into the PICO model well, view other examples of question frameworks and try another!

View our example in PICO format

Question: for patients 65 years and older, does an influenza vaccine reduce the future risk of pneumonia, controlled vocabulary.

Controlled vocabulary is a set of terminology assigned to citations to describe the content of each reference. Searching with controlled vocabulary can improve the relevancy of search results. Many databases assign controlled vocabulary terms to citations, but their naming schema is often specific to each database. For example, the controlled vocabulary system searchable via PubMed is MeSH, or Medical Subject Headings. More information on searching MeSH can be found on the HSL Pubmed Ten Tips Legacy Guide .

Note: Controlled vocabulary may be outdated, and some databases allow users to submit requests to update terminology.

View Controlled Vocabulary for our example PICO

As mentioned above, databases with controlled vocabulary often use their own unique system. A listing of controlled vocabulary systems by database is shown below.

Keyword Terms

Not all citations are indexed with controlled vocabulary terms, however, so it is important to combine controlled vocabulary searches with keyword, or text word, searches. 

Authors often write about the same topic in varied ways and it is important to add these terms to your search in order to capture most of the literature. For example, consider these elements when developing a list of keyword terms for each concept:

• American versus British spelling
• hyphenated terms
• quality of life
• satisfaction
• vaccination
• influenza vaccination

There are several resources to consider when searching for synonyms. Scan the results of preliminary searches to identify additional terms. Look for synonyms, word variations, and other possibilities in Wikipedia, other encyclopedias or dictionaries, and databases. For example, PubChem lists additional drug names and chemical compounds.

Display Controlled Vocabulary and Keywords for our example PICO

Combining controlled vocabulary and text words in PubMed would look like this:

"Influenza Vaccines"[Mesh] OR "influenza vaccine" OR "influenza vaccines" OR "flu vaccine" OR "flu vaccines" OR "flu shot" OR "flu shots" OR "influenza virus vaccine" OR "influenza virus vaccines"

Social and cultural norms have been rapidly changing around the world. This has led to changes in the vocabulary used, such as when describing people or populations. Library and research terminology changes more slowly, and therefore can be considered outdated, unacceptable, or overly clinical for use in conversation or writing.

For our example with people 65 years and older, APA Style Guidelines recommend that researchers use terms like “older adults” and “older persons” and forgo terms like “senior citizens” and “elderly” that connote stereotypes. While these are current recommendations, researchers will recognize that terms like “elderly” have previously been used in the literature. Therefore, removing these terms from the search strategy may result in missed relevant articles. 

Research teams need to discuss current and outdated terminology and decide which terms to include in the search to be as comprehensive as possible. The research team or a librarian can search for currently preferred terms in glossaries, dictionaries, published guidelines, and governmental or organizational websites. The University of Michigan Library provides suggested wording to use in the methods section when antiquated, non-standard, exclusionary, or potentially offensive terms are included in the search.

Check the methods sections or supplementary materials of published scoping reviews for search strategies to see what terminology they used. This can help inform your search strategy by using MeSH terms or keywords you may not have thought of. However, be aware that search strategies will differ in their comprehensiveness.

You can also run a preliminary search for your topic, sort the results by Relevance or Best Match, and skim through titles and abstracts to identify terminology from relevant articles that you should include in your search strategy.

Nesting is a term that describes organizing search terms inside parentheses. This is important because, just like their function in math, commands inside a set of parentheses occur first. Parentheses let the database know in which order terms should be combined. 

Always combine terms for a single concept inside a parentheses set. For example: 

( "Influenza Vaccines"[Mesh] OR "influenza vaccine" OR "influenza vaccines" OR "flu vaccine" OR "flu vaccines" OR "flu shot" OR "flu shots" OR "influenza virus vaccine" OR "influenza virus vaccines" )

Additionally, you may nest a subset of terms for a concept inside a larger parentheses set, as seen below. Pay careful attention to the number of parenthesis sets and ensure they are matched, meaning for every open parentheses you also have a closed one.

( "Influenza Vaccines"[Mesh] OR "influenza vaccine" OR "influenza vaccines" OR "flu vaccine" OR "flu vaccines" OR "flu shot" OR "flu shots" OR "influenza virus vaccine" OR "influenza virus vaccines" OR   (( flu OR influenza ) AND ( vaccine OR vaccines OR vaccination OR immunization )))

Boolean operators

Boolean operators are used to combine terms in literature searches. Searches are typically organized using the Boolean operators OR or AND. OR is used to combine search terms for the same concept (i.e., influenza vaccine). AND is used to combine different concepts (i.e., influenza vaccine AND older adults AND pneumonia). An example of how Boolean operators can affect search retrieval is shown below. Using AND to combine the three concepts will only retrieve results where all are present. Using OR to combine the concepts will retrieve results that use all separately or together. It is important to note that, generally speaking, when you are performing a literature search you are only searching the title, abstract, keywords and other citation data. You are not searching the full-text of the articles.

The last major element to consider when building systematic literature searches are field tags. Field tags tell the database exactly where to search. For example, you can use a field tag to tell a database to search for a term in just the title, the title and abstract, and more. Just like with controlled vocabulary, field tag commands are different for every database.

If you do not manually apply field tags to your search, most databases will automatically search in a set of citation data points. Databases may also overwrite your search with algorithms if you do not apply field tags. For scoping review searching, best practice is to apply field tags to each term for reproducibility.

For example:

("Influenza Vaccines"[Mesh] OR "influenza vaccine"[tw] OR "influenza vaccines"[tw] OR "flu vaccine"[tw] OR "flu vaccines"[tw] OR "flu shot"[tw] OR "flu shots"[tw] OR "influenza virus vaccine"[tw] OR "influenza virus vaccines"[tw] OR ((flu[tw] OR influenza[tw]) AND (vaccine[tw] OR vaccines[tw] OR vaccination[tw] OR immunization[tw])))

View field tags for several health databases

For more information about how to use a variety of databases, check out our guides on searching.

• Searching PubMed guide (HSL) Guide to searching Medline via the PubMed database
• Searching Embase Guide
• Searching Scopus guide Guide to searching Scopus via scopus.com
• Searching EBSCO Databases guide Guide to searching CINAHL, PsycInfo, Global Health, & other databases via EBSCO

Combining search elements together

Organizational structure of literature searches is very important. Specifically, how terms are grouped (or nested) and combined with Boolean operators will drastically impact search results. These commands tell databases exactly how to combine terms together, and if done incorrectly or inefficiently, search results returned may be too broad or irrelevant.

For example, in PubMed:

(influenza OR flu) AND vaccine is a properly combined search and it produces around 50,000 results.

influenza OR flu AND vaccine is not properly combined.  Databases may read it as everything about influenza OR everything about (flu AND vaccine), which would produce more results than needed.

We recommend one or more of the following:

• put all your synonyms together inside a set of parentheses, then put AND between the closing parenthesis of one set and the opening parenthesis of the next set
• use a separate search box for each set of synonyms
• run each set of synonyms as a separate search, and then combine all your searches
• ask a librarian if your search produces too many or too few results

View the proper way to combine MeSH terms and Keywords for our example PICO

Question: for patients 65 years and older, does an influenza vaccine reduce the future risk of pneumonia , translating search strategies to other databases.

Databases often use their own set of terminology and syntax. When searching multiple databases, you need to adjust the search slightly to retrieve comparable results. Our sections on Controlled Vocabulary and Field Tags have information on how to build searches in different databases.  Resources to help with this process are listed below.

• Polyglot search A tool to translate a PubMed or Ovid search to other databases
• Search Translation Resources (Cornell) A listing of resources for search translation from Cornell University
• Advanced Searching Techniques (King's College London) A collection of advanced searching techniques from King's College London

Other searching methods

Hand searching.

Literature searches can be supplemented by hand searching. One of the most popular ways this is done with scoping reviews is by searching the reference list and citing articles of studies included in the review. Another method is manually browsing key journals in your field to make sure no relevant articles were missed. Other sources that may be considered for hand searching include: clinical trial registries, white papers and other reports, pharmaceutical or other corporate reports, conference proceedings, theses and dissertations, or professional association guidelines.

Searching grey literature

Grey literature typically refers to literature not published in a traditional manner and often not retrievable through large databases and other popular resources. Grey literature should be searched for inclusion in scoping reviews in order to reduce bias and increase thoroughness. There are several databases specific to grey literature that can be searched.

• Open Grey Grey literature for Europe
• OAIster A union catalog of millions of records representing open access resources from collections worldwide
• Grey Matters: a practical tool for searching health-related grey literature (CADTH) From CADTH, the Canadian Agency for Drugs and Technologies in Health, Grey Matters is a practical tool for searching health-related grey literature. The MS Word document covers a grey literature checklist, including national and international health technology assessment (HTA) web sites, drug and device regulatory agencies, clinical trial registries, health economics resources, Canadian health prevalence or incidence databases, and drug formulary web sites.
• Duke Medical Center Library: Searching for Grey Literature A good online compilation of resources by the Duke Medical Center Library.

Scoping review quality is highly dependent on the literature search(es) used to identify studies. To follow best practices for reporting search strategies, as well as increase reproducibility and transparency, document various elements of the literature search for your review. To make this process more clear, a statement and checklist for reporting literature searches has been developed and and can be found below.

• PRISMA Extension for Scoping Reviews (PRISMA-ScR): Checklist and Explanation Tricco AC, Lillie E, Zarin W, O'Brien KK, Colquhoun H, Levac D, Moher D, Peters MDJ, Horsley T, Weeks L, Hempel S, Akl EA, Chang C, McGowan J, Stewart L, Hartling L, Aldcroft A, Wilson MG, Garritty C, Lewin S, Godfrey CM, Macdonald MT, Langlois EV, Soares-Weiser K, Moriarty J, Clifford T, Tunçalp Ö, Straus SE. PRISMA Extension for Scoping Reviews (PRISMA-ScR): Checklist and Explanation. Ann Intern Med. 2018 Oct 2;169(7):467-473. doi: 10.7326/M18-0850. Epub 2018 Sep 4. PMID: 30178033.
• JBI Manual for Evidence Synthesis Chapter 11: Scoping Reviews Peters MDJ, Godfrey C, McInerney P, Munn Z, Tricco AC, Khalil, H. Chapter 11: Scoping Reviews (2020 version). In: Aromataris E, Munn Z (Editors). JBI Manual for Evidence Synthesis, JBI, 2020. Available from https://synthesismanual.jbi.global. https://doi.org/10.46658/JBIMES-20-12

At a minimum, document and report certain elements, such as databases searched, including name (i.e., Scopus) and platform (i.e. Elsevier), websites, registries, and grey literature searched. In addition, this also may include citation searching and reaching out to experts in the field. Search strategies used in each database or source should be documented, along with any filters or limits, and dates searched. If a search has been updated or was built upon previous work, that should be noted as well. It is also helpful to document which search terms have been tested and decisions made for term inclusion or exclusion by the team. Last, any peer review process should be stated as well as the total number of records identified from each source and how deduplication was handled. 

If you have a librarian on your team who is creating and running the searches, they will handle the search documentation.

You can document search strategies in word processing software you are familiar with like Microsoft Word or Excel, or Google Docs or Sheets. A template, and separate example file, is provided below for convenience. 

• Search Strategy Documentation Template
• Search Strategy Documentation Example

*Some databases like PubMed are being continually updated with new technology and algorithms. This means that searches may retrieve different results than when originally run, even with the same filters, date limits, etc.

• << Previous: Step 2: Develop a Protocol
• Next: Step 4: Manage Citations >>
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SYSTEMATIC REVIEW article

Effect of circadian rhythm and menstrual cycle on physical performance in women: a systematic review.

• 1 Department of Physical Activities and Health Sciences, Faculty of Sports Studies, Masaryk University, Brno, Czechia
• 2 Department of Sport Performance and Exercise Testing, Faculty of Sports Studies, Masaryk University, Brno, Czechia

The literature has extensively investigated potential factors influencing women’s performance, including the menstrual cycle and the circadian rhythm. However, review articles exploring the combined influence of both factors remain lacking in the literature. The study aimed to systematically review the literature on the relationship between the circadian rhythm and menstrual cycle on physical performance in women. The review followed the PRISMA guidelines. The search was performed on the Web of Science, PubMed, Scopus, SPORTDiscus, and Google Scholar databases. Of the 1205 records identified, four articles met the inclusion criteria. From four articles, two studies found a significant interaction between the time of day and phase of the menstrual cycle with physical performance. The isometric strength increased in the afternoon in the mid-luteal phase ( versus the morning in the mid-luteal phase, p < 0.05), and the maximum cycling power was higher in the afternoon in the mid-follicular phase ( versus the morning in the mid-follicular phase, p < 0.01). Our findings suggest that the time of day and the menstrual cycle phase affect physical performance, with the daytime potentially having a more significant influence. However, the results should be interpreted cautiously due to the limited studies and diverse methodologies used to monitor the menstrual cycle phase. This review reinforces the need for further investigation to understand better the combined effects of the circadian rhythm and menstrual cycle on women’s physical performance.

Systematic Review Registration: https://www.crd.york.ac.uk/prospero/display_record.php?RecordID=380965 , identifier CRD42022380965.

1 Introduction

Physical performance (PP) is a complex interplay of multifaceted factors, including the physiological parameters, neuromuscular function, energy expenditure, and psychological elements required to execute a motor task ( Astrand, 1968 ). These tasks involve different components, such as strength, endurance, and power. The investigation into factors influencing PP, particularly within physical activity and sports settings, has been extensive, focusing on understanding the nuances within the female population. Women’s PP has been related to their circadian rhythms (CR), which, in turn, interact with their menstrual cycle (MC), resulting in a complex physiological context that can impact some aspects of physical capabilities. The CR, lasting approximately 24 h, governs diverse bodily processes, including hormone secretion, sleep-wake patterns, basal body temperature regulation, and cognitive and PP ( Postolache et al., 2020 ). Each phase of the CR signifies peaks or falls in different physiological and behavioral functions, significantly influencing factors such as reaction times, physical strength, and endurance ( Youngstedt, Elliott, and Kripke, 2019 ).

Regulated by a central pacemaker in the suprachiasmatic nuclei and influenced by external cues like light, CRs synchronize biological processes with environmental cycles, including daily activities such as exercise ( Mirizio et al., 2020 ; Ayala et al., 2021 ). Individual variations in CRs, known as chronotypes, dictate when the PP peak occurs. For instance, individuals with evening chronotypes may excel in late-day activities due to their natural alignment with circadian peaks. At the same time, those with morning tendencies may perform best in the early afternoon. Additionally, some individuals do not fall into extreme chronotypes and exhibit intermediate preferences, effectively standing apart from these two distinct chronotype categories. These individuals are categorized under ‘neither’ or ‘intermediate’ chronotypes ( Adan et al., 2012 ). Studies indicate that maximal PP typically occurs in the afternoon, coinciding with peaks in body temperature, cardiovascular functions, and metabolic activities ( Hammouda et al., 2013 ; Aloui et al., 2017 ; Bellastella et al., 2019 ). However, this pattern can differ in women due to the physiological changes during the MC.

The MC spans 21–35 days and adds another layer of complexity to the relationship between CRs and PP. Governed by hormonal fluctuations orchestrated by the hypothalamus-pituitary-ovarian axis, the MC consists of distinct phases, each characterized by a specific hormonal environment ( Cook, Kilduff, and Crewther, 2018 ; Paludo et al., 2022 ). The MC is divided into two main phases by ovulation: the follicular and the luteal phases. The follicular phase lasts 7–21 days and begins with the early follicular phase (EFP), characterized by low sex hormone concentrations. EFP aligns roughly with menstruation or menstrual bleeding, part of the uterine cycle ( Hawkins and Matzuk, 2008 ). It is further subdivided into the mid-follicular phase (MFP), with increasing estrogen concentrations, and the late follicular phase (LFP), where estrogen concentrations peak. Following this, the ovulatory phase occurs, marked by a short duration where estrogen concentrations fall after the luteinizing hormone (LH) peak and ovulation. The luteal phase, lasting approximately 14 days, includes the early luteal phase (ELP) with increasing progesterone concentrations, the mid-luteal phase (MLP) with peak progesterone, and the second, smaller peak in estrogen concentrations and late luteal phase (LLP) with decreasing concentrations of both ovarian hormones ( Elliott-Sale et al., 2021 ). These hormonal changes affect some aspects of a woman’s physiology, including sleep patterns, motivation, and perceived PP ( Carmichael et al., 2021 ). Notably, fluctuations in estrogen, progesterone, and testosterone levels throughout the MC can influence strength, power, thermoregulation, and substrate utilization, potentially altering PP capacities ( Smith et al., 2002 ; Carmichael et al., 2021 ).

While research has extensively examined the individual impacts of CRs and the MC on PP, the combined influence remains largely unexplored. Bridging this gap in understanding is crucial for optimizing training and competition strategies for female athletes, considering the intricate interplay between hormonal fluctuations and CRs. By synthesizing existing research and identifying avenues for further investigation, a comprehensive understanding of these intertwined influences can pave the way for tailored training programs and personalized performance optimization strategies in women. Therefore, the purpose of the present systematic review was to summarize the effects of the CR and MC on PP.

2 Materials and methods

A systematic review was performed according to the guidelines of the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) updated in 2020 ( Page et al., 2021 ). The protocol was registered in PROSPERO with the identification number CRD42022380965.

2.1 Eligibility criteria

PECO criteria were used to evaluate the eligibility of the studies. Population = P: (i) eumenorrheic women between 18 and 40 years old; (ii) not taking hormonal contraceptives; (iii) free of any menstrual-related dysfunctions. Exposure = E: (i) at least two daytimes (e.g., 6:00 and 18:00 h); (ii) minimally two different phases of the menstrual cycle (e.g., follicular and luteal phase). Comparator = C: physical performance (example: strength, power, or endurance tests) (i) at different times of the day; (ii) and during the menstrual phases. Outcomes = O: change or maintenance of physical performance in (i) different daytimes; (ii) and menstrual phases.

2.2 Data sources and search strategy

A search strategy was performed in Web of Science, PubMed, Scopus, SPORTDiscus, and Google Scholar databases in December 2022. The search terms with Boolean operators were used in the databases of Web of Science, PubMed, Scopus, and SPORTDiscus (online Supplementary Table S1 ). In Google Scholar, the following terms with Boolean operators were used due to the limited number of characters: (“circadian rhythm” OR “chronotype” OR “diurnal rhythm”) AND (“menstrual cycle” OR “menstruation”) AND (“sport” OR “athletic” OR “athlete” OR “physical activity” OR “exercise” OR “performance”).

An additional data search was performed in January 2024 to ensure the inclusion of the most recent studies. The search followed the same initial criteria, using the same keywords and databases to identify articles published from January 2023 to January 2024. The decision was made to include the latest research findings on the topic.

2.3 Study selection and data extraction

All articles from the databases were imported into Rayyan systematic review software to continue the selection process ( Ouzzani et al., 2016 ). Duplicates, non-English articles, reviews, conference papers, books, and book chapters were excluded by one researcher (MB). Two researchers screened, excluded, or independently accepted the remaining articles (MB, MG). A third person (supervisor, ACP) consulted any disagreement between researchers. The PRISMA flow diagram summarizes the study selection process ( Figure 1 ).

Figure 1 . PRISMA flow diagram of the study selection process.

One researcher (MB) extracted data using Microsoft Excel to organize the study’s primary outcomes. Two tables with information about (i) the sample characteristics and methods and (ii) the measurement of the PP and results were developed.

2.4 Studies methodological quality

The methodological quality of the included studies was conducted independently by two researchers (MB, MG) using the Downs and Black scale ( Downs and Black, 1998 ). This scale consists of a checklist that comprises quality of reporting, internal and external validity, and statistical power ( Downs and Black, 1998 ). A binary score was used for all items, in which 0 = no/unable to determine (UTD); 1 = yes. The original checklist includes 27 questions, nine irrelevant for accepted studies. This modification has been used in previous articles ( Meignié et al., 2021 ; Paludo et al., 2022 ), which had a similar approach (see online Supplementary Table S2 ). Based on these earlier studies, the evaluation of the included studies was converted to percentages and classified as follows: <45.4%, “poor” methodological quality; 45.4%–61.0%, “fair” methodological quality; and >61.0%, “good” methodological quality ( Meignié et al., 2021 ; Paludo et al., 2022 ). A disagreement about the appraisal was resolved by discussion.

3.1 Literature search

A total of 925 articles were found in the researched databases. After the removal of duplicates (n = 306), 619 studies were screened based on title and abstract, in which 124 articles were excluded due to not meeting the criteria established (e.g., review, conference paper, or book), 84 studies were conducted with animals, 28 published in a foreign language, and 374 were not relevant for our review. Two studies were removed because no full text was available, and three articles had an inadequate study design.

One study was found via another search method (accidental find). This study used different search terms for the expression of CR, met the eligibility criteria, and was accepted for our systematic review. Therefore, we again checked databases using this search term (“moment of day”). However, no relevant studies were included. Four studies were included in the systematic review ( Figure 1 ).

The complementary search performed in January 2024 identified 280 new records, and after the removal of duplicates, no additional studies met the eligibility criteria for inclusion in the review. It reaffirms the findings of the initial search of four studies.

3.2 Methodological quality

All studies included were classified using the modified Downs and Black checklist ( Downs and Black, 1998 ) as having “good” methodological quality. Percentage scores for methodological quality were 66.7% ( Birch and Reilly, 2002 ), 68.8% ( Giacomoni and Falgairette, 1999 ; Tounsi et al., 2018 ) to 75.0% ( Bambaeichi et al., 2004 ).

3.3 Outcomes

3.3.1 studies characteristics.

The main characteristics of the four included articles are summarized in Table 1 . The studies presented a sample size ranging from eight participants ( Bambaeichi et al., 2004 ) to 11 ( Giacomoni and Falgairette, 1999 ; Tounsi et al., 2018 ). The studies evaluated high-level soccer players ( Tounsi et al., 2018 ), physical education students ( Giacomoni and Falgairette, 1999 ), moderate physically active females ( Birch and Reilly, 2002 ) and sedentary females ( Bambaeichi et al., 2004 ). The studies used different criteria of selection and the most common were regular MC; non-use of hormonal contraception for at least 4 ( Giacomoni and Falgairette, 1999 ; Bambaeichi et al., 2004 ), 6 ( Tounsi et al., 2018 ) or 12 ( Birch and Reilly, 2002 ) months; free of any sleep disorder ( Bambaeichi et al., 2004 ) or not to be pregnant or breastfeeding within the previous 4 years ( Birch and Reilly, 2002 ).

Table 1 . Sample characteristics, menstrual cycle, and circadian rhythm measurement.

The evaluation of chronotype was limited to a single study ( Bambaeichi et al., 2004 ), despite all articles included in this review assessing PP on at least 2 days occasions (morning and afternoon). Circadian phases were evaluated using rectal temperature ( Giacomoni and Falgairette, 1999 ; Bambaeichi et al., 2004 ) or oral temperature ( Birch and Reilly, 2002 ) as markers.

The participants were observed during at least 2 MC phases (follicular and luteal). The MC phase was established by the day of the MC and confirmed by basal body temperature ( Birch and Reilly, 2002 ; Bambaeichi et al., 2004 ), serum progesterone levels ( Giacomoni and Falgairette, 1999 ; Tounsi et al., 2018 ), moliminal symptoms ( Birch and Reilly, 2002 ) or by urine luteinizing hormone ( Bambaeichi et al., 2004 ).

Different tests were used to assess PP, focusing on strength and endurance performance during the MC and the day, for example, Repeated Shuttle-Sprint Ability Test, Yo-Yo Intermittent Recovery Test, Five Jump Test, or maximal voluntary isometric contraction.

3.3.2 Circadian rhythm and physical performance

Two articles identified a variation in strength and speed endurance performance across the day. In the study by Tousi et al. (2018) , the authors found a significant improvement in strength performance in high-level soccer players, measured by the Five-Jump test, in the afternoon compared to the morning ( p = 0.001). Additionally, an improvement in speed endurance performance was observed in the repeated shuttle-sprint ability test performance in the afternoon compared to the morning ( p = 0.001). Likewise, in the Bambaeichi et al. (2004) study, maximal voluntary isometric contraction of knee extensors under electrical stimulation was significantly increased in the afternoon by 2.6% compared to the morning in sedentary females ( p < 0.05).

3.3.3 Menstrual cycle and physical performance

The relationship between the MC phase and strength performance was identified in one single study ( Bambaeichi et al., 2004 ). Isokinetic peak torque of knee extensors at 3.15 rad s -1 was significantly higher at ovulation than in EFP (76.8 ± 5.7 vs. 73.2 ± 5 N m) in sedentary females and also higher in the MLP (76.9 ± 5 N m) than both EFP (73.2 ± 5 N m) and MFP (72.1 ± 5 N m). To isokinetic peak torque of knee flexors at 1.05 rad s -1 the performance was better during the ovulation (75.5 ± 5 N m) compared to the MFP (68.6 ± 4.2 N m) and MLP (68.4 ± 4.6 N m). The ovulation phase seems the most favorable for isometric contraction of knee flexors. During ovulation, strength performance was significantly better than in the MFP and MLP (75.5 ± 5 versus 68.6 ± 4.2 and 68.4 ± 4.6 N m).

3.3.4 Circadian rhythm, menstrual cycle, and physical performance

The effects of the interaction of the time of day and MC phase were found in two studies. The maximal isometric lifting strength (MILS) differed significantly during the day and MCs, with a considerable increase in performance in the afternoon during the MLP compared to morning in the MLP in moderate physically active females ( p < 0.05) ( Birch and Reilly, 2002 ). On the other hand, the maximal cycling power performance was significantly higher in the afternoon during the MFP compared to morning during the MFP in physical education students (9:00 vs. 14:00 h, p < 0.05; 9:00 vs. 18:00 h, p < 0.01) ( Giacomoni and Falgairette, 1999 ).

The remaining parameters, such as anaerobic endurance, mentioned in Table 2 , were not significantly influenced by the time of day or MC phase ( Birch and Reilly, 2002 ; Tounsi et al., 2018 ).

Table 2 . Main outcomes.

4 Discussion

This systematic review aimed to examine the effect of the interaction between CR and the MC on PP. Initially, the review provided an overview of the potential relationship between CR, MC, and PP. The findings suggest that strength and endurance performance in women may vary depending on the time of day and MC phase. Studies have described increased strength and speed endurance performance during the afternoon. Furthermore, ovulation seems to be the most favorable phase for strength performance, with improvements in isokinetic peak torque and isometric contraction of knee flexors. However, it is worth emphasizing that this finding regarding the ovulation’s optimal phase for performance enhancement is based on findings from a single study, warranting further research for confirmation.

4.1 Circadian rhythm and physical performance

A few studies have already focused on the effect of CR on PP; however, most of them have investigated the male population. Ayala et al. (2021) summarized the possible impact of CR on PP in a systematic review, in which only two out of 36 included studies investigated females, and eight investigated both males and females. In the remaining 26 studies, only men or individuals of undefined sex were examined. Similarly, the gender gap was found by Mirizio et al. (2020) when the authors invested the effect of day on short-duration maximal exercise performance. The author demonstrated that from 66 included articles, two studies included exclusively females and ten studies of both sexes. The remaining samples were made up solely of males, and sex was not mentioned.

Based on previous studies, PP seems to peak during the afternoon, together with the body’s basal temperature ( Mirizio et al., 2020 ; Ayala et al., 2021 ). Additionally, the individual’s chronotype plays a vital role in this phenomenon. Morning chronotypes typically experience their performance peak in the early afternoon, while evening chronotypes experience it later in the afternoon ( Ayala et al., 2021 ). This difference is likely attributed to differences in body temperature patterns, with morning chronotypes exhibiting an earlier peak in the afternoon than evening chronotypes ( Lack et al., 2009 ). Despite the relevance of the chronotype in understanding performance patterns, our systematic review found limited data, with only one included study assessing chronotype without directly correlating it with PP ( Bambaeichi et al., 2004 ).

In general, based on previous literature and the included studies, the PP usually peaks in the afternoon ( Giacomoni and Falgairette, 1999 ; Birch and Reilly, 2002 ; Bambaeichi et al., 2004 ; Tounsi et al., 2018 ; Mirizio et al., 2020 ; Ayala et al., 2021 ). More specifically, Ayala et al. (2021) observed a peak of PP between 16:30–18:30. Mirizio et al. (2020) found a PP peak between 16:00–20:00 and studies included in our systematic review have achieved similar results, with the highest PP at 17:30 ( Tounsi et al., 2018 ) or 18:00 ( Giacomoni and Falgairette, 1999 ; Birch and Reilly, 2002 ; Bambaeichi et al., 2004 ).

On the other hand, the drop in performance occurred in the morning ( Giacomoni and Falgairette, 1999 ; Birch and Reilly, 2002 ; Bambaeichi et al., 2004 ; Tounsi et al., 2018 ; Mirizio et al., 2020 ; Ayala et al., 2021 ). The decrease in performance can be attenuated by using some techniques. For example, Mirizio et al. (2020) recommend an active warm-up protocol or warm-up while listening to neutral or high-tempo music, exposure to warm and humid climate conditions, regular training in the morning for at least 4 weeks, or intermittent fasting conditions.

There is also speculation that peak performance, especially during testing, tends to occur when the training and testing times align ( Bruggisser et al., 2023 ). Therefore, it is prudent to determine the typical training times of the participants who take part in the studies to avoid bias in the performance outcomes.

4.2 Menstrual cycle and physical performance

There is growing attention on the influence of the MC on exercise response in sportswomen. Since 2020, about five systematic review studies have examined the relationship between MC and different components of PP ( Blagrove et al., 2020 ; McNulty et al., 2020 ; Thompson et al., 2020 ; Meignié et al., 2021 ; Romero-Parra et al., 2021 ). Some of the results of these systematic reviews were summarized in an umbrella review published in 2023 ( Colenso-Semple et al., 2023 ), demonstrating the lack of significant influence of the MC phase on acute strength performance or adaptations to resistance exercise training, underlining the need for more rigorous and methodologically consistent research in this area. However, none of these articles focused on the interaction effect between the MC and CR on PP.

Our systematic review suggests improvement in strength performance during the ovulation phase compared to the luteal and follicular phases, according to a study by Bambaeichi et al. (2004) . The remaining studies did not consider the ovulation phase ( Giacomoni and Falgairette, 1999 ; Birch and Reilly, 2002 ; Tounsi et al., 2018 ), examining the EFP, LFP, and luteal phase ( Tounsi et al., 2018 ), MFP and MLP ( Birch and Reilly, 2002 ) or MFP and MLP ( Giacomoni and Falgairette, 1999 ).

Generally, PP appeared to be relatively stable throughout the MC ( Blagrove et al., 2020 ; McNulty et al., 2020 ; Meignié et al., 2021 ; Colenso-Semple et al., 2023 ) but may be trivially impaired during the EFP ( McNulty et al., 2020 ). This phenomenon can be related to the hormonal characteristic of this phase, particularly with lower estrogen and progesterone concentration levels. Estrogen, known for its anabolic properties and influence on metabolic processes such as glycogen uptake and utilization, is essential in protecting muscles against oxidative stress and damage during physical activity. Additionally, its neuroexcitatory impact, which includes enhancing voluntary muscle activation, suggests that higher estrogen levels in phases other than the EFP could potentially improve muscular and exercise performance. In contrast, the lower estrogen levels during the EFP do not confer these performance benefits ( McNulty et al., 2020 ; Carmichael et al., 2021 ). Besides, EFP is marked by menstrual bleeding, symptoms, discomfort, pain, and decreased vigor ( Paludo et al., 2022 ). However, the overall impact on performance during this phase is considered minor, emphasizing the need for individualized consideration of exercise performance across different phases of the MC. Uncertainty in the results of this study can be due to the poor quality of the included studies, various methodologies, and a small number of participants.

4.3 Circadian rhythm, menstrual cycle, and physical performance

Previous sections of this review have explored the influences of CR and the MC effect on PP. Yet, it is crucial to consider their combined effects. The interplay between these two biological processes holds promise for a more holistic comprehension of the optimal conditions for women’s PP.

Distinctively, the MC exerts its influence primarily via hormonal fluctuations. Certain phases, such as ovulation, may boost strength performance due to hormonal profiles ( Bambaeichi et al., 2004 ). Conversely, the CR predominantly modulates performance through physiological variations across the day, with performance peaks commonly observed during the afternoon ( Mirizio et al., 2020 ; Ayala et al., 2021 ).

The intersection of these cycles suggests potential windows within a female cycle wherein performance could be optimized. For instance, the synchronization of the afternoon (a circadian peak) with specific menstrual phases hints at periods of enhanced performance. Nevertheless, existing literature provides scarce direct evidence regarding this intersection. Studies exploring these connections, such as those by Birch and Reilly (2002) and Giacomoni and Falgairette (1999) , offer preliminary insights rather than definitive conclusions. A significant research gap exists in investigations explicitly focusing on the combined effects of these cycles.

4.4 Limitations of the study

Although this systematic review presents the effect of CR and MC on PP for the first time, there are limitations to bear in mind. The lack of studies investigating the current topic, the small sample size, and the different tests and methodologies to assess menstrual phase, strength, and endurance performance measures evaluated among the studies could be significant limitations to the generalization of the results. Considering the lack of a standard for measuring PP or quantifying MC phases and chronotypes, the study’s findings should be interpreted cautiously.

We recommend that future studies on this topic include larger sample sizes of women with different levels of physical activity and sports disciplines to address these limitations. Standardized methods should be used to investigate the effects of time of day and MC phase on PP. Additionally, studies should address potential confounding factors, such as chronotype, hormonal levels, and other physiological or lifestyle factors, that might influence the relationships between CRs, MC phases, and PP. Understanding the interactions between the time of day, MC phase, and PP can better support the optimization of training and competition strategies for women, considering the complex interactions of their biological rhythms to help them reach their full potential.

5 Conclusion

This systematic review is the first to examine the combined effect of circadian rhythm and menstrual cycle on physical performance in women. In summary, the interaction effect of the time of day and phase of the menstrual cycle on physical performance was found in only two studies. While the isometric strength increased in the afternoon in the mid-luteal phase, the maximum cycling power was higher in the afternoon in the mid-follicular phase. These observations are drawn from a minimal number of studies. Our findings suggest that the time of day and the menstrual cycle influence physical performance, with the former potentially having a more significant impact when considered separately. However, interpreting this conclusion warrants caution due to the limited number of studies examining the effect of these factors on physical performance and the variation in methods for tracking menstrual cycle phases. Further research is needed to investigate and clarify the interaction effect of circadian rhythm and menstrual cycle on physical performance.

Data availability statement

The original contributions presented in the study are included in the article/ Supplementary Material , further inquiries can be directed to the corresponding author.

Author contributions

MB: Conceptualization, Data curation, Formal Analysis, Investigation, Methodology, Project administration, Validation, Visualization, Writing–original draft, Writing–review and editing. MG: Conceptualization, Methodology, Validation, Visualization, Writing–review and editing. AP: Supervision, Writing–review and editing.

The author(s) declare financial support was received for the research, authorship, and/or publication of this article. This project was supported by the Specific University Research Grant provided by the Ministry of Education, Youth and Sports of the Czech Republic (number MUNI/A/1455/2022).

Conflict of interest

The authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest.

Publisher’s note

All claims expressed in this article are solely those of the authors and do not necessarily represent those of their affiliated organizations, or those of the publisher, the editors and the reviewers. Any product that may be evaluated in this article, or claim that may be made by its manufacturer, is not guaranteed or endorsed by the publisher.

Supplementary material

The Supplementary Material for this article can be found online at: https://www.frontiersin.org/articles/10.3389/fphys.2024.1347036/full#supplementary-material

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Keywords: biological rhythm, daytime, ovarian cycle, endurance, strength, female

Citation: Beníčková M, Gimunová M and Paludo AC (2024) Effect of circadian rhythm and menstrual cycle on physical performance in women: a systematic review. Front. Physiol. 15:1347036. doi: 10.3389/fphys.2024.1347036

Received: 30 November 2023; Accepted: 20 March 2024; Published: 24 April 2024.

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*Correspondence: Michaela Beníčková, [email protected]

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