Studies conducted on physical activity and brain: a bibliometric analysis

Abstract

Purpose: The purpose of the study is to examine physical activity and brain-related studies published in international and peer-reviewed journals using the Bibliometric Analysis Method.

Material and Methods: By applying the visualized Bibliometric Analysis Method in the study, it was aimed to examine the general distribution characteristics, study progress, and highlights of existing studies on the effects of physical activity on the brain from 2001 to 2022. Studies that were published in journals containing SSCI, SCI-Expanded and AHCI indices of Web of Science (WoS) were examined within the scope of the study. After the elimination criteria were applied, a total of 6007 studies were included in the Bibliometric Analysis.

Results: When the year distributions of the publications were examined, it was found that they were few in number from 1990 to 2000, increased as of 2001, and a significant increase was detected especially in 2019. According to the articles reviewed based on WoS citations, it was found that the fields of neuroscience, clinical neurology and psychiatry came to the forefront. Considering the journal distribution of the examined articles, the PLoS One journal was in the first place. Four main clusters emerged in the common word analysis, which were green, red, blue and yellow. It was obtained that the green cluster occupying the center of the map was the field of sports sciences. The words found in the clusters that emerged from the analysis were physical activity, exercise, cognition, aging, Alzheimer’s disease, depression,dementia, and hippocampus.

Conclusion: The study systematically summarizes and analyzes studies conducted on the promotion of physical activity by emphasizing the improvement of cognitive functions. It is expected that the study will provide guidance and reference for future research.

Introduction

It can be argued that human evolution is shaped by an active lifestyle, and contemporary sedentary behaviors have serious consequences for human health. For this reason, inactivity has become a major public healthcare concern (1). In this context, physical activity level was associated with cardiovascular disease and Type 2 Diabetes (2). It has only recently been understood that physical activity can be a powerful medicine to counter the effects of inactivity. Furthermore, studies report that physical activity has also positive effects on brain structure and health (3-6).

Evidence obtained in human and animal studies reveals that physical activity has direct roles in improving brain health by affecting both brain structure and brain function (7). It is already known that physical activity has important effects on brain health of people of all ages. Regular participation in physical activity during early childhood and adolescence optimize the neuronal environment for cerebral and cognitive development at different stages of life (8). Physical activity may be central to the maintenance of cognitive function by reducing vascular risk factors and preventing a series of neurobiological events that occur as cognitive decline later in life in middle-aged individuals (9,10).

There are also studies conducted on positive effects of physical activity on the preservation of, and even an increase in brain volume (11). Observational studies found that brain volume, particularly in the hippocampus, is preserved in more physically active people (12-14). Physical activity is also associated with the preservation of cortical thickness (15,16). MRImaging displays that white matter integrity is associated with better and higher physical activity levels in individuals, as measured by diffusion tensor imaging (17-19). Also, physical activity is considered to support neuroplasticity, the brain’s ability to continually adapt throughout life, as well as neurogenesis, which is the production of new neurons (20,21).

Although there are numerous publications on physical activity and the brain, few attempts were made to collect bibliometric data systematically to identify research trends and highlight publications that influenced the development of the field. The bibliometric method generally aims to reveal citation paths in the scientific literature or academic publications (22). This method was used in different fields from past to present. However, its use in physical activity and brain studies is limited by a small number of studies conducted in recent years (23-25).

Previous studies focused on all articles on physical activity and the brain published in journals within the scope of Social Science Citation Index (SSCI), Science Citation Index (SCI)-Expanded, Arts & Humanities Citation Index (AHCI), by using the Web of Science (WoS) database. However, common word analysis, which is among the most popular bibliometric methods, was not included in the studies that were conducted based on a descriptive perspective, and limited to trend and co-authorship analyses. Also, most of the bibliometric studies that focused on physical activity and brain research did not use current science mapping methods.

In this context, the present study aimed to analyze the general status of physical activity and brain-related research published in SSCI, SCI-Expanded and AHCI indexed journals in the Web of Science (WoS) Core Collection, and included in international indices from 2001 to 2021 with the help of visual maps, and to contribute to the literature. The study questions that guided the study are as follows.

1. What is the annual distribution of publications on physical activity and the brain?

2. What is the journal distribution of publications on physical activity and the brain?

3. What are the Web of Science (WoS) categories of publications scanned with the keyword “physical activity and brain”?

4. What common word network model emerged from publications on physical activity and the brain?

Material and Methods

Study Model

The model of the study is a case study design, which is one of the qualitative research methods. A case study provides an in-depth examination of a phenomenon or event (26). The case study design was chosen in the study to examine the articles published within the scope of physical activity and brain in terms of bibliometric parameters, and determine the current situation. This research did not require an ethics committee approval.

Search Strategy

The data of this study were obtained from Social Science Citation Index (SSCI), Science Citation Index (SCI)-Expanded, and Arts & Humanities Citation Index (AHCI); and from the articles published between years 2001-2021. The search strategy was to review only articles of peer-reviewed journals in “Physical activity AND Brain” (All Fields), AND 2022 (Excluding Publication Year), AND articles (document type), AND Science Citation Index Expanded (SCI-Expanded), OR Social Sciences Citation Index (SSCI), OR Arts & Humanities Citation Index (A&HCI) (Web of Science Index).

Data Collection Process

The bibliometric data in this study were taken from the Web of Science (WoS) database produced by Clarivate Analytics. The WoS Database is one of the world’s most important scientific citation search and analytical information platforms, and includes many bibliometric indicators and a large database of different disciplines (27).

An online search was made in the WoS Database with bibliometric analysis. The scanning range covered the period between 2001 and 2021. The keywords “physical activity and brain” were scanned in this search both in the article titles and in the article contents, and 6007 records related to the subject were accessed out of a total of 8623 records.

Data Analysis

The Bibliometric Analysis Method was used in the study. Data obtained with the method were compared by two different researchers, the deviating data were reviewed again, and the final results were obtained. Data are presented here in the form of tables and figures. The VOSviewer (Version 1.6.9) package program, which can be used free of charge, was used in the study to make the bibliometric analysis, create maps, and view the articles published on physical activity and brain (28).

Results

Annual distribution of publications on physical activity and the brain

When the trend of the related publications was examined, it was found that they were few in number from 1990 to 2000, increased by gaining momentum as of 2001, and there was a significant increase especially in 2019 (Figure 1).

Figure 1. The distribution of related publications according to years

Journal distribution of publications on physical activity and the brain

When the journal distribution of publications was assessed, it was observed that there were over 1000 journals covering the subject area of ‘physical activity and the brain’. Only journals with more than both 50 citations and 50 publications are given (Table 1), led by PLoS One with 170 articles; followed by Behavioral Brain Research, Frontiers in Aging Neuroscience, and Brain Research, and with over 90 articles. Brain Behavior and Immunity, International Journal of Environmental Research, Neuroscience, Journal of Alzheimer’s Disease, Physiology & Behavior, Scientific Reports, Medicine and Science in Sports and Exercise, Frontiers in Psychology, BMJ Open, Frontiers in Human Neuroscience, and Neurobiology of Aging journals listed more than 50 articles. Finally, the Neuroimage journal published 50 articles.

Web of Science (WoS) categories of publications scanned with the keyword ‘physical activity and brain’

When the categories of related publications were reviewed, the first five fields that had the highest number of publications were ‘Neuroscience’ (1824), ‘Clinical Neurology’ (727), ‘Psychiatry’ (552), ‘Geriatrics Gerontology’ (519), and ‘Sport Sciences’ (491) (Figure 2).

Figure 2. The distribution of related publications according to Web of Science categories

Common word network model emerged from publications on physical activity and the brain

When the keywords that were repeated in the publications were examined, it turned out that 9239 different keywords were used. When the cut-off point was determined as ‘to be used at least 20 times’, 162 frequently used keywords were detected (29). When the map that consisted of these frequently used keywords was examined (Figure 3), it was found that there were four main clusters (green, red, blue and yellow) and relatively smaller clusters. It was also found that the words ‘physical activity’, ‘exercise’, ‘cognition’, ‘aging’, ‘Alzheimer’s disease’, ‘depression’, ‘dementia’, and ‘hippocampus’ were used frequently by different disciplines. Thus, it can be argued that these words are the common keywords used by different fields.

Figure 3. The analysis of keywords

When the clusters are examined, it is understood that the green cluster (the large cluster) focuses on sport sciences. In this cluster, concepts such as physical activity, aerobic exercise, walking and physical fitness reveal that this cluster mostly represents studies related to sport sciences and health. When the frequently used concepts are evaluated, it is seen that these studies mainly focus on pain, lateral sclerosis, sleep, falls, disability, adolescence, aging, fitness and exercise. There are studies related to brain health, physical activity, exercise, cognition, aging, Alzheimer’s disease, dementia, and nutrition in the turquoise cluster, which occupies very little space between the green and red clusters.

The red cluster contains the words Alzheimer’s disease, aging, vitamin D, cancer, mild cognitive impairment, brain volume, blood pressure, amyotrophic, and brain structure. It is considered that this cluster focuses on clinical neurology, geriatrics and gerontology in general, and might refer to areas related to brain health (e.g., epidemiology, dementia, women, lifestyle, diabetes, inflammation, nutrition, depression, biomarkers, and risk factors). There are studies on cerebral blood flow related to more general topics such as physical activity, Alzheimer’s disease, obesity, exercise, hippocampus, and cognition in the orange cluster just above this one.

The blue cluster contains the words oxidative stress, nerve protection, cytokines, anxiety, serotonin, brain-derived neurotrophic factor (BDNF), behavior, neurogenesis, neuroplasticity, autonomic nervous system, mouse, hippocampus, brain, plasticity, and learning. It can be argued that this cluster mostly represents the field of neuroscience. The words related to Covid-19, mental health, heart rate variability, pregnancy, and autonomic nervous system are given in the purple cluster just above this cluster.

Finally, the yellow cluster includes words such as aging, cognitive training, cognition, mood, cardiovascular fitness, prefrontal cortex, memory, executive function, aerobic fitness, executive control, EEG, and attention. This cluster generally seems to represent the multidisciplinary field and displays that these concepts are frequently used in other fields as well.

Discussion

The field of physical activity, which recently received increasing attention, can be considered an area that must be studied together with other disciplines. The bibliometric analysis in this article aimed to add value to the existing literature as it provided an overview of the general publication landscape, and informed the scientific community about the publications that had the greatest effect on physical activity and brain research. In this context, the research problems were discussed respectively.

Annual distribution of publications on physical activity and the brain

It was revealed that the number of publications followed a steep upward trend as of 2001 and increased steadily over time, peaking in 2019 when more than 700 scientific studies were published. Most of the studies were conducted in the United States. The rapid growth in the number of publications might also have played an active role in the physical activity and health promotion programs in the United States. As an example, it is possible to mention the ‘Exercise is Medicine’ health promotion program, which was launched jointly in 2007 by the American College of Sports Medicine and the American Medical Association (30). This program aimed to promote health with physical activity and exercise based on the basic idea of spreading the belief that “exercise is beneficial to the human body and proper exercise prescription is necessary” (24).

Müller et al. used bibliometric data to provide an overview of the eHealth and mHealth research area on physical activity, sedentary behavior and diet, and concluded that the number of articles on mHealth increased rapidly over a 17-year period (31). The findings of our study are similar to those of the studies that were conducted by Müller et al. (23) and Wang et al. (24). Unlike our study, Li et al. (25) conducted bibliometric analyzes of research trends on traditional Chinese health exercises to improve cognitive function, and reported a slight decrease in the publication output between 2001-2002, 2009-2010, and 2014-2016.

Journal distribution of publications on physical activity and the brain

Journals that had more than 50 citations and more than 50 publications in a total of 6007 publications in physical activity and brain research were used as the bibliometric data. All highly cited publications had quantitative design, and most were cross-sectional, experimental and meta-analysis studies. PLoS One is the most popular journal for researchers in this field. The leading journals by citation count represented open access and non-open access journals, and the journals following PLoS One were Behavioral Brain Research, Frontiers in Aging Neuroscience, and Brain Research. Also, Medicine and Science in Sports and Exercise, and BMJ Open journals, which accept many publications in the field of sport sciences, were also included in this ranking. Other journals in the ranking were Frontiers in Aging Neuroscience and Frontiers in Human Neuroscience that included bibliometric analysis findings of trend studies related to exercise to improve cognitive functions by Li et al. (25). Journals that publish open access articles take advantage of citations in terms of citation speed and overall citation count (32). However, the extent of this effect appears to be site-specific, which might explain why many non-open access journals that publish articles on physical activity and the brain receive high citations (33).

Web of Science (WoS) categories of publications scanned with the keyword ‘physical activity and brain’

When the most productive and effective articles on physical activity and the brain were examined, it was observed that authors working in the field of neuroscience came to the forefront in terms of productivity. Also, the fact that the most cited articles were in the field of neuroscience coincided with the number of citations and author productivity. The prominence of neuroscience in terms of the number of publications and citations indicates that there is a need for effective cooperation and publication activities in other fields of physical activity. In this context, increasing projects and funding in the fields other than the abovementioned disciplines will help create research collaborations and quality publications in these fields.

Common word network model emerged from physical activity and brain-related publications

When the keyword analysis was examined, it was determined that 9239 different keywords had been used in the studies. When ‘used at least 20 times’ was determined as the cut-off point, 162 frequently used keywords were reached (29). It was observed that the concepts that became evident in the clusters emerging in the analysis were ‘physical activity’, ‘exercise’, ‘cognition’, ‘aging’, ‘Alzheimer’s disease’, ‘depression’, ‘dementia’, and ‘hippocampus’. Dong et al. (34) stated that the most used keywords were ‘paralysis’, ‘rehabilitation’, and ‘recovery’ in their study that was designed to perform a bibliometric analysis of global trends in studies conducted on exercise interventions for stroke. These keywords highlight research over the past 20 years and can help define the limits of research.

Limitations and Recommendations

The study is the first bibliometric analysis to summarize the progress and trends of scientific studies conducted on physical activity and the brain over the past 20 years based on WoS data, and was derived from 6007 articles and enriched with results. As well as analyzing the number of publications, citations and journals, the study also analyzed subject categories, publication years, authors and keywords.

The study covered physical activity and brain research published in SSCI, SCI-Expanded and AHCI indexed journals in WoS. In this context, not including publications from databases such as ERIC and SCOPUS can be considered the limitation of the study. However, the indices used in the study were chosen because of their high international validity. Only the types of articles that were published in English were selected for the study; book chapters, reviews, and studies written in different languages were excluded. It can be suggested for future studies that different systematic review methods can be used together because methods such as content analysis and thematic analysis were not used in this study.

Conclusion

The study represents the first attempt to conduct a bibliometric study in the field of physical activity and brain research. The study accessed 6007 records on the topic from 2001 to 2021, and revealed that the number of articles published each year is increasing. Most journals were in the fields of medicine and sports. It was determined that the PLoS One journal had the most publications and citations. It was also revealed that the publications scanned with the keyword ‘physical activity and brain’ were mostly in the field of neuroscience. Physical activity, exercise, cognition, aging, Alzheimer’s disease, depression, dementia, and hippocampus were the most important keywords. Although the study had certain limitations, it serves as a reference for future research and highlights the undeniable importance of physical activity for brain health.

Cite this article as: Babayoglu S, Kutlu I, Demirhan G. Studies conducted on physical activity and brain: a bibliometric analysis. Turk J Sports Med. 2023; 58(4):193-99; https://doi.org/10.47447/tjsm.0772

This research did not require an ethics committee approval

Concept:SB,IK,GD; Design: SB,IK; Supervision: GD; Materials: SB,IK; Data Collection and/or Processing: SB,IK; Analysis and Interpretation: SB,IK; Literature Review: SB; Writing Manuscript: SB; Critical Reviews: GD,IK

The authors declared no conflicts of interest with respect to authorship and/or publication of the article.

The authors received no financial support for the research and/or publication of this article.

References

1. Who.int [Internet]. WHO 2020 guidelines on physical activity and sedentary behaviour; c2020 [cited 2020 November 25]. Available from: https://www.who.int/.
2. Wei M, Gibbons LW, Kampert JB, Nichaman MZ, Blair SN. Low cardiorespiratory fitness and physical inactivity as predictors of mortality in men with type 2 diabetes. Ann Intern Med. 2000;132(8):605-11.
3. Chaddock L, Voss MW, Kramer AF. Physical activity and fitness effects on cognition and brain health in children and older adults. Kinesiol Rev. 2012;1(1):37-45.
4. Khan NA, Hillman CH. The relation of childhood physical activity and aerobic fitness to brain function and cognition: a review. Pediatr Exerc Sci. 2014;26(2):138-46.
5. Who.int [Internet]. WHO healthy diet; c2020 [cited 2020 April 29]. Available from: https://www.who.int/.
6. Solis-Urra P, Olivares-Arancibia J, Suarez-Cadenas E, Sanchez-Martinez J, Rodríguez-Rodríguez F, Ortega FB, et al. Study protocol and rationale of the “Cogni-action project” a cross-sectional and randomized controlled trial about physical activity, brain health, cognition, and educational achievement in schoolchildren. BMC Pediatr. 2019;19(1):260.
7. Voelcker-Rehage C, Niemann C. Structural and functional brain changes related to different types of physical activity across the life span. Neurosci Biobehav Rev. 2013;37(9 PtB):2268-95.
8. Chaddock-Heyman L, Erickson KI, Holtrop JL, Voss MW, Pontifex MB, Raine LB, et al. Aerobic fitness is associated with greater white matter integrity in children. Front Hum Neurosci. 2014; 8:584.
9. Norton S, Matthews FE, Barnes DE, Yaffe K, Brayne C. Potential for primary prevention of Alzheimer's disease: an analysis of population-based data. Lancet Neurol. 2014;13(8):788-94.
10. Attems J, Jellinger KA. The overlap between vascular disease and Alzheimer’s disease-lessons from pathology. BMC Med. 2014;12:206.
11. Umegaki H, Sakurai T, Arai H. Active life for brain health: a narrative review of the mechanism underlying the protective effects of physical activity on the brain. Front Aging Neurosci. 2021; 13:761674.
12. Erickson KI, Raji CA, Lopez OL, Becker JT, Rosano C, Newman AB, et al. Physical activity predicts gray matter volume in late adulthood: the Cardiovascular Health Study. Neurology. 2010; 75(16):1415-22.
13. Flöel A, Ruscheweyh R, Krüger K, Willemer C, Winter B, Völker K, et al. Physical activity and memory functions: are neurotrophins and cerebral gray matter volume the missing link? Neuroimage. 2010;49(3):2756-63.
14. Maasakkers CM, Thijssen DH, Knight SP, Newman L, O'Connor JD, Scarlett S, et al. Hemodynamic and structural brain measures in high and low sedentary older adults. J Cereb Blood Flow Metab. 2021;41(10):2607-16.
15. Walhovd KB, Storsve AB, Westlye LT, Drevon CA, Fjell AM. Blood markers of fatty acids and vitamin D, cardiovascular measures, body mass index, and physical activity relate to longitudinal cortical thinning in normal aging. Neurobiol Aging.2014;35(5):1055-64.
16. Lee JS, Shin HY, Kim HJ, Jang YK, Jung NY, Lee J, et al. Combined effects of physical exercise and education on age-related cortical thinning in cognitively normal individuals. Sci Rep. 2016;6:24824.
17. Buchman AS, Boyle PA, Yu L, Shah RC, Wilson RS, Bennett DA. Total daily physical activity and the risk of AD and cognitive decline in older adults. Neurology. 2012;78(17):1323-9.
18. Franchetti MK, Bharadwaj PK, Nguyen LA, Van Etten EJ, Klimentidis YC, Hishaw GA, et al. Interaction of age and self-reported physical sports activity on white matter hyperintensity volume in healthy older adults. Front Aging Neurosci. 2020;12:576025.
19. Wolf D, Fischer FU, Riedel D, Knaepen K, Kollmann B, Kocabayoglu M, et al. The impact of age on the association between physical activity and white matter integrity in cognitively healthy older adults. Front Aging Neurosci. 2020;12:579470.
20. LLorens-Martín M, Torres-Alemán I, Trejo JL. Exercise modulates insulin-like growth factor 1-dependent and -independent effects on adult hippocampal neurogenesis and behaviour. Mol Cell Neurosci. 2010;44(2):109-17.
21. Ahlskog JE, Geda YE, Graff-Radford NR, Petersen RC. Physical exercise as a preventive or disease-modifying treatment of dementia and brain aging. Mayo Clin Proc. 2011;86(9):876-84.
22. Börner K, Chen C, Boyack KW. Visualizing knowledge domains. Annu Rev Inform Sci Technol. 2003;37(1):179-255.
23. Müller AM, Ansari P, Ebrahim NA, Khoo S. Physical activity and aging research: a bibliometric analysis. J Aging Phys Act.2016;24(3):476-83.
24. Wang R, Weng LM, Peng MS, Wang XQ. Exercise for low back pain: a bibliometric analysis of global research from 1980 to 2018. J Rehabil Med. 2020; 52(4):jrm00052.
25. Li W, Weng L, Xiang Q, Fan T. Trends in research on traditional Chinese health exercises for improving cognitive function: a bibliometric analysis of the literature from 2001 to 2020. Front Public Health. 2022;9:794836.
26. Yıldırım A, Şimşek H. Sosyal Bilimlerde Nitel Araştırma Yöntemleri. 8. Baskı. Ankara: Seçkin Yayınları; 2008.
27. Li K, Rollins J, Yan E. Web of Science use in published research and review papers 1997-2017: a selective, dynamic, cross-domain, content-based analysis. Scientometrics. 2018;115(1):1-20.
28. Van Eck NJ, Waltman L. Software survey: Vosviewer, a computer program for bibliometric mapping. Scientometrics. 2010; 84(2): 523-38.
29. Gülmez D, Özteke İ, Gümüş S. Overview of educational research from Turkey published in international journals: a bibliometric analysis. Educ Sci. 2021;46:213-39.
30. Sallis RE. Exercise is medicine and physicians need to prescribe it! Br J Sports Med. 2009;43(1):3-4.
31. Müller AM, Maher CA, Vandelanotte C, Hingle M, Middelweerd A, Lopez ML, et al. Physical activity, sedentary behavior, and diet-related eHealth and mHealth research: bibliometric analysis. J Med Internet Res. 2018;20(4):e122.
32. Ottaviani J. The post-embargo open access citation advantage: it exists (probably), it’s modest (usually), and the rich get richer (of course). PLoS One. 2016;11(8):e0159614.
33. Sotudeh H, Ghasempour Z, Yaghtin M. The citation advantage of author-pays model: the case of Springer and Elsevier OA journals. Scientometrics. 2015;104(2):581-608.
34. Dong Y, Weng L, Hu Y, Mao Y, Zhang Y, Lu Z, et al. Exercise for stroke rehabilitation: a bibliometric analysis of global research from 2001 to 2021. Front Aging Neurosci. 2022;14:876954.