Exercise as it relates to Disease/Relationship between physical fitness, BMI and cognitive function in school children

This is a critique of the study: Castelli, Darla & Hillman, Charles & Buck, Sarah & Erwin, Heather. (2007). Physical fitness and academic achievement in 3rd and 5th grade students. Journal of sport & exercise psychology. 29. 239-52. 10.1123/jsep.29.2.239.

What is the background to this research?
This study examined the relationship between; physical fitness, body mass index (BMI) and academic achievement of a group of third and fifth grade public school children.

Existing research suggests a strong positive correlation between physical fitness and academic achievement in school children. Children who scored lower on IQ tests were also at higher risk of becoming obese. Although, there is some conflicting research. Another study found a significant positive correlation between physical fitness levels and level of mathematics proficiency, but no correlation between physical fitness level and reading percentile scores or grade point average. However, mathematics proficiency is more highly correlated with cognitive variables than language and reading literacy, which seem to be slightly more influenced by motivational and confidence factors, and therefore may be a better indicator of cognitive ability and IQ. Although research has found a strong relationship between physical fitness and cognitive ability, the evidence is inconclusive, and a causal relationship has not yet been identified. This highlights the necessity for further research in this area.

Higher levels of academic achievement are associated with better life outcomes. Higher IQ correlates to improved job performance and increased train-ability, as well as, lower mortality risk.

Where is the research from?
This study was published in the Journal of Sport and Exercise Psychology (volume 29, issue 2), a peer-reviewed academic journal, which publishes research articles and reviews, examining the relationship between psychology, sports performance and exercise. The authors of the research article; Castelli D. M., Hilman C. H., Buck S. M., and Erwin H. E., are with the Department of Kinesiology and Community Health, University of Illinois, Urbana, IL. Castelli is a professor of health behaviour, health education and physical education pedagogy at the University of Texas, with a Ph.D. from the University of South Carolina, and an expertise in the relationship between cognitive function and physical activity. Castelli and Hilman received a grant from the University of Illinois Research board to fund this study.

What kind of research was this?
The research conducted was an observational, case-control study. Students were compared according to levels of academic achievement in mathematics and reading, and various physical fitness parameters, as well as BMI. The authors hypothesized there would be a relationship between the students' physical fitness and their academic achievement, with aerobic fitness predicted to have the largest correlation. The aim of the study was merely to examine the relationship and correlation between physical fitness and academic achievement. A causal relationship cannot be inferred from this study, as there are many other, unaccounted for, variables and underlying factors to consider. A randomized controlled trial could be used to test certain hypotheses of the direct effect of physical activity on cognitive function.

What did the research involve?
A sample of 259 third and fifth grade students, from across four public schools (all within one school district) underwent fitness and academic testing, the results were then examined by the researchers. The four schools were selected from a total of eleven schools within the district. The four schools were selected specifically to represent the entire range of academic performance and socioeconomic status within the district. The mode of fitness testing implemented was the Fitnessgram test, which involves a series of tests, including; PACER (aerobic fitness test), push-ups, sit-ups and the sit and reach test (flexibility test). BMI scores were also calculated and recorded. Academic achievement was assessed utilising ISAT, which measures reading and mathematics proficiency. The individual scores of each of these tests were compared to each other (with correlations calculated), as well as, to the variables; age, sex, poverty index and school. Regression analyses were also used to determine the relationship between academic achievement and the other variables.

Possible limitations to the study include; the type of testing used, the non-random cohort, and other possible confounding variables (such as motivation) not accounted for.

What were the basic results?
A relationship between physical fitness and academic achievement was found. In particular, aerobic fitness had a strong positive correlation, and BMI had a strong negative correlation, with academic achievement. Other variables including; age, sex, socioeconomic status and school characteristics, were accounted for, and physical fitness was found to correlate with academic achievement regardless of these factors. The other fitness variables (push-ups, sit ups, and flexibility) were not significantly correlated with academic outcomes.

The authors highlighted several potential mechanisms that could explain these results, with reference to previous studies. Physiological and psychological mechanisms were proposed, as well as, neurocognitive, and alterations in brain structure, as possible related causes.

All the mechanisms proposed by the authors assume cognitive performance as being influenced by physical fitness, rather than examining the more complex interrelationship between the two variables. For example, cognitive ability and IQ may influence exercise behaviour. There may also be other confounding factors.

What conclusions can we take from this research?
There is a strong correlational relationship between physical fitness and BMI, and cognitive ability in children. Children that are physically fit tend to have better academic outcomes. The exact mechanisms and causes for this relationship have not been explained by current research. It is probable that it is not a simple causal relationship, where one variable has a direct effect on the other, but rather the two are interlinked and may be subject to other confounding variables.

One study found that socioeconomic status had a direct effect on; physical activity levels, physical health and cognitive function, with IQ acting as a potential underlying, or contributing factor. Another article proposed general intelligence and IQ as a fundamental cause of both socioeconomic status and health outcomes.

Practical advice
Given that the exact mechanism responsible for the relationship between physical fitness and cognitive function has yet to be deduced, it cannot be assumed that an increase in physical fitness will improve cognitive ability. However, based on this study, increased aerobic fitness and decreased BMI may facilitate cognitive function. Therefore, implementing a fitness program to increase aerobic fitness could be beneficial. Regular aerobic activity (at least three times a week) would be a good starting point.

Further information/resources
A recent article outlining the current research on the link between cognitive function and physical activity: Hernández-Mendo, A., Reigal, R., López-Walle, J., Serpa, S., Samdal, O., & Morales-Sánchez, V. et al. (2019). Physical Activity, Sports Practice, and Cognitive Functioning: The Current Research Status. Frontiers In Psychology, 10. doi: https://doi.org/10.3389/fpsyg.2019.02658

Another article with an overview of various potential mechanisms effecting cognitive and physical health: Hillman, Charles & Erickson, Kirk & Kramer, Arthur. (2008). Be Smart, Exercise Your Heart: Exercise Effects on Brain and Cognition. Nature reviews. Neuroscience. 9. 58-65. doi: 10.1038/nrn2298. Link:https://www.researchgate.net/publication/5753778_Be_Smart_Exercise_Your_Heart_Exercise_Effects_on_Brain_and_Cognition