Authors' objectives

To examine the impact that either acute or long-term exercise has on cognition.

Searching

The authors searched the electronic databases of PsycLIT, Educational Research in Completion (ERIC), Dissertation Abstracts, and Completed Research in Education using the keywords: 'cognition', 'cognitive performance', 'mental', 'intellect', 'exercise', 'fitness', 'acute', and 'chronic'. The dates of the search are not reported. Language restrictions are not reported.

Study selection

Assessment of study quality

There was no formal quality assessment, however the authors coded for variables which might affect their quality, including study design, publication status, sampling method, method of assigning participants, and number of threats to internal validity.

Data extraction

The authors do not state who, or how many of the authors, performed the data extraction.

Each study was limited to one set of effect sizes from one comparison group. Outliers were identified as effect sizes more than 3 standard deviations (SD) from the mean and these effects were excluded from the data combining. Each effect size was multiplied by a correction factor designed to yield an unbiased estimate of effect size.

Methods of synthesis

Results of the review

One hundred and thirty-four (134) studies were included with 1,260 effect sizes for the statistical analyses. The total number of participants is not reported.

The overall mean effect size for all of the studies was found to be 0.25 (SD = 0.69, p < 0.05) which suggests that exercise improves cognitive functioning by a small positive effect of 0.25 standard deviations and that this improvement is statistically significantly different from zero.

The adjusted overall mean (after exclusion of outliers and after taking only the best comparison group from each included study) was 0.29 (SD = 0.63, p < 0.05) which was statistically significant.

The results showed that the effect sizes were largest when a cross- sectional or correlational method was used (ES = 0.53), next largest for a chronic training programme (ES = 0.33) and smallest for an acute bout of exercise (ES = 0.16).

Examination of the moderator variables indicated that characteristics related to the exercise paradigm, the participants, the cognitive tests, and the quality of the study influence effect size.

Authors' conclusions

This review suggests that both acute exercise and chronic training programmes benefit cognitive performance. However, even the most avid exercise proponent must recognise that the weakness of the design of these studies has resulted in serious limitations about any conclusions regarding the relationship between exercise and cognition, and have also resulted in ambiguity in terms of the nature of the relationship between exercise or fitness and cognition.

CRD commentary

The authors have stated the research question but have not listed any inclusion or exclusion criteria for the review. The literature search is adequate although the dates of the searches are not given and it is not stated whether there were any language restrictions. Hence, it is possible that non-English studies and unpublished relevant studies may have been missed.

The authors have not reported on how the articles were selected or how many reviewers selected the articles and extracted the data. The quality assessment procedure is described but is not rigorous or scored statistically. Individual study details are not given; neither are the number of participants who were included in the review. The studies are statistically combined using effect sizes which may have been inappropriate because of the variety between the studies and the large number of moderator variables and measurement scales in the individual studies.

The authors mention several methodological drawbacks for the included studies. Since there is insufficient data reported from the individual studies, and about the process of performing this review, so the author's conclusions should be viewed with caution.

Implications of the review for practice and research

Practice: The authors do not state any implications for practice.

Research: The authors state that since effect size increased with decreased experimental rigour, further research is needed that emphasises experimental rigour.

Bibliographic details

Etnier J L, Salazar W, Landers D M, Petruzzello S J, Han M, Nowell P. The influence of physical fitness and exercise upon cognitive functioning: a meta-analysis. Journal of Sport and Exercise Psychology 1997; 19(3): 249-277.

Other publications of related interest

1. Hedges LV. Distribution theory for Glass's estimator of effect size and related estimators. Journal of Educational Statistics, 1981;6:107-28.

Indexing Status

Subject indexing assigned by CRD

MeSH

Cognition; Physical Fitness

AccessionNumber

11998008818

Database entry date

30/09/2000

Record Status

This is a critical abstract of a systematic review that meets the criteria for inclusion on DARE. Each critical abstract contains a brief summary of the review methods, results and conclusions followed by a detailed critical assessment on the reliability of the review and the conclusions drawn.