The experiment tested the effect of approximately 3 months of regular aerobic exercise on executive function in sedentary, overweight children using cognitive assessments, achievement measures, and fMRI. This multifaceted approach revealed convergent evidence that aerobic exercise improved cognitive performance. More specifically, blinded, standardized evaluations showed specific dose response benefits of exercise on executive function and math achievement. Increased prefrontal cortex activity and reduced posterior parietal cortex activity due to the exercise program were observed.
In sum, these results are consistent with those in adults regarding demonstrable behavioral and brain activity changes due to exercise (Colcombe et al., 2004
; Pereira et al., 2007
). They also add evidence of dose response, which is particularly rare in exercise trials with children (Strong et al., 2005
), and provide important information on an educational outcome. The high dose condition resulted in mean Planning scores 3.8 points, or a quarter of a standard deviation (σ = 15), higher than the control condition. Demographics did not contribute to the model. Similar results were obtained when children with attention deficit disorder or 7-year-olds were excluded. Therefore the results may be generalized to overweight Black or White 7- to 11-year-olds.
Executive function develops in childhood, and is crucial for adaptive behavior and development (Best, Miller, & Jones, 2009
; Eslinger, 1996
). In particular, the capacity to regulate one’s behavior (e.g., inhibiting inappropriate responses, delaying gratification) is important for a child to succeed in elementary school (Blair, 2002
; Eigsti et al., 2006
). This effect may have important implications for child development and educational policy. The finding of improved math achievement is remarkable, given that no academic instruction was provided, and suggests that a longer intervention period may result in more benefit. The improvement observed on achievement was specific to mathematics, with no benefit to reading.
We hypothesize that regular vigorous physical activity promotes children’s development via effects on brain systems that underlie cognition and behavior. Animal studies show that aerobic exercise increases growth factors such as brain derived neurotrophic factor, leading to increased capillary blood supply to the cortex and growth of new neurons and synapses, resulting in better learning and performance (Dishman et al., 2006
). Experimental and prospective cohort studies conducted with adults demonstrate that long-term regular physical activity alters human brain function (Colcombe et al., 2004
; Weuve et al., 2004
). A randomized, controlled experiment revealed that 6 months of aerobic exercise led to improved cognitive performance in older adults (Kramer et al., 1999
). An important paper reports clear evidence for the impact of aerobic exercise on brain activity in adults in two studies using fMRI techniques: A cross-sectional comparison of high-fit to low-fit individuals showed that prefrontal cortex activity was related to physical fitness, and an experiment showed that 6 months of aerobic exercise (walking) in sedentary 55- to 77-year-olds increased prefrontal cortex activity and led to improvements on a test of executive function (Colcombe et al., 2004
). Interestingly, a meta-analysis found no support for aerobic fitness as a mediator of the effect of physical activity on human cognition (Etnier, Nowell, Landers, & Sibley, 2006
). Thus, rather than being mediated by cardiovascular benefits, the cognitive changes due to exercise may be a direct result of neural stimulation by movement. While the case has been made that physical activity may affect children’s cognitive function directly via changes in neural integrity, there are other plausible explanations, such as engagement in goal directed, effortful mental involvement (Tomporowski et al., 2008
This study has limitations. The results are limited to a sample of overweight Black and White 7- to 11-year-old children. Lean children and those of other ethnicities or age groups may respond differently. It is unknown whether cognitive benefits persist after a period of detraining. If benefits accumulate over time, however, this would be important for child development. There may be sensitive periods during which motor activity would exert a particularly strong effect on the brain (Knudsen, 2004
). It remains to be determined whether other types of exercise, such as strength training or swimming, are also effective. Participants and intervention staff could not be blinded to experimental condition or the study hypothesis; however, the recruitment materials emphasized physical health benefits rather than cognitive ones. Another limitation is that the use of a no-intervention control condition does not allow the trial to rule out some alternative explanations (e.g., attention from adults, enjoyment). Psychological changes may occur in children who participate in exercise because of social interactions that occur during the sessions rather than due to exercise per se
. The dose response pattern of results belies this explanation, however, because both exercise groups spent equal time at the research facility with instructors and peers.
The study did not find a difference between the exercise dose groups. This does not conflict with the dose response finding, which shows that the exercise intervention caused an improvement in cognition (Hill, 1965
). Given that the linear contrast demonstrated a graded effect of treatment, a pairwise dose comparison asks a follow-up question, whether one specific dose is superior to another (Ruberg, 1995). The test of the dose-response benefit to achievement was significant, but the comparison of the control group to the two exercise groups was not, providing partial support to the hypothesis that exercise improves mathematics achievement.
The fMRI results are limited by a small sample size and do not provide a test of dose response, which renders them more subject to alternative explanations. Nevertheless, specific changes were observed, and the direction of changes differed in prefrontal and parietal regions, arguing against a global trend in brain activity. Although antisaccade performance and its supporting brain activity change with age (Luna et al., 2001
), this is an unlikely confounder because the groups were of similar age.
These experimental data offer evidence that a vigorous after school aerobic exercise program improved executive function in dose response fashion among overweight children; social factors may have contributed to this effect. Changes in corresponding brain activation patterns were observed. These results also provide partial support of a benefit to mathematics performance. The assignment of conditions was randomized and outcome evaluations blinded, minimizing potential bias or confounding. Overweight children now constitute over a third of U.S. children and are overrepresented among disadvantaged populations. Besides its importance for reducing health risks during a childhood obesity epidemic (Ogden et al., 2006
), aerobic activity may prove to be an important method of enhancing aspects of children’s mental functioning that are central to cognitive development (Welsh, Friedman, & Spieker, 2006