Introduction

The idea that physical activity promotes mental acuity, or "mens sana in corpore sano" (a sound mind in a healthy body), is ancient. Over the past decade, the federal government has increased pressure on schools to improve academic achievement through the No Child Left Behind Act of 2001. This pressure has resulted in less time and fewer resources being allocated to physical education^[1,2] during an epidemic of overweight and obesity in children.^[3] Less physical activity also may lead to poorer cognitive development and academic achievement.^[4]

These trends have prompted renewed interest in studies that examine the links between fitness and physical activity and cognition and academic achievement in children. Many cross-sectional studies have documented better cognition and academic achievement in children who are fitter; however, the evidence that physical activity directly benefits children's cognition and achievement remains tentative. To date, only a few randomized trials have tested the effect of physical training on cognition or academic achievement in children. This review focuses on experimental evidence in this area.

Executive Function in Children

To be successful, it is essential to have good executive function, or supervisory control of cognitive processes. Good executive function, which is necessary for planning and carrying out goal-directed behavior, includes goal-setting, use of strategies, self-monitoring, self-control (ie, inhibition), and allocation of attention and memory.^[5]

Executive function develops during childhood and adolescence^[6-9] and is crucial for adaptive behavior and child development.^[10] Working towards goals often requires a child to suppress behaviors that lead to immediate reward in order to increase the possibility of later rewards (ie, delayed gratification).^[11] The capacity to self-regulate behavior is important to a child's readiness for elementary school,^[12] and executive function in early childhood tracks into adolescence. Preschoolers' ability to delay gratification through the use of strategies to divert attention away from temptations has been shown to predict performance on an inhibitory task in adolescence.^[13]

Exercise and Cognition

The executive function hypothesis posits that the benefits of exercise on cognition are specific to, or stronger for, processes that require cognitive control.^[14,15] Some experimental evidence supports the idea that exercise might improve children's cognition. In a study of fourth, fifth, and sixth graders, Tuckman and Hinkle^[16] found that children randomly assigned to a 12-week aerobic running program (30 minutes per session, 3 times a week) performed better than children in a regular physical education class on a test of executive function conceptualized as creativity (cognitive flexibility measured by the Alternate Uses Test^[17]) but not on a test of planning (ie, a maze tracing test^[17]).

The same investigators found similar results in eighth graders. Participants in an aerobic running program performed better on evaluations of creative thinking than did those assigned to regular physical education classes.^[18] These results partially support the hypothesis that executive function is sensitive to the effects of aerobic exercise training in children.

More recent studies by Davis and colleagues^[19,20] and Kamijo and colleagues^[21] provide further evidence that executive function is sensitive to aerobic exercise training. In the first study to explicitly test the executive function hypothesis in children,^[19,20] Davis' team randomly assigned 171 sedentary, overweight or obese 7- to 11-year-olds (56% female, 61% black) to either low-dose aerobic exercise (20 minutes per day), high-dose aerobic exercise (40 minutes per day), or a control group offered no exercise program. Aerobic exercise included running games, jump rope, and modified basketball and soccer, and the emphasis was on enjoyment and intensity rather than on competition or skill enhancement. Exercise conditions of the intervention (5 days per week for about 13 weeks) were equivalent in intensity (average heart rate was 166 beats per minute) and differed only in the volume of daily exercise. Cognitive functioning was assessed by the Cognitive Assessment System, a standardized psychological assessment that measures 4 interrelated cognitive processes: Planning, Attention, Simultaneous processing, and Successive processing. Only the Planning scale measures executive function (ie, strategy generation and application, self-regulation, intentionality, and use of knowledge). The investigators predicted and observed a dose-response benefit of exercise specific to executive function as measured by the Cognitive Assessment System Planning score.

Using functional MRI in a subsample of participants in the same study, brain activity was measured during tasks requiring executive function (inhibition). Neuroimaging data revealed changes in neural activity in the prefrontal cortex circuitry corresponding to the benefit of exercise on executive function observed in the exercise groups. Children assigned to exercise showed increased bilateral prefrontal cortex activity and decreased bilateral posterior parietal cortex activity compared with controls.

This study is distinctive and clinically relevant for several reasons. The Cognitive Assessment System can be used in formal psychoeducational assessment to determine educational placement and therefore is more applicable to the school setting than are laboratory measures of cognition. The size of the study reduces bias and provides more reliable effects than smaller samples. Inclusion of African American boys and girls provides evidence for the benefit of exercise in this population, which is at increased risk for obesity and poor academic outcomes. Consistent effects regardless of age, race, gender, baseline cognitive performance, and socioeconomic status increase confidence in the translation of these findings to a wide range of children. The report adhered to Consolidated Standards of Reporting Trials (CONSORT) criteria for reporting of randomized clinical trials, including intent-to-treat analysis, thus providing solid evidence for clinical decision making.

Kamijo and colleagues^[21] randomly assigned 43 children, aged 7 to 9 years, to either a 9-month after-school physical activity program or a control group. The exercise program was moderate to vigorous in intensity, lasted at least 70 minutes, and focused on age-appropriate exercise games. Working memory, which has been associated with academic performance in mathematics and reading, was assessed during a cognitive task while the cognitive preparation process was assessed through neuroelectric measurements. Kamijo and colleagues found that children in the exercise intervention performed better on both the task of working memory and the measurement of cognitive preparation process compared with controls. Unfortunately, a number of participants were excluded from analyses due to noncompletion of the cognitive task or technical difficulties during neuroelectric measurements, and therefore conclusions must be considered tentative.

Exercise and Academic Achievement

The impact of exercise on children's cognition implies a link to academic performance. Population studies provide evidence that inactivity and excess weight are associated with poor academic achievement. Cross-sectional and longitudinal studies performed in the Americas, Europe, and Australia provide clear evidence for the association of inactivity and obesity with poorer academic performance.^[4,22-30] A recent prospective study showed that girls, but not boys, who spent 1 to 5 hours per week in physical education had greater achievement in mathematics and reading than those who spent 35 minutes or less per week.^[31] These studies do not indicate a causal role, however.^[30]

Achievement has also been related to fitness.^[4,19] Statewide studies have found a positive relationship between FitnessGram® (a fitness assessment and reporting program for youth) scores and performance on academic achievement tests.^[32,33] Overweight and low fitness levels are markers of a sedentary lifestyle; therefore, physical activity may be the active ingredient behind these associations. For example, a cross-sectional study verified the association between overweight and low scores on academic performance tests, but most of these results were attributable to fitness and socioeconomic status.^[34]

Few randomized trials have examined the effect of physical activity on achievement. Until recently, the strongest statement one could make regarding the effect of physical activity on academic achievement is that at least it does not worsen achievement, even when it takes away from classroom time.^[35] Prior to the studies by Davis and colleagues^[20,36] and Donnelly and colleagues,^[37] only 1 randomized study of exercise had found improvements on an objective measure of children's academic achievement.^[38] Although no difference was detected on an intelligence test, children who trained aerobically for 8 months had an advantage over children who did not train aerobically on a standardized academic achievement test.

In contrast, Coe and colleagues^[39] failed to detect an improvement in standardized tests of academic achievement following a semester of vigorous physical activity in sixth-grade students; however, exercise was associated with higher grades. Dwyer and colleagues^[40] also failed to find an effect of physical activity on standardized tests of academic performance after assigning schools to experimental (a 75-minute, daily endurance fitness program) or control (a skill-based or a traditional fitness program) conditions.

Interpreting some studies is difficult due to methodological limitations. The Sports, Play, and Active Recreation for Kids project^[41] showed that, despite spending twice as many minutes per week in physical education programs, children in the more active group performed no better than did children in the less active group. However, this landmark study suffered from high dropout rates and subject selection bias. Another important study, the Three Rivers Project,^[42] used teacher-assigned grades as the primary outcome measure instead of an objective standardized test.

Donnelly and colleagues^[37] showed that regular, brief bouts of classroom physical activity (at least 75 minutes per week over 3 years) that incorporated academic material (eg, hopscotch as a spelling lesson) benefited achievement for reading, math, spelling, and composite scores, as measured by the Wechsler Individual Achievement Test.

The exercise intervention in overweight children conducted by Davis and colleagues,^[20] described earlier, observed beneficial effects of exercise on mathematics achievement. There were no differences, however, in reading achievement between children in the exercise groups and children in the control group. In addition to measuring academic achievement, Davis and colleagues^[36] obtained teacher reports of classroom behavior. Teacher ratings of children's behavior (Conners Rating Scale) improved somewhat in response to exercise, although these results did not reach statistical significance. Children in the exercise groups had lower adjusted posttest scores than did children in the control group on Cognitive Problems/Inattention (P=.07) and Attention Deficit Hyperactivity Disorder scales (P=.09). High scores on the Cognitive Problems/Inattention scale suggest problems with attention, work organization, completion of tasks and schoolwork, and concentration on tasks that require continuous mental effort.

There is some evidence that short bouts of physical activity, such as recess, may improve classroom behavior.^[43-45] Collectively, these experimental studies offer evidence that exercise can improve cognition and suggest effects on school performance and classroom behavior.

Conclusions and Future Directions

In a period when greater emphasis is being placed on preparing children to take standardized tests, these studies should give school administrators reasons to consider investing in quality physical education and vigorous activity programs, even at the expense of time spent in the classroom. Time devoted to physical activity at school does not harm academic performance and may actually improve it.

Small benefits have been detected with 20 minutes per day of vigorous physical activity.^[20] Achieving this level of activity in physical education programs is possible but would require more physical education time and an enhanced curriculum that prioritizes vigorous activity.^[35] Incorporating 40 minutes per day of vigorous activity to attain greater cognitive benefits would require additional programs available to children of all skill levels.^[20]

After-school programs that allow time for both academic enrichment and vigorous physical activity would meet the need of many families for a safe, constructive environment for children while parents are working. Integrating physical activity into classroom instruction has great promise, if adopted by educators at a dose adequate to affect achievement, and offers an alternative or complementary approach to accrue adequate physical activity.

Children with attention-deficit disorders, who have a pathognomonic executive function deficit, may derive particular benefit from physical exercise; however, little evidence exists in this population.^[46] The study by Davis and colleagues^[19] included a sensitivity analysis for the 6% of children enrolled who were on medication for this disorder and found no differential effect.

Finally, although studies have elegantly demonstrated the mechanisms by which exercise affects cognition, neurogenesis, and angiogenesis in animals,^[47] little is known about the mechanisms of benefit in children. Aerobic fitness has failed to explain the benefit of exercise to cognition in humans.^[48] A preliminary report from a randomized trial showed a link between greater activity intensity (time above the target heart rate) and cognitive performance for children in the experimental group; however, no results compared with the control condition have been reported.^[49] Thus, further investigation is needed to confirm and clarify the promise of physical activity to improve children's academic outcomes.

The health benefits of physical activity are well known, however, and the need to avert sequelae of obesity and inactivity is urgent, so the implementation of accessible, low-cost physical activity programs for youth should be pursued without delay.