Despite frequent reports that regular exercise benefits the adult brain, when it comes to schoolchildren, the concept of the dumb jock persists. The star quarterback stands in stark contrast to the math-team champion. After all, the two types require seemingly disparate talents: physical prowess versus intellect. Letting kids run around or throw a ball seems, at best, tangential to the real work of learning and, at worst, a distraction from it.

Parents, teachers and education policy makers have pitted athletics against academics even as they trumpet exercise as an antidote to obesity and poor health. From preschool onward, teachers encourage children to sit still rather than scamper. Many schools have cut back on physical education to make room for the three R’s. And when student scores on standardized tests become of primary importance to parents, politicians or other stakeholders in the education system, educators may feel pressured to direct students toward academic pursuits and away from athletic ones.

But accumulating evidence strongly suggests that such thinking is wrongheaded. Time spent horsing around outdoors or playing on sports teams can help kids concentrate and improve their performance in the classroom. Recent studies have linked students’ cognitive performance with measures of physical fitness such as aerobic capacity—the ability of the heart, lungs and blood vessels to cope with intense exercise—and body mass index (BMI), a metric that relates body weight to height. What is more, enrolling kids in exercise programs appears to help them excel academically. Investigators are also revealing how exercise expands the mind, by fostering the formation of new connections between brain cells.

From Agility to Ability
In adults, regular aerobic exercise is associated with improved intellectual abilities and, as time goes on, a lower rate of cognitive decline and a diminished risk of dementia [see “Fit Body, Fit Mind?” by Christopher Hertzog, Arthur F. Kramer, Robert S. Wilson and Ulman Lindenberger; Scientific American Mind, July/August 2009]. And developmental psychologists have long suggested that in young children there is a link between physical and mental growth. Early in life, agility leads to ability: by manipulating objects such as light switches and zippers, two- to five-year-olds develop a real-world knowledge base. For example, a child who builds with blocks or uses simple tools gains experience with the basic laws of physics: when the blocks are stacked askew, she learns, her tower crumbles; if he lets go of a hammer, he discovers, it can bruise his foot.

But although the cognitive benefits of manipulating toys and tools are well known, only in the past decade have scientists begun uncovering a link between more vigorous physical activity and intellect in children. In 2008 psychologist Charles H. Hillman of the University of Illinois and his colleagues examined research results on exercise and cognition from studies dating back to the 1990s. Their review included about a dozen investigations of children and teenagers, most of which showed that higher levels of aerobic fitness—but not muscle strength or flexibility—were associated with better performance on standardized tests and in school. In other words, the more physically fit the young person, the more likely he or she is to get good grades—a connection that holds from elementary school all the way through college.

For example, in 2007 a team led by education researcher Darla M. Castelli, also then at Illinois, assessed the physical fitness of 259 third- and fifth-grade students by measuring each child’s BMI and by giving each of them a running exam and a test of muscle strength. The investigators found that a child’s average performance on math and reading tests was directly related to his or her aerobic capacity—that is, the distance they could run.

Bolstering the link between physical and academic fitness, neuroscientist Hans-Georg Kuhn of the University of Gothenburg in Sweden and his colleagues recently discovered a relation between aerobic capacity and IQ in young adults. In a study published in November 2009, the scientists reviewed the scores of more than one million men on the physical-fitness and intelligence tests that they took when they enlisted in the military at age 18. Again the results indicated that cardiovascular fitness, but not muscle strength, was associated with overall intelligence. And after scouring other national databases, the researchers found that being physically fit at age 18 was correlated with a higher level of scholarly achievement in later life.

In May 2010 physiologist Christian Roberts of the University of California, Los Angeles, and his colleagues reported additional support for the idea that aerobic conditioning and academic success go hand in hand. The investigators tested the athletic proficiency of 1,989 fifth, seventh and ninth graders attending California schools by timing how fast they could run (or walk) a mile and measuring their BMIs; the investigators then correlated these fitness measures with the students’ standardized test scores. They found that the students whose run/walk times exceeded California standards—or whose BMIs were above national guidelines—scored lower on math, reading and language tests than did students with higher fitness levels, even among children whose parents had similar educational backgrounds.

Reading, Writing and Rugby
However strong the correlations between physical fitness and academic performance, they do not necessarily mean that exercising leads to cognitive improvement. They might simply indicate that the parents who encourage their kids to exercise are also the ones who push them academically. Having involved parents, rather than being athletic, could explain these children’s academic abilities.

To determine whether exercise has a direct effect on reasoning abilities, researchers conduct so-called intervention studies, in which they add athletics to children’s daily routines and assess the impact on learning, memory and the ability to concentrate. And many such studies reveal that additional athletic conditioning can boost test scores and school performance. In 2008 kinesiologist Phillip D. Tomporowski of the University of Georgia and his colleagues surveyed results from 12 research teams that had enrolled schoolchildren in exercise regimes lasting between 20 days and six months. Tomporowksi’s team concluded that making kids move around more can sharpen intelligence, enhance creativity and planning skills, and improve math and reading performance (based on standard measures of those traits and skills).

In a review of 17 studies (seven of which involved getting kids to exercise more) from 2008, health scientists Franois Trudeau of the University of Quebec and Roy J. Shephard of the University of Toronto concluded that reserving up to an hour a day for physical activity in school curriculums does not detract from academic achievement. To the contrary, they noted that more exercise often improved school performance, despite the time it took away from reading, writing and arithmetic.

Exercise may benefit academic performance primarily by sharpening a particular set of cognitive functions, some researchers suggest. Many of these fall under the umbrella of executive function, the ability to plan and direct action. In a classroom setting, executive skills help students pay attention, decide when to take notes or ask questions, and organize their homework assignments. Participation in athletics is also thought to expand working memory—the capacity to hold items such as numbers and words in mind just long enough to mentally manipulate them. Exercise has a lesser effect—or in some cases none at all—on perceptual skills such as object recognition, language fluency, and the ability to visualize and mentally manipulate objects or spaces, studies show.

Kids may have to cross a minimum threshold of exertion before they reap cognitive benefits from exercise. In 2007, for example, clinical health psychologist Catherine L. Davis, also at Georgia, along with Tomporowski and their colleagues, randomly assigned 94 overweight children between the ages of seven and 11 to either no exercise time, 20 minutes or 40 minutes of aerobic exercise, such as running and jumping rope, five days a week. Before and after 15 weeks of this program, the children took a standardized test that measured their ability to plan, pay attention and process information. The children in the 40-minute program improved significantly on the planning component, but those assigned to 20 minutes of exercise—as with those required to do nothing at all—did not improve on any measure.

Scientists do not yet know exactly how much and what kind of aerobic exercise—team sports, running or biking—most influences intellectual development. The studies differ widely in the kinds of athletics they measure or require, and it may be that any kind of activity that gets the heart pumping qualifies. In certain instances—those in which the exercise involved organized sports—practicing teamwork and game strategies might account for some of the effects of exercise on executive function. In general, kids at the lower end of the performance scale both physically and cognitively have a greater opportunity to benefit from working out than do those who are reasonably competent in the classroom and the gym.

In addition to regular exercise, brief periods of movement can improve kids’ concentration. In 2006 education researcher Matthew T. Mahar of East Carolina University and his colleagues reported giving 243 North Carolina third- and fourth-grade students a daily 10- to 20-minute activity break in school. Teachers asked the children to stand up and play energetic games involving clapping, jumping, stomping or other movements. Trained raters observed the children before, during and after four to eight weeks of the drills, measuring their on-task behavior—paying attention to the teacher, participating in class discussions, and so on. The researchers found that by participating in the program, the children stayed on-task during academic instruction an average of 8 percent more than before. The most distractible students improved their attention spans by 20 percent. Thus, not only do lasting changes in fitness improve performance, but simply giving children a chance to move during the school day can enhance their ability to learn.

Brain-Building Workouts
Although scientists still do not know exactly why exercise benefits the brain, animal studies hint that physical activity may spur the growth of neurons in brain regions important to memory and executive function. Studies dating back to the 1970s showed that rats raised in spacious cages furnished with toys, branches to climb, and other objects to stimulate them physically and mentally develop a thicker cerebral cortex, a brain area that handles high-level reasoning and decision making (among many other functions). Rats that showed these brain changes performed better on memory tasks than did animals raised in small, empty cages. The rodents in these studies benefited from both physical exertion and mental stimulation, however, making it unclear which contributed to cognitive changes—or if both factors did.

More recently, scientists have begun to discover specific brain chemicals that might spur the improvements in mental fitness. Neuroscientist Henriette van Praag of the National Institute on Aging in Baltimore and her colleagues, among other research teams, have discovered that exercise increases the amount of key proteins that help to build the brain’s infrastructure for learning and memory in mice. These molecules include vascular endothelial growth factor (VEGF), which fuels blood vessel growth, and brain-derived neurotrophic factor (BDNF), which facilitates the development of the long extensions of neurons called axons that link one cell to the next. Such biological carpentry can create or fortify large brain networks that exchange and process information.

Specifically, physical activity may prompt construction in a part of the hippocampus called the dentate gyrus. The hippocampus is often likened to a switchboard in the brain that acts in the service of memory, tying thoughts together so that they stick in the mind [see “Making Connections,” by Anthony Greene; Scientific American Mind, July/August 2010]. In a study published in 2008 neurobiologist Shu-jie Lou and his colleagues at Shanghai University trained five-week-old juvenile rats by letting them run on an exercise wheel in their cage. (A healthy rat can easily run several miles a day.) After one week, brain cells in the dentate gyrus of these rats contained higher levels of VEGF, BDNF and other molecules that promote neuron growth than did comparable brain areas in rodents that had not run. Yet excessive running proved counterproductive: after a week of wheel spinning several hours per day, the concentration of neural growth factors in the hippocampus dipped. Thus, extreme forms of exercise might be less intellectually stimulating than more moderate physical activity.

Some evidence suggests that neural growth factors rise after aerobic exercise in humans, too. In 2008 psychiatrist Cindy Law of the University of Hong Kong and her colleagues found that a single 15-minute stepping exercise increased BDNF levels in the blood serum of 16 volunteers. (These levels are typically reduced in psychiatric syndromes such as depression in which neuronal growth and reconstruction are also stunted, suggesting that serum levels correspond with levels in the brain.) And yet, just as in rats, extensive vigorous exercise can have the opposite effect. In another small 2008 study epidemiologist Shuzo Kumagai of Kyushu University in Japan and his colleagues documented diminished BDNF concentrations in 12 men who engaged in activities such as distance running or tennis for more than 16 hours a week over more than three years as compared with 14 sedentary individuals.

Of course, not every kid can be a star athlete, and to succeed in school many children must opt for doing homework instead of running in the yard for hours on end. But parents should encourage their kids to squeeze some exercise into their busy days. And educators should recognize that physical education is about building the brain as well as the body and should put it center stage in the curriculum. If teachers want their students to pay attention, they should consider letting them jump, stomp and bend their bodies regularly during the school day. Most children have a natural inclination to move, so all the adults have to do is get out of their way.