Stronger, Faster, Smarter

The stereotype of the "dumb jock" has never sounded right to Charles Hillman. A jock himself, he plays hockey four times a week, but when he isn't body-checking his opponents on the ice, he's giving his mind a comparable workout in his neuroscience and kinesiology lab at the University of Illinois. Nearly every semester in his classroom, he says, students on the women's cross-country team set the curve on his exams. So recently he started wondering if there was a vital and overlooked link between brawn and brains—if long hours at the gym could somehow build up not just muscles, but minds. With colleagues, he rounded up 259 Illinois third and fifth graders, measured their body-mass index and put them through classic PE routines: the "sit-and-reach," a brisk run and timed push-ups and sit-ups. Then he checked their physical abilities against their math and reading scores on a statewide standardized test. Sure enough, on the whole, the kids with the fittest bodies were the ones with the fittest brains, even when factors such as socioeconomic status were taken into account. Sports, Hillman concluded, might indeed be boosting the students' intellect—and also, as long as he didn't "take a puck to the head," his own.

Hillman's study, which will be published later this year, isn't definitive enough to stand alone. But it doesn't have to: it's part of a recent and rapidly growing movement in science showing that exercise can make people smarter. Last week, in a landmark paper, researchers announced that they had coaxed the human brain into growing new nerve cells, a process that for decades had been thought impossible, simply by putting subjects on a three-month aerobic-workout regimen. Other scientists have found that vigorous exercise can cause older nerve cells to form dense, interconnected webs that make the brain run faster and more efficiently. And there are clues that physical activity can stave off the beginnings of Alzheimer's disease, ADHD and other cognitive disorders. No matter your age, it seems, a strong, active body is crucial for building a strong, active mind.

Scientists have always suspected as much, although they have not been able to prove it. The idea of the "scholar-athlete" isn't just a marketing ploy dreamed up by the NCAA; it goes back to the culture of ancient Greece, in which "fitness was almost as important as learning itself," says Harvard psychiatrist John Ratey. The Greeks, he adds, were clued into "the mind-body connection." And they probably intuited a basic principle that Western researchers also figured out long ago: aerobic exercise helps the heart pump more blood to the brain, along with the rest of the body. More blood means more oxygen, and thus better-nourished brain cells. For decades, that has been the only link between athletic and mental prowess that science has been able to demonstrate with any degree of certainty. "People have been slow to grasp that exercise can really affect cognition," says Hillman, "just as it affects muscles."

Now, however, armed with brain-scanning tools and a sophisticated understanding of biochemistry, researchers are realizing that the mental effects of exercise are far more profound and complex than they once thought. The process starts in the muscles. Every time a bicep or quad contracts and releases, it sends out chemicals, including a protein called IGF-1 that travels through the bloodstream, across the blood-brain barrier and into the brain itself. There, IGF-1 takes on the role of foreman in the body's neurotransmitter factory. It issues orders to ramp up production of several chemicals, including one called brain-derived neurotrophic factor, or BDNF. Ratey, author of the upcoming book "Spark: The Revolutionary New Science of Exercise and the Brain," calls this molecule "Miracle-Gro for the brain." It fuels almost all the activities that lead to higher thought.

With regular exercise, the body builds up its levels of BDNF, and the brain's nerve cells start to branch out, join together and communicate with each other in new ways. This is the process that underlies learning: every change in the junctions between brain cells signifies a new fact or skill that's been picked up and stowed away for future use. BDNF makes that process possible. Brains with more of it have a greater capacity for knowledge. On the other hand, says UCLA neuroscientist Fernando Gómez-Pinilla, a brain that's low on BDNF shuts itself off to new information. In his experiments, rats were put through weeks of running on a wheel, a workout that increased their BDNF levels. Gómez-Pinilla left half of the animals alone; in the other half, he blocked the chemical's effects with a drug. Then he subjected both groups of athletic rats to a test of wits, encouraging them to find an object that was hidden underwater. The first group easily pinpointed its location, but the second, BDNF-deprived group wasn't nearly as quick or sharp. Nature has conducted a similar experiment on humans. In unlucky people with a faulty variant of the gene that makes BDNF, the brain has trouble both creating new memories and calling up old ones.

Most people maintain fairly constant levels of BDNF in adulthood. But as they age, their individual neurons slowly start to die off. Until the mid-'90s, scientists thought the loss was permanent—that the brain couldn't make new nerve cells to replace the dead ones. But animal studies over the last decade have overturned that assumption, showing that "neurogenesis" in some parts of the brain can be induced easily with exercise. Last week's study, published in the Proceedings of the National Academy of Sciences, extended that principle to humans for the first time. After working out for three months, all the subjects appeared to sprout new neurons; those who gained the most in cardiovascular fitness also grew the most nerve cells. This, too, might be BDNF at work, transforming stem cells into full-grown, functional neurons. "It was extremely exciting to see this exercise effect in humans for the first time," says Scott Small, a Columbia University Medical Center neurologist who coauthored the study with Salk Institute neurobiologist Fred Gage. "In terms of trying to understand what it means, the field is just exploding."