Any school kid can tell you: nerds are not usually the most athletic specimens. But a new study suggests that young men who are physically fit tend to be more intelligent. The results appear in the Proceedings of the National Academy of Sciences.

Animal studies have long shown a link between physical activity and better memory. And in humans, aerobic exercise has been found to boost cognitive function in the elderly. But studies in young adults have yielded conflicting results. Strenuous physical activity in adolescents actually seemed to make mind matters worse.

To try to settle the issue, scientists in Sweden reviewed the records of more than a million men who enlisted for military service at the age of 18. And they found that cardiovascular fitness, but not muscle strength, was associated with overall intelligence (at least as measured by the Swedish army). And when they consulted additional national databases, they found that physical fitness at the age of 18 also foreshadowed greater academic achievement later in life. Even among the twin pairs, the fitter brother tended to be the smarter.

So remember, a nerd may not be athletic.  But a lot of athletes may be harboring an inner nerd.

—Karen Hopkin