What makes an athlete fast may have more to do with body type than training. Researchers from Duke University and Howard University think the secret may lie in the body's center of gravity.

Their study, released online in the International Journal of Design and Nature and Ecodynamics, may explain why the fastest sprinters are usually black, while the fastest swimmers are usually white, a difference that goes back decades. Though on the face of it this may seem like the differences are racial, the researchers believe they're really biological.

Blacks, they note, tend to have a slightly higher center of gravity than whites, due to having longer limbs with smaller circumferences. Because Asians and whites tend to have longer torsos, their centers of gravity are lower.

Those differences may translate into faster times in specific sports. Looking at other studies on the human body, the researchers deemed that, on average, blacks have about a 3% higher center of gravity than whites. That may make black sprinters 1.5% faster than white sprinters. Using that formula, whites may have a similar advantage over blacks in swimming. Asians may have an even greater advantage than whites in terms of center of gravity, they add, but that benefit is canceled out by the fact that they’re usually not as tall as white swimmers.

"Locomotion is essentially a continual process of falling forward," study co-author Adrian Bejan, in a news release. "Mass that falls from a higher altitude falls faster. In running, the altitude is set by the location of the center of gravity. For the fastest swimmers, longer torsos allow the body to fall forward farther, riding the larger and faster wave." Bejan is a professor of engineering at Duke's Pratt School of Engineering.

But the authors don't ignore the role that environment, as well as biology, may play in what athletes excel at.

"When I grew up in South Carolina, we were discouraged from swimming," Edward Jones, a co-author, said in a news release. Jones, who teaches at Howard University and is black, added, "There wasn't nearly as much encouragement for us as young people to swim as there was for playing football or basketball. With the right encouragement, this doesn't always have to be the case -- just look at the Williams sisters in tennis or Tiger Woods in golf."

-- Jeannine Stein

Photo: Jamaican sprinter Usain Bolt, left, is an Olympic medalist and world record holder. Photo credit: Fabrice Coffrini / AFP/Getty Images