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 centre 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 as if the differences are racial, the researchers believe they are really biological.
Blacks, they note, tend to have a slightly higher centre of gravity than whites, due to their having longer limbs with smaller circumferences. Because Asians and whites tend to have longer torsos, their centres 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 centre 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 centre of gravity, they add, but that benefit is cancelled out by the fact that they are usually not as tall as white swimmers.
"Locomotion is essentially a continual process of falling forward," study co-author Adrian Bejan said.
"Mass that falls from a higher altitude falls faster. In running, the altitude is set by the location of the centre 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 a part in what athletes excel at.
"When I grew up in South Carolina, we were discouraged from swimming," Edward Jones, a co-author, said.
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."