Michael Phelps’ Olympic success may come down to biology.

Some academics took a look at the record books from the past 100 years and the bodies of the athletes and made this determination. It wasn’t about race, but body type – though the fastest sprinters tended to be of West African ancestry and the fastest swimmers tended to be white.

A Duke engineer and a couple of fellow researchers say it’s about an athlete’s center of gravity. The center tends to be slightly higher in the bodies of blacks (longer limbs and smaller circumferences) than whites (longer torsos) – giving an advantage to blacks in running and an advantage to whites in swimming.

“Locomotion is essentially a continual process of falling forward,” said Adrian Bejan, professor of engineering at Duke's Pratt School of Engineering and a study author. “Body mass falls forward, then rises again. 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.”

This is not to say there aren’t cultural factors, such as lack of access to swimming pools and lower socioeconomic status, said Edward Jones, a Ph.D. candidate at Cornell University who is teaching at Howard University and was another study author.

And, he said, encouragement can make the difference. “Just look at the Williams sisters in tennis or Tiger Woods in golf.”

Associated Press photo of Michael Phelps