- Belly-button placement can give some athletes a competitive advantage over others.
- The placement of the navel varies among athletes of different ethnic origins.
- Whether an athlete had an innie or an outie didn't affect performance.
Scientists have found the reason why some athletes dominate on the running track and others in the swimming pool: It's in their belly buttons, a study published Monday shows.
What's important is not whether an athlete has an innie or an outie but where his or her navel is in relation to the rest of the body, says the study published in the International Journal of Design and Nature and Ecodynamics
The navel is the center of gravity of the body, and given two runners or swimmers of the same height, one black and one white, "what matters is not total height but the position of the belly button, or center of gravity," Duke University professor Andre Bejan, the lead author of the study, told AFP.
"It so happens that in the architecture of the human body of West African-origin runners, the center of gravity is significantly higher than in runners of European origin," which puts them at an advantage in sprints on the track, he said.
Individuals of West African-origin have longer legs than European-origin athletes, which means their belly buttons are three centimeters (1.18 inches) higher than whites', said Bejan.
That means the black athletes have a "hidden height" that is three percent greater than whites', which gives them a significant speed advantage on the track.
"Locomotion is essentially a continual process of falling forward, and mass that falls from a higher altitude, falls faster," Bejan explained.
In the pool, meanwhile, whites have the advantage because they have longer torsos, making their belly buttons lower in the general scheme of body architecture.
"Swimming is the art of surfing the wave created by the swimmer," said Bejan.
"The swimmer who makes the bigger wave is the faster swimmer, and a longer torso makes a bigger wave. Europeans have a three-percent longer torso than West Africans, which gives them a 1.5 percent speed advantage in the pool," he said.
Asians have the same long torsos as Europeans, giving them the same potential to be record-breakers in the pool.
But they often lose out to whites because whites are taller, said Bejan.
Many scientists have avoided studying why blacks make better sprinters and whites better swimmers because of what the study calls the "obvious" race angle.
But Bejan said the study he conducted with Edward Jones, a professor at Howard University in Washington, and Duke graduate Jordan Charles, focused on the athletes' geographic origins and biology, not race, which the authors of the study call a "social construct."
Bejan is white, originally from Romania, and Jones is black, from South Carolina.
They charted and analyzed nearly 100 years of records in men's and women's sprinting and 100-meter freestyle swimming for the study.