A new study has made an extraordinary claim about sporting success: it's all in the belly button.
Scientists claim that the position of the belly button shows the body's centre of gravity, and that a person's centre of gravity rather than their height or weight determines whether they will have a better natural advantage in running or swimming.
And professor Andre Bejan of Duke University claims that the report explains why black athletes tend to dominate Olympic sprinting events while white athletes tend to sweep the medals in the pool.
"What matters is not total height but the position of the belly-button, or centre of gravity," explained Bejan, the lead author of the study, which was published in the International Journal of Design and Nature and Ecodynamics.
"It so happens that in the architecture of the human body of West African-origin runners, the centre of gravity is significantly higher than in runners of European origin," he said.
Bejan explained that this difference gives individuals of West African origin - whose belly buttons are on average three centimetres higher than European-origin athletes - an advantage in sprinting on the track, since their higher centre of gravity helps them run forwards.
"Locomotion is essentially a continual process of falling forward, and mass that falls from a higher altitude, falls faster," Bejan explained.
Conversely, European-origin athletes have a similar benefit in swimming since longer torsos help them cut through the water.
"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 per cent longer torso than West Africans, which gives them a 1.5 per cent speed advantage in the pool."
Bejan added that Asians have similar length torsos as Europeans, but their generally shorter height is a disadvantage in the pool.
The study looked at 100 years of records in sprinting and freestyle swimming events from both men and women, focusing on athletes geographic origins and biology, not race, in order to tackle what the authors refer to as the "obvious" race angle in why black athletes dominate sprinting and white athletes swimming.