Usain Bolt, a Jamaican sprinter who holds the world record for 100 and 200 meters, is considered the fastest person alive, and perhaps ever recorded. He isn’t the only athlete from Jamaica who’s been incredibly successful, however – the small nation has been home to a slew of sprinters.

So scientists decided they wanted to find out why Jamaicans in particular were such swift runners. They examined how symmetry in body parts played a role in the speed of runners – especially symmetrical knees. Body symmetry has previously been thought to be a sign of good fitness and physical development, and associated with speed, attractiveness, and sperm production.

The study’s findings mirrored these long-held beliefs: the researchers found that Jamaicans who had symmetrical knees were particularly good at sprinting. “We found that Jamaican children have particularly symmetric legs, in comparison to Europeans,” Professor John Manning of Northumbria University in the U.K., said. “Furthermore, in children symmetry in the legs, particularly in the knees, predicted their willingness to sprint and their sprinting times when they were adults.”

Professor Manning and his team began the research project in 1996, and studied some 300 primary school children from rural Jamaica. The participants had an average age of 8 at the beginning of the project; the researchers measured their body symmetry and then followed up years later with tests for handedness and aggression, among others. In 2010, 168 of the participants agreed to do sprinting tests in their early twenties.

Professor Manning noted that the purpose of the study was to examine fluctuating asymmetry (FA), or the small deviations from symmetry in the body. “These are measured from about 10 pairs of traits such as knee width, ankle circumference, food length, ear height, finger length, etc,” Manning told the Independent. He notes that the majority of people usually have little deviations from symmetry throughout each trait.

“[W]e think our results inform the debate as to why Jamaicans tend to win gold medals in sprinting,” Manning told the Independent. “However, to be sure we need to follow it up by looking at international level sprinters and adding some genetic tests.” The researchers plan to analyze both male and female Jamaican athletes as they continue to analyze the role of body symmetry in fitness.