To be a swift runner you need strong muscles, a powerful heart, determination and — symmetrical knees? That’s what scientists learned when they studied some of the world’s top sprinters.
Science has shown that animals and people with more symmetrical bodies tend to be stronger and healthier than those who are a bit lopsided. But this is the first time researchers have been able to predict who will be the fastest runners just by measuring their knees.
“Among the very best sprinters in the world, knee symmetry predicts who’s going to be the best of the best,” says Robert Trivers of Rutgers University in New Brunswick, N. J. As an evolutionary biologist, he studies how organisms have adapted over generations to their environments.
His team published its new findings online November 17 in the journal PLOS ONE.
Trivers knew symmetrical knees could aid runners. In an earlier study, he showed that children who at age 8 had more symmetrical knees developed into the fastest runners by the time they were 22. Now he wanted to know why symmetry made such a difference in top athletes.
To find out, he brought a team of researchers to the island nation of Jamaica in the Caribbean. They measured the knees, ankles, and feet of 73 elite sprinters at the MVP Track and Field Club in Kingston. Jamaican Shelly-Ann Fraser-Pryce was among the athletes studied. She won Olympic gold medals in the 100-meter (328-foot) sprint in both 2008 and 2012.The researchers then took the same measurements from 116 local non-runners who were about the same ages and sizes as the elite athletes.
“Elite sprinters had more symmetrical knees than normal people,” Trivers says. “Their ankles were also slightly more symmetrical.” But their feet were not special. “It seems the feet are completely irrelevant,” he concludes.
Then the researchers took a closer look at the athletes. They asked the club to give them the best times for each of the runners in their chosen events: the 100-, 200-, 400-, or 800-meter races. In every case, Trivers’ group found, the very fastest runners had more symmetrical knees than their competitors. And runners who competed in the 100-meter event had the most symmetrical knees of all.
That’s not so surprising. When people run down a track, their knees pump up and down, pushing them forward. Having symmetrical knees allows an athlete to run more efficiently. And unlike longer events, where the runner has to make two or more left-hand turns to corner around the track, sprinters have only a straightaway to speed down.
The study is important because it adds to long-term research about how symmetry affects our bodies over the course of our lifetime, says John Manning. He’s an evolutionary biologist at Northumbria University in Newcastle-upon-Tyne, England. The new study also raises some interesting questions, he adds. For example: Do runners have symmetrical legs because of good genes, or because of all the time they spend exercising?
Trivers says his earlier study of children makes him think at least part of the answer comes down to the bodies our genes gave us. But he wants to find out more. He plans to return to Jamaica every two years to measure the athletes’ knees and speed. His goal: to probe if — and how — those measurements might change over an athlete’s career.
Indeed, he explains, “We’re planning to do more work to find out if knees get more symmetrical with intense training.”
evolutionary biologist Someone who studies the adaptive processes that have led to the diversity of life on Earth.
sprint To run at top speed over a fairly short distance. In competitive running, the 100-meter race is a sprint.
symmetry In geometry, the property of being indistinguishable from a shifted, rotated or reflected image of the same object. For example, the letter “X” looks the same whether reflected in a mirror or turned upside down — two different kinds of symmetry.