When you think about building the perfect sprinter, you might think of long legs and powerful muscles. But new research published in the Journal of Experimental Biology suggests that it's the size of an athlete's heels that might also be important in giving them the edge.
This is research by Stephen Piazza and his team in the US, who was approached by an American Football star to find out if they could help them get the edge over the competition. When a sprinter pushes off the ground, their acceleration depends on the leverage that they can generate by the calf muscles pulling on the back of the heel, pulling it up and pushing the toes down.
Piazza figured that the best sprinters would have a long distance between the ankle and the back of the heel – making a longer, more powerful lever and pulling the heel up a long way. But when they actually measured how far the athlete's tendon actually moved while pulling up, they got a surprising result.
The researchers discovered that this particular footballer's tendons moved a much short than average distance. So they measured the tendons of a number of elite sprinters and long jumpers, and compared them with the legs of non-sporting people. And they found that on average, the distance athlete's tendons moved with 25% less than those of non-sporty types, suggesting they actually had a shorter “heel lever”.
When Piazza looked into this, he discovered that sprinters compensate for this by contracting their calf muscles comparatively more slowly than those of non-sprinters, generating much more force when accelerating. This is a similar design to many sprinting animals. And the scientists also found that sprinters toes were on average a centimetre longer, meaning they stay in contact with the ground longer as the sprinter pushes. So although it appears on first glance that short heels might not help you to sprint, short heels combined with long toes and powerful muscles actually help to generate more power.