Dr Lee and Dr Piazza already knew that sprinters tend to have a higher proportion of fast-twitching muscle fibres in their legs than more sedentary folk can muster. (These fibres, as their name suggests, provide instant anaerobic pulling power, rather than the sustained, oxygen-consuming effort that is needed by longer-distance runners.) They suspected, though, that they would find differences in the bone structure as well. And they did.
They looked at seven university sprinters who specialise in the 100-metre dash and five 200-metre specialists, and compared them with 12 non-athletic university students of the same height. In particular, they looked at the sizes of bones of the toes and heel. They also used ultrasonic scanning to measure the sliding motion of the Achilles tendons of their volunteers as their feet moved up and down. This allowed them to study the length of the lever created by the tendon as it pulls on the back of the heel to make the foot flex and push off the ground.