Elite sprinters may be helped by unusual foot anatomy.
When feet are made for sprinting. I'm Bob Hirshon and this is Science Update.
Some track coaches say sprinters are born, not made. Penn State University researchers have found some truth in that. Kinesiologists Steve Piazza and Sabrina Lee compared the feet and ankles of top college sprinters to those of non-sprinters. Piazza says a key section of the Achilles' tendon was shorter in the sprinters.
When your Achilles' tendon attaches closer to your ankle joint, it also permits your muscle to shorten more slowly. And when that happens, the muscle is able to generate more force.
The sprinters also had long toes, which means that their feet stay in contact with the ground longer than average. And pushing harder and longer against the ground helps a sprinter accelerate at the start of a race. Piazza says this anatomy is even more pronounced in the cheetah, the best sprinter on earth. I'm Bob Hirshon for AAAS, the Science Society.
Making Sense of the Research
A lot goes into making a star athlete, including talent, dedication, a fitness regime, lots of practice, and a little luck. Of course, no one would deny that having the right kind of body can help, especially at elite levels. As an obvious example, the average height of an NBA basketball player is about 6 feet 7 inches. That's taller than about 99 percent of adult men, and more than 9 inches taller than the average American man. Since being taller makes it easier to dunk, shoot, and block, the tallest players tend to rise to the top of the game. As a result, only men who are extraordinarily tall have even a fighting chance of making it all the way to the NBA.
However, an athlete's body can confer advantages in less obvious ways. Olympic swimming star Michael Phelps, for example, has a number of physical advantages that make his body perfectly suited for competitive swimming, including an extremely wide arm-span that adds power to every stroke, and unusually flexible ankle joints that make his kicks extra-propulsive. Other elite swimmers may not be built as ideally as Phelps, but their bodies probably resemble his much more than the average person's.
In this study, the researchers compared the structure of sprinters' feet and ankles to those of non-sprinters. They found a number of differences, and then modeled the effect of these differences on computers. One difference was in a key part of the Achilles' tendon, which connects the calf muscle to the heel bone. The part of the tendon in question, called the lever arm, was about 25 percent shorter in top sprinters than in non-sprinters. A shorter lever arm actually makes the ankle less flexible. However, it also means that the calf muscle can contract more slowly as it pulls the heel off the ground, because it's tethered more closely to the heel itself. And when a muscle can contract more slowly, it can exert more power, because the contracting muscle's fibers have more time to create structures called "cross-bridges" that generate force. The upshot? The shorter tendon structure trades some flexibility for a bigger payoff in power.
Sprinters' feet also had longer toes than the average foot. This, too, gave them extra power. That's because your foot can only push you forward when it's actually in contact with the ground—not while it's lifted in the air. And feet with longer toes stayed in contact with the ground for a split second longer on every step. That adds up to a significant amount of extra forward motion in just a few seconds.
These two key advantages, Piazza concludes, give sprinters an advantage at the crucial start of the race, which is when sprints are essentially won or lost. A marathon runner, on the other hand, would see little benefit from this kind of foot structure, and may even suffer a disadvantage: for example, a less flexible foot that stays in contact with the ground longer may suffer more wear and tear over a distance. So it's very possible that the shape of a runner's foot not only may determine her success in the sport, it might even direct her towards one kind of running versus another.
Now try and answer these questions:
- How are sprinters' feet different from the average foot?
- How do these structural differences create an advantage for the sprinter?
- Can you think of other physical attributes that can be useful for a particular sport?
- Cheetahs have extremely long toes and short ankle tendons, compared with similar animals. How does this bolster Piazza's findings in human sprinters?
You may want to check out the November 25, 2009 Science Update Podcast to hear further information about this Science Update and the other programs for that week. This podcast's topics include: satellites for human rights, a sprinter's anatomical advantage, the face of aggression, and newborns with accents.