By Shankar Vedantam
Monday, August 11, 2008
If American sprinters Tyson Gay and Walter Dix reprise their race in the U.S. Olympic trials at the Olympic finals in Beijing, you will see the athletes crouch low over the starting blocks. Gay's right foot will be in the rear position on the blocks; Dix prefers to have his left foot in the rear position.
It might be a little awkward, but someone ought to tap Dix on the shoulder and tell him to consider switching the position of his legs. And not just Dix -- every sprinter in the Olympics ought to think about starting with his or her right foot in the rear position.
That's the surprising conclusion of an unusual new piece of research that ties sprinters' speed off the starting blocks with the structure of the human brain. All athletes, both experienced runners and novices, appear to be faster getting off the blocks when they start with the right foot in the rear position, regardless of whether they are right-footed or left-footed, and also whether they are used to a particular stance.
As nearly everyone knows, the human brain is divided into two hemispheres. Each hemisphere largely controls the movement of the opposite side of the body -- your left hemisphere moves your right hand and leg, while your right hemisphere directs your left side.
It has also been known for years that this hemispheric division of labor produces a minute difference in two aspects of movement: how quickly you can start to do something, and how quickly you can carry out the movement.
The difference seems to arise because the right hemisphere of the brain also plays a central role in reaction time, whereas the left hemisphere of the brain plays a larger role in overall movement control. When a task is primarily about reaction speed, people tend to be faster with their left hand because it takes less time for the right hemisphere to "talk to itself" than to tell the left hemisphere to move the right hand or foot.
But when it comes to movement -- in the case of sprinters, coming off the blocks and beginning the first step -- people tend to be faster with the right hand and foot. That's because the left hemisphere plays a dominant role in movement generally and moving the right side in particular.
These differences in speed are so minute, however, that people usually do not notice them.
Enter Adam Eikenberry. A sprinter in Canada, he started wondering a few years ago whether the left-right differences in reaction time and movement time could affect how quickly a sprinter gets off the blocks.
A 100-meter sprint provides a unique laboratory for the experiment because it happens to be one of those rare settings which involve both reaction speed -- how quickly sprinters can respond to the gun going off -- and movement speed -- how quickly they can clear the blocks. Minute time differences, moreover, actually matter.
If differences in reaction and movement time affected how sprinters got off the blocks, the two effects ought to run in opposite directions. A sprinter should react faster with his left leg in the rear position but move through the blocks faster with his right leg in the rear.
Eikenberry and Jim McAuliffe, a cognitive psychologist who now works at Nipissing University in North Bay, Ontario, brought in a number of runners to their laboratory. Half were experienced sprinters, and the other half had never used starting blocks. A team of researchers had the volunteers take off 48 times -- half the starts with the right leg in the rear position, and half the starts with the left leg in the rear position.
Eikenberry guessed that there would be a difference among novices but that experienced sprinters would be faster getting off the blocks using the stance they were used to. He was wrong. Every volunteer cleared the blocks faster with the right foot in the rear position.
"In a 10-second race, the time people take to leave the blocks is half a second, or 5 percent of the entire race," said Eikenberry, who now works as a kinesiologist in Ottawa. "Any time that you can save in that 5 percent gives you that much of an advantage."
The researchers found an 80-millisecond advantage on average when sprinters had their right foot in the rear position. That's nearly a tenth of a second -- the difference between gold and ignominy.
McAuliffe, who published the study in the journal Acta Psychologica, hypothesized that while people were indeed faster reacting to the sound of the gun when their left leg was in the rear position, most of the time spent clearing the starting blocks involved moving through the blocks, where the right foot in the rear position provided an overwhelming advantage.
It is important to note that the research does not suggest that sprinters who start with the right leg in the rear position on the blocks will necessarily beat sprinters with the left leg in the rear position. The data do suggest that sprinters with a left-footed stance might improve their time by switching to a right-footed stance. Still, another co-author of the paper, Ian Newhouse, who ran the 400-meter hurdles for Canada at the 1984 Los Angeles Olympics, said the intriguing result points to the need for additional research on a real running track, rather than in a laboratory.
"The difference between the top eight finishers is often less than 80 milliseconds," McAuliffe added. "It can make the difference between winning and losing the race."