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Do prosthetic legs give runner a competitive advantage?

Researchers studied Oscar Pistorius' abilities compared with able-bodied runners. The conclusion? It's up for debate.

July 06, 2009|Jeannine Stein

Oscar Pistorius is faster on two prosthetic legs than many athletes are on two intact legs, which makes some people believe those legs give the South African runner an advantage.

Controversy has been simmering about the curved Cheetah carbon fiber legs for some time, and a new study comparing various aspects of his athletic performance with that of able-bodied runners aimed to clarify the prostheses' benefits -- or lack thereof. Ultimately, it might make things muddier.

Pistorius had competed (and won medals) for years in the Paralympics, but in 2007 he ran in an international competition against able-bodied runners. Later that year, the International Assn. of Athletics Federations banned technical devices incorporating springs, wheels or other elements that could give a benefit to the user, although it denied the ban was linked to Pistorius.

Subsequently, scientists determined that the prosthetics did give Pistorius certain advantages, and in 2008 the athletic association decided he couldn't run in competitions against able-bodied runners. However, that ruling was overturned by the Court of Arbitration for Sport (a Swiss-based international arbitration organization that decides sports-related disputes) later that year, saying there wasn't enough evidence supporting the claims that the prosthetics gave Pistorius an edge. (Pistorius wanted to compete in the 2008 Olympics in either the 400 meters or the 4 x 400 relay, but did not qualify.)

What the Court of Arbitration saw was a study conducted by several researchers and done at the Locomotion Laboratory at Rice University in Houston. The results -- published in the June issue of the Journal of Applied Physiology -- did not conclusively say whether Pistorius' prosthetics gave him an advantage.

Three things were tested: how much energy Pistorius expended during running, how resistant he was to fatigue, and his sprinting mechanics. His results were compared with competitive male runners with intact limbs.

Pistorius runs slightly more economically than able-bodied runners, but the results were not statistically different, says Peter Weyand, associate professor of applied physiology and biomechanics at Southern Methodist University in Dallas and lead author of the study. However, Pistorius uses 17% less energy than sprinters. "That was exactly what I expected," he said. "He has 20% less limb musculature. Other athletes use their calf muscles to generate force, but he doesn't have that."

Different pacing

But that doesn't mean the South African runner is better off. "He does use less energy, but it's because he has less muscle," Weyand says. In a V02 max test (the maximum amount of oxygen, in milliliters, that the body uses in one minute, per kilogram of body weight), researchers found that while Pistorius used less energy than other sprinters to achieve his maximum, his maximum level was also comparatively lower by the same amount. "It's like he's a smaller car that uses less gas, but his engine is smaller in comparison," Weyand says.

Because Pistorius runs on blades and has no muscle fibers below the knee, some speculate he doesn't get as fatigued as other runners. Fueling that idea is the fact that able-bodied runners run the first half of a 400-meter race quickly, but finish more slowly. Pistorius' modus operandi is the opposite -- he opens slowly, due to a lack of ankles and Achilles tendons, but finishes fast.

"He looks faster at the end because he is," Weyand says. "Because his pacing is different from the intact-limb athletes, that fed into the idea that he's going to have better endurance and less fatigue."

In a treadmill test for this study, all runners began at a certain speed, eliminating the start. With this method, researchers concluded that Pistorius could hold his speed over longer sprint distances the same as able-bodied runners, leading them to believe he was no less fatigued than they were.

Pistorius appears to have different sprinting mechanics than his able-bodied counterparts. Previous tests have shown, Weyand says, that the amount of time it takes for someone to lift one leg off the ground and place it down again while running is virtually the same for everyone. "Slow pokes and speed demons are the same," Weyand says. "That's the way the system works -- you can't reposition them any faster. I expected [Pistorius] to conform."

But he didn't. He spent 34% less time in the air between steps and took 21% less time to reposition his limbs than the able-bodied runners. That, according to Weyand, is likely due to the fact that he has less mass because of the prostheses. But wait -- there's more.

Pistorius does not hit the ground as hard as runners who have intact limbs, again probably due to the lighter-weight prostheses. Also, his foot stays in contact with the ground 14% longer on each sprinting step.

Dispute on results

So -- drum roll -- do Pistorius' prosthetic limbs give him an advantage or not?

"I can't answer that question," Weyand says. "Those of us who conducted the test do not agree on that."

But he adds that more information will be revealed in another study to be released some time in the future.

"It's not at all a wash, so then it becomes a matter of interpretation," Weyand says. "Could he run that fast if he had biological limbs? Or, alternatively, if you took an average person and gave them blades, would they be able to swing their legs as fast?" Couple that with the fact that running prostheses will no doubt continue to evolve and, needless to say, this will surely be continued.


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