Double amputee Oscar Pistorius, who runs on artificial legs made of carbon fiber, definitely sprints differently than intact-legged elite runners, according to newly released research. While he appears to have no clear advantage over runners with two legs, it remains uncertain how individual components of his unique stride affect his speed. Even the scientists who carried out the research disagree about how to interpret the findings, highlighting just how difficult it is to identify the variables that are most important for sprint speed.

"We found that the amount of metabolic energy and his rate of fatigue were not distinct from runners with intact limbs," says Hugh Herr, director of the Biomechatronics Group at the MIT Media Lab and one of the scientists involved in the study. "However, his biomechanics were distinct from intact-legged runners."

Pistorius, a South African sprinter, has been at the center of a high-profile battle over whether athletes with prostheses should be allowed to compete against intact-limbed athletes in events including the Olympics. Pistorius, nicknamed "the Blade Runner" because of his J-shaped Cheetah Flex-Foot carbon fiber artificial limbs, has set a number of Paralympic world records, and in 2007 he placed second in the South African National Championships--an able-bodied event. His impressive performances have made some wonder whether prostheses specially designed for running might give amputees a special advantage.

In the spring of 2007, the International Association of Athletics Federations (IAAF), the international governing body for athletics, instituted a rule prohibiting the use of technical devices that might give athletes a competitive advantage, and later prohibited Pistorius from participating in competitions under its rule. Pistorius appealed the decision, enlisting the aid of several U.S. scientists, and the Court of Arbitration for Sport (CAS), an international arbitration body, ruled that the IAAF had not provided sufficient evidence to show that the blades gave him an advantage. It reversed the ban in May 2008, enabling Pistorius to try out for the 2008 Olympics. (He narrowly failed to qualify for the South African team in the 400-meter dash.) The U.S. researchers have now published the results of their study in the Journal of Applied Physiology.

According to Peter Weyand, a physiologist and biomechanist at Southern Methodist University, in Dallas, and lead author of the study, much of Pistorius's hearing focused on the wrong issue. "There was a lot of attention given to the question of whether his blades allowed him to run with less energy than other runners, which is pretty much irrelevant in sprinting," says Weyand. "It's sort of like arguing that a Volkswagen will beat a Porsche in a drag race because it gets better gas mileage." Fuel economy is not the determining factor in sprint races, he explains: "When sprinting, animals are not energy limited; the mechanics are the limiting factor."

Weyand's study does, however, suggest that Pistorius has different running mechanics than intact-legged runners do: he hits the ground with much less force and stays in contact with the ground longer, a pattern that previous research suggests would put him at a disadvantage. "We know from past experiments that what separates really fast runners is how hard they can hit the ground in relation to their body weight," says Weyand.