So Do Prosthetic Limbs Give Sprinters an Advantage Or Not? | Popular Science
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So Do Prosthetic Limbs Give Sprinters an Advantage Or Not?

After a year-long study of the case of Oscar Pistorius, two starkly opposing scientific camps emerge on each side of the debate

Oscar Pistorius

Using the same set of data--an analysis of double-amputee sprinter Oscar Pistorius and his carbon fiber Cheetah prosthetic legs--two teams of researchers have come to very different conclusions on whether his prostheses give him an advantage over sprinters with both of their legs.

The future of modern prostheses' usage in sports hangs in the balance, and the fight is getting ugly.

In a point-counterpoint published by the Journal for Applied Physiology today, Dr. Peter Weyand of Southern Methodist University and Dr. Matthew Bundle of the University of Wyoming claim sprinters' prosthetic legs can shave more that 10 seconds from a runner's 400-meter.

Dr. Rodger Kram of the University of Colorado and his colleagues' response: "You cannot be serious!"

In May 2008, the experts on both sides of the argument worked together to overturn the IAAF's ban on prosthetic legs in professional sprinting. The ban remains overturned, but now, with the data from an 18-month study made public, very different conclusions have arisen over what the data actually means. The question boils down to this: Is it the prostheses or raw athletic ability that allows South African double-amputee sprinter Oscar Pistorius to run so fast?

"Personally, I find it preposterous, ludicrous, to suggest that amputating my legs and giving me prostheses would make me run 12 seconds faster over 400 meters," says Kram. "Take away all the muscles in my calf and foot, and I'm going to run faster?"

Pistorius on the Track

Elvar Pálsson

The row started with Pistorius's appeal to overturn the IAAF's ban on prosthetic limbs. A research team, including Weyand and Bundle, examined the scientific reasoning behind the ban. "The evidence put forth by the IAAF wasn't scientifically supportable," Bundle explains. "But they didn't have the data then that we do now."

The ban was rescinded, but the new data seems little more conclusive as research team members draw lines in the sand. On one side Weyand and Bundle found what they believe is solid evidence that Pistorius's prostheses give him a clear advantage over other sprinters. But Kram, along with other colleagues that include Dr. Hugh Herr of MIT's Media Lab, claim "indisputable" evidence to the contrary.

"It's important to note that this is not a new study by Weyand and Bundle," Kram says. "It's an opinion piece that has not been peer reviewed."

The study Kram refers to is Weyand and Bundle's comparison of Pistorius to physiological data collected on other sprinters. "Oscar swings his legs faster than anyone we've ever seen in the history of sports or science," Bundle says. "In fact, it's significantly faster. If you compare Oscar to six of the former and current world record holders, he swings his legs 15 percent faster."

Kram and his colleagues at MIT have since been collecting data on a different set of sprinters – single-limb amputees – comparing the way they swing their natural legs to their artificial ones. "We decided that a study of unilateral amputees would provide good insight because you can compare the prosthetic leg to the biological one," he says. "It gave us good control."

They determined that prosthetic limbs produce lower ground reaction forces than those of the average sprinter, a fact Weyend and Bundle don't dispute. But Kram and company also argue that while Pistorius' leg repositioning time is swift, it's not unnaturally so. Rather, his repositioning speed is driven by his athleticism; Pistorius, through training, has compensated for reduced ground force with blazing leg speed.

Weyand and Bundle fire back that Pistorius's speed is in no way natural: "Even in comparison to individuals with the most extreme gait adaptations for speed in recorded human history, the double-artificial-limb value is not simply an outlier; it is quite literally off the biological charts," they write. This ease of acceleration could trim 12 seconds off a 400-meter runner's time.

Back and forth it goes. Kram and company cite Weyand's previous writings claiming vertical ground reaction force is the key determinant of sprinting speed. Weyand and Bundle respond that "more erect limb posture" in leg-amputees, coupled with lower ground force "co-reduce the muscular forces required to attain the same sprint running speeds to less than half of intact-limb levels," saying Pistorius needs half the strength to reach the same speeds as runners on biological legs. Kram and company respond with the affronted incredulity of a John McEnroe.

Neither side of the argument wants to see amputee sprinters banned from competition, but they have different visions for the future of the sport. Kram's side sees no problem letting amputees sporting Cheetahs take to the starting blocks. Weyand and Bundle suggest redesigning the prostheses to remove perceived advantages. "As for Oscar, there are some pretty simple things that could be done to his prostheses that could remedy the advantages that we've found," Bundle says.

Could an age of running where prostheses are approved for competition by sanctioning authorities solve the problem? It's possible, but not likely. Each runner is different and thus a standardized prosthetic would be difficult to implement. Further, how does a governing body put limits on how fast an athlete can reposition his legs and still call it an open competition?

The point-counterpoint article published today hopes to wring consensus from the scientific community. The piece will remain on the Web for months, soliciting responses from other scientists, some of which will be digested into another paper representing the feelings of the larger scientific community.

A rare point of agreement: more research is necessary. "When you think about it, the world has only studied one bilateral amputee runner, and he happens to be the fastest," Kram says. "One would think that before leveling an opinion on this, the scientific community should conduct more research."

Regardless of what further research shows, either prostheses will be banned from professional sprinting or they will be permitted in some form. The former outcome will dash the dreams of many, and the latter will invite skepticism that amputee sprinters' achievements are truly their own (Barry Bonds and the asterisk comes to mind). For athletes like Pistorius, that means waiting in athletic purgatory until science decides whether the lack of biological limbs constitutes a handicap or a performance enhancement.

For someone used to moving so fast, the wait must be interminable.

For more on the issue, definitely see double amputee sprinter Aimee Mullins's recent guest-edit stint at Gizmodo, and her piece Racing on Carbon Fiber Legs: How Abled Should We Be?

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