The emerging supremacy of artificial legs.

Science, technology, and life.
May 20 2008 1:00 PM

Leg Up

The emerging supremacy of artificial limbs.

Oscar Pistorius. Click image to expand.
Oscar Pistorius

Oscar Pistorius was born with defective legs. Before his first birthday, they were amputated below the knee. That didn't stop him. Now 21, he has broken three world track records for disabled athletes and is racing to qualify for the 400 meters at this summer's Olympics. If he can shave four-tenths of a second off his best time, he'll make it.

William Saletan William Saletan

Will Saletan writes about politics, science, technology, and other stuff for Slate. He’s the author of Bearing Right.

How has he done it? One answer is superhuman grit. The other is superhuman legs. Pistorius runs on carbon-fiber prostheses made for sprinting. In January, the International Association of Athletics Federations declared them ineligible, claiming they were better than human legs. But on Friday, the Court of Arbitration for Sport overturned that decision, clearing his path to the Olympics.

Go, Oscar, go. We're all rooting for you to cross that finish line in Beijing. Just one note of caution: Don't win.

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That's the strange upshot of the court's ruling. Artificial legs are fine to run on, as long as you don't win the race.

How did we get to this awkward place? The story begins last year, when the IAAF adopted a rule prohibiting "any technical device that incorporates springs, wheels or any other element that provides the user with an advantage over another athlete not using such a device." According to the court, the IAAF interpreted this rule as banning any device that provides "any advantage, however small, in any part of a competition."

In November, the IAAF tested Pistorius and his artificial legs against similar sprinters on human legs. The scientist who supervised the test reported, "Energy return was clearly higher in the prostheses than in the human ankle joints." He also found that "fast running with the … prosthesis is a different kind of locomotion than sprinting with natural human legs. The 'bouncing' locomotion is related to lower metabolic cost."

The court didn't dispute these findings. It conceded that the artificial legs generated a "flatter" running motion and cost Pistorius "less metabolic energy." But it rejected the IAAF's interpretation of the rule. The word advantage, the court decided, has to mean "overall net advantage"—i.e., "more disadvantages than advantages." In other words, it's OK to use artificial legs, even if they're better than human legs at some things. In fact, they're already better at some things. They just can't be better at everything.

On this basis, the court rejected the IAAF's tests. The tests focused on the straight part of the race, where the artificial legs gave Pistorius an edge. They left out the initial "acceleration phase" and the first bend, where his legs put him at a disadvantage. They also failed to show that his flatter motion or lower metabolic cost produced a net benefit.

In short, the court found that none of the tests conducted on Pistorius, even by his own experts, "quantified all of the possible advantages or disadvantages" of his legs. If you read the opinion, it becomes clear that this task is essentially impossible. There are too many variables.

How, then, can we settle the question of net advantage? By running the race. The court pointed out that the same artificial legs, manufactured and sold to other amputees, have "been in use for a decade, and yet no other runner using them … has run times fast enough to compete effectively against able bodied runners." It concluded: "In effect, these prior performances by other runners using the prosthesis act as a control for study of the benefits of prosthesis and demonstrate that even if the prosthesis provided an advantage … it may be quite limited."

In other words, there's nothing to complain about until runners with artificial legs start winning.

That day may not be far off. Artificial legs, unlike human legs, can be improved through engineering, and the companies that make them are hard at work on it. The model used by Pistorius is "a custom foot for track and field sports" with "optimal" sprinting ability, "superior functionality," and an "efficient energy return," according to the manufacturer's Web site. Other models promise "enhanced forward propulsion," "maximum performance," and "the highest energy storage and return capability on the market."

And that's just the beginning. The company's "bionic" site describes its work on "power motion," "neurosensing," and "artificial intelligence." Its introductory video declares, "The destination is life without limitations."

Well, maybe one limitation: You won't be allowed to run in the Olympics with your neurosensing, AI-controlled bionic legs. You'll have to run in the Paralympics with all the other superhuman athletes. It's only fair.

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