September 2009

Out on a limb: Getting a leg up

Jordana Second Headshot LERby Jordana Bieze Foster, Editor

So now we know more about Oscar Pistorius’ body than any of us does about our own. Courtesy of the Journal of Applied Physiology and a dream team of scientists, we know his metabolic cost of running, his sprinting endurance, his swing times, his stance-average vertical ground reaction forces. We know how each of those variables stacks up against those of elite non-amputee runners.

But we still don’t know whether his prosthetic feet give the Paralympic superstar and bilateral transtibial amputee a competitive advantage. Or what it would mean if they did.

The research published in JAP confirmed that Pistorius’ running mechanics are significantly different from those of runners with intact limbs, and that his physiology is similar. In other words, the differences in his mechanics don’t make his running any more efficient, at least not in terms of the specific variables tested. Those findings created enough reasonable doubt to overturn the International Association of Athletics Federations ban of Pistorius from its events (although he failed to qualify for the 2008 South African Olympic team). But the study’s authors deliberately avoided going on record with any written conclusions as to the superiority of running on either prosthetic or biological limbs.

Subsequent studies comparing the prosthetic and intact limbs of elite unilateral amputee runners have further explored the mechanical differences (see “Amputee runners hit the lab”), and it seems clear that present-day prosthetic limbs come with at least one disadvantage for runners—their inability to stiffen at high speeds, as biological limbs do, ultimately limit amputees’ ability to generate velocity by hitting the ground with more force.

Perhaps ironically, this research just might be a catalyst for the development—someday—of prosthetic technology that actually does outperform biological limbs. But even that wouldn’t have to keep Pistorius and others out of the Olympics.

The IAAF does grant therapeutic use exemptions (TUEs) to athletes who take otherwise banned pharmaceutical products for medical purposes, on the condition that the substance “produce no additional enhancement of performance.” If researchers could determine the technical specifications for which a prosthetic foot was equivalent but not superior to a biological limb, verifying those settings prior to a race would be a heck of a lot easier than drug testing.

But really, if amputees had the ability to run faster than non-amputees, they might be better off without the IAAF and all of its rules. Given the worldwide popularity of auto racing, there might well be a significant number of speed-needy fans who would prefer to see these athletes test the limits of what prosthetic technology could really do.

Granted, most amputees are not would-be Olympians, and most lower extremity practitioners have patients with much more modest activity goals. So what does all of this mean for you and your patients? Just this: When prosthetic technology reaches the point where it actually does give elite athletes a competitive advantage, the current clinical challenge of providing the average amputee with a normal gait shouldn’t be much of a challenge at all.

When that happens, you can thank Oscar Pistorius. If you can catch him.

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