Prosthetic Legs Aren't Better Than the Real Thing… Yet

By Andrew Moseman | November 9, 2009 2:55 pm

pistoriusSouth African sprinter Oscar Pistorius raised a ruckus last summer when the he wanted to qualify for the Beijing Olympics, thanks to the J-shaped carbon fiber blades that the double-amputee uses to run. Pistorius didn’t get to run in last summer’s games, but now an MIT team has released a study declaring that he doesn’t have an unfair advantage. Rather, the researchers found quite the opposite: Running blades for amputees, even made with today’s best materials, can’t compete with the legs that humans have evolved.

Pistorius has long argued that he should be allowed to compete alongside able-bodied athletes in races, but athletics authorities banned him from doing so in last year’s Olympic games, claiming that his blades gave him an unfair advantage over able-bodied athletes [The Guardian]. The MIT Media lab team led by Alena Grabowski helped to reverse his racing ban before turning its attention this year to the general question of whether blades or legs are better.

The team concocted a clever solution to the problem of testing this question. The study participants were six elite sprinters who had one intact leg and one leg that had been amputated below the knee. Researchers decided to study these types of amputees because they could compare their affected leg to their unaffected leg [Los Angeles Times].

Biology won the day, according to the results published in Biology Letters. The ground force a runner can exert—that is, how hard his or her leg strikes the ground—determines top speed, the MIT scientists say. And the sprinting subjects’ prosthetic legs supplied 9 percent less force on average than their biological legs.

While biology gets the better of biomechatronics for now, the researchers note a caveat: Their study compares today’s best prostheses to our biological legs, and prosthesis performance will probably improve in the future at a faster rate than the speed at which humans evolve better legs.

Related Content:
80beats: Toddler Gets a Telescoping, Prosthetic Arm Bone That Grows With Him
Science Not Fiction: Dr. Terminator: The Prosthetics Designer Who Makes Sci-Fi Sculptures
DISCOVER: High Powered Prosthetics: a bionic muscle 100 times stronger than yours

Image: flickr/Elvar Freyr

CATEGORIZED UNDER: Technology
  • bigjohn756

    It would be so much better if God would just heal these amputees, just like he heals all the other sick people.

  • Rillam

    What?

  • Brandon

    Thats weird, you must be mistaken this planet with another one; we call them “doctors” here, and a bonus the’re male and female too, twice the healing power; which will probably lead to limb regeneration/transplant, medical discovery in the future. Yaaaay!

  • YouRang

    Surely range of motion also contributes to top speed. So the curved shape of the prosthetic limbs is what is troubling. The force might be adversely affected, but if the prosthesis can maintain contact longer, even though the maximal force generated is less, the stored energy might offset the effect and the net effect might be greater.

  • TheCritic

    1. Bigjohn was probably referring to the site called “God Hates Amputees” which talks about all the miracles evangelists do on like people in wheelchairs, but no amputees are healed.

    2. Surely, yourang, surely your well-proposed theory has not been considered by scientists, none of whom would be well-versed in physics due to the fact that they’re scientists.

  • http://Information.Architecture.Abacurial.com tOM Trottier

    Power may be reduced by 9%, but the weight that must be propelled is also reduced because artificial springy carbon fibre limbs are much lighter.

    The study compared legs of single amputees. Having a fixed human leg also constrains the artificial limb in length and in rebound speed so that the runner can run synchronized. With 2 artificial legs, the length and rebound speed can be optimised for the runner without the constraint of having to match a human leg.

    The abstract says “force” but it is not clear whether this is a peak force, or a measure of the total power applied during ground contact. IOW, as YouRang indicates, if a lesser “force” is exerted for a longer time, due to greater artificial leg springiness, the total power applied may be higher. The actual paper presumably would clear up this ambiguity.

    The abstract also says, “Some elite unilateral trans-tibial amputee sprinters appear to have learned or trained to compensate for AL force impairment by swinging both legs rapidly. ” Bilateral amputees, ie with both legs replaced, may be able to swing their legs even more rapidly since the legs are much lighter. Lance Armstrong was noted for his high cadence compared with other elite cyclists. A higher cadence uses more energy, but can apply more power for a given maximum muscle strength.

    tOM

  • Bionic Kommando

    None of you people who take things for granted know what you are talking about and you know why? You are not an amputee. I lost my left leg below the knee in a motorcycle accident so I would say I have experience with what its like not having two real legs anymore. Your biological legs are something that can’t be matched by engineers….yet. Trust me, I could do so much more faster and better with my two real legs than I can now. Climbing things, running, jumping, standing all day, hiking etc. As far as regeneration goes, I have no doubt that they can do that already but the thing is that type of tech isn’t intended for us commoners. Only the richest and elitist will have access to that type of medical science. All I can say is this, if you are an amputee and you tell yourself and others people that you are happy with the situation then you are just lying to yourself. Everyday you know you wake up with regrets about your situation and sour feelings about what happened to you and how it affects your life.

  • Tbrad

    I would have thought that top speed determines the foot’s impact on the ground and not vice versa, but hey, I don’t work at MIT either, so.

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