Wednesday, May 21, 2008

Amputee Gets a Shot at the Olympics

Continued from page 1

By Brittany Sauser

TR: Then how did the IAAF quantify the anaerobic energy source in order to come to such a conclusion?

HH: They took blood lactate measures. But again, if one is schooled in the recent scientific understanding of anaerobic metabolism, one concludes that by simply taking blood lactate measures, one cannot quantify anaerobic capacity.

At slower running speeds, the aerobic component can be measured by monitoring how much oxygen a person consumes and how much carbon dioxide is released. What we did is, we performed an energetic test at slower running speeds where one can quantitatively measure the total amount of energy required to run, because at that critical speed and below, the aerobic energy supply forms the entirety of the energy source. We measured Oscar and other elite athletes with intact legs at that speed and below, and we found no significant difference.

If the IAAF would have had their study peer-reviewed before deciding to ban Oscar, they would have found this out.

TR: In the second claim, the IAAF said that the Cheetah prosthetics returned more energy than the human ankle-foot joint. How was that evaluated, and why do you believe the ruling is flawed?

HH: The IAAF looked at the net mechanical energy of the human ankle-foot joint at 400-meter-race speeds and found that the ankle absorbs more mechanical energy than it releases. That is fine--they used standard procedure to look at ankle torque and power--but they then concluded that the body dissipates that energy. There is so much energy that is absorbed, and so much that is released, and they assumed the difference the body just throws out as heat. That is a highly questionable theory because typically the body does not throw out enormous amounts of energy as heat unless a person is continually going down hill where the body must dissipate energy. What might be an alterative hypothesis . . . is that not all of the energy is lost, and some of it is transferred to the knee. In our body, we have muscles that span multiple joints; for example, the calf muscle . . . goes past the ankle and the knee. Biomechanically, we know that one purpose of such muscles is so that the body can transfer energy across joints. The IAAF did not explore this possibility, but instead put forth a theory that the body is throwing all that energy out. They stated as fact that the human intact leg has a disadvantage compared to the Cheetah prosthesis, which is a spring, because it absorbed more energy than [it] released, and the difference is dissipated as heat.

TR: If the IAAF had assumed that the absorbed energy was transferred instead of dissipated as heat, would the energy measurements between the ankle-foot joint and the prosthetic have been similar?

HH: In terms of how much energy would be stored, yes. This also assumes that their very premise is valid, and their premise is that whether the ankle absorbs more than it releases or releases more than it absorbs at those speeds is the critical determinant of who wins the 400 meter race, which is highly suspect.

Peter Weyand [a member of Herr's research team and the director of the Locomotion Laboratory at Rice University] studies sprinting and what determines peak running speed, and he found that really fast people generate very high forces on the ground, and they do so very fast. Slower people are not able to generate high forces. One important feature of running fast is not what the joints are doing but the overall leg ability to generate high forces on the ground for a very short time. Now, we found that, and Dr. Brüggemann found that Oscar's ground forces seem to be slightly lower than an athlete's with legs. This suggests that perhaps he might be force limited because his prosthesis is just a spring, and he cannot generate the high forces an intact leg can.