Amputee Gets a Shot at the Olympics
Hugh Herr explains the scientific evidence behind the decision.
Last week, Oscar Pistorius, a South African Paralympics runner, was granted the chance to fulfill his lifelong dream of competing in the Olympics by the Court of Arbitration for Sports (CAS), in Lausanne, Switzerland. The court upheld the appeal filed by Pistorius against the decision made on January 14 by the International Association of Athletics Federations (IAAF) that banned the “blade runner” from competing against able-bodied athletes. The CAS ruled that the IAAF did not provide “sufficient evidence of any metabolic advantage … [or sufficient evidence] that the biomechanical effects of using this particular prosthetic device gives Oscar Pistorius an advantage over other athletes not using the device.”
Pistorius is a double amputee who competes on J-shaped, carbon-fiber, Cheetah Flex-Foot prosthetics made by the Icelandic company Össur. After Pistorius performed well in an international able-bodied event in 2007, suspicion arose among members of the IAAF that his Cheetah prosthetics may give him an unfair advantage. Immediately, the institution placed a ban on using “technical devices,” such as wheels and springs, in competition, and it decided to individually review Pistorius’s case.
The IAAF conducted a two-day scientific study, led by German professor Gert-Peter Brüggemann, of the prostheses. Based on the resulting data, the IAAF concluded that Pistorius indeed has an unfair advantage over able-bodied athletes, claiming that he uses 25 percent less energy than they do to compete.
Astounded by such allegations, Pistorius’s lawyers turned to MIT professor Hugh Herr and asked that he assess the scientific validity of the IAAF’s study. Herr, the director of the Biomechatronics Group in the MIT Media Lab, and also an associate professor in the MIT-Harvard Division of Health Sciences and Technology, assembled a team that included experts in biomechanics and physiology from six universities to evaluate the scientific evidence.
Technology Review sat down with Herr and asked him to explain the scientific flaws that the team of researchers found in the IAAF study, as well as the broader implications of the CAS’s ruling.
Technology Review: What were the claims made by the IAAF in its scientific report that you were tasked with assessing?
Hugh Herr: The first claim made by the IAAF was related to the metabolic energy required of Oscar to run. They claimed that Oscar, because of his Cheetah prostheses, was able to run at sprinting speeds with 25 percent less energy. In the second claim, the IAAF said the Cheetah prostheses release a greater amount of energy than the human ankle-foot complex in sprint speeds, and that that, in fact, introduces an artificial advantage to Oscar.
TR: In regards to the first claim, how did the IAAF come to that conclusion, and what scientific evidence did you use to refute that claim?
HH: At sprinting speeds, the body uses two sources of energy: aerobic and anaerobic. The problem is that you can measure one energy source but not the other. Anaerobic energy cannot be quantified by anyone–not here in the U.S., not in Germany; it simply can’t be precisely quantified. The IAAF claimed that it could be quantified, and they put a precise number on it: 25 percent energetic advantage at 400-meter-race speeds. This is deeply flawed because it can’t be quantified at those speeds. No one can assess quantitatively whether there is an advantage or disadvantage.
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.
Now, what our research is saying is not that [the IAAF study’s] data are flawed, but that it is the interpretation of the data we found questionable. The burden of proof is with the IAAF. If they want to ban Oscar and perhaps all amputees that use Cheetah prostheses, they need to show scientifically that it does show an overall advantage in the 400 meter race. Our point is that this is an important matter, and one needs to be very careful with the science. Therefore, there needs to be a high level of certainty of what biomechanically and energetically is going on in terms of the prosthetic effect. Brüggemann did a select set of experiments, and with that data, he did make certain scientific claims that we don’t agree with. We don’t agree with this interpretation of the data, but then beyond that, the IAAF made a much broader statement. They said that Pistorius has an overall advantage in the 400 meter race.
TR: Did your research team conduct any further studies to show either that the IAAF’s scientific evaluation was flawed or that Pistorius does not have an advantage?
HH: We did one measure that was not directly related to the claims made by the IAAF. If you take a sprint athlete, and at a particular running speed you measure the time duration they can maintain that speed, and then you change the speed and measure the new time duration and so on, you get a speed-duration curve. At really, really fast speeds, the person can take, like, 10 steps and maintain that speed for a short duration. As you lower the speed, the duration gets longer and longer. Sprint athletes with intact limbs all fall on a very standard line. We thought if Oscar is artificially augmented, he would not fall on that speed-duration curve. We did the test, and he falls right on the curve, which is an indication that he fatigues in the same manner as able-bodied sprinters.
TR: What are the broader implications of the CAS ruling?
HH: Oscar will be given the opportunity to qualify for IAAF-sanctioned events. But broadly, it will be progress in the overall initiative to fully integrate people with disabilities in society. Some people in the world witness an extraordinary athlete that has artificial legs or arms … and they immediately think that cannot be so–disabled people cannot be this good at something. It never occurs to some people that Oscar may be a remarkable athlete. They think he has to be cheating.
There is so much to learn about how the human body works and, in addition, how the body is affected by a wearable device, like a shoe or prosthesis. The day that there is a prosthesis that outperforms an intact limb using any single metric–whether it is to jump high or to manipulate something–will indeed be a very exciting day.