By Dr. Ross Tucker
The selection of Oscar Pistorius to the South African Olympic team is bound to re-ignite the debate around his eligibility to run against able-bodied athletes, with world-record holder Michael Johnson most recently stating his view that Pistorius should not compete in able-bodied races until it is conclusively known whether the prosthetic blades provide a performance advantage.
This issue, which has been in the media since 2007, is one of the most emotive sporting controversies in the world. I have recently been contacted for opinion on what is a complex debate, and rather than provide fragmented and isolated views, I have put together this statement as concise an explanation as I believe is possible in this debate, to summarize the scientific issues at hand.
Further, Pistorius recently labeled the scientific arguments as “so weak”, and continued to label scientists like me as publicity hungry and ready to “sing a song” to make a name for ourselves. It’s unfortunate that personal matters come at the expense of scientific debate, because in using this ‘strategy’ of personal attacks, Pistorius never discusses or explains what “weak” arguments scientists like myself have put forward. Therefore, this statement serves to outline the important scientific issues.
To begin with, I must stress that there is no question that Pistorius inspires many, draws substantial interest to the sport, and has served as a role-model and example of courage and perseverance in the face of substantial challenges. This status should not be in question as a result of this debate.
However, there is also a scientific question at hand, and it asks whether Pistorius has an advantage as a result of the carbon-fiber prosthetic limbs, known as Cheetahs, that he sprints on? Removed from the emotion, this is a fascinating question, with a controversial answer.
The media coverage of Pistorius largely ignores this, and has focused exclusively on the unquestionable emotive qualities of the story, often in a rather fawning manner. This is of course the prerogative of the media, and it is valuable to discuss the emotional and inspirational qualities in this story. However, there is a parallel, scientific debate, perhaps larger than one man, which has been largely neglected. The reality is that the science on this issue now appears relatively simple, and it says that the advantage is real, and potentially large.
It may seem ludicrous to suggest that an athlete with no calf muscles has an advantage. Common sense would dictate that they are at a disadvantage. However, this is not a scientific debate that can be answered using common sense. Rather, we should use a scientific process and research data to answer it.
The process begins, as all science does, with a hypothesis based on known theory. In the case of Pistorius, an advantage would exist for three theoretical reasons:
1. The light mass of carbon fiber limbs means that the limb can be accelerated faster, which means faster limb movements and thus faster sprinting
2. The stiffness of carbon fiber returns more energy than human tendon, effectively functioning as an improved sprint compared to tendon and muscle
3. Carbon fiber does not fatigue like muscle and tendon do. Fatigue is a crucial factor in a 400m race, and so the absence of fatigue is a theoretical advantage
Given these three theories, one would make the following predictions about Pistorius:
1. His running mechanics will be completely different from able-bodied runners, because his leg movement will be much faster than it is in able-bodied runners. This will be a significant advantage because running speed is in part a function of how fast the legs move
2. He will use less energy than able-bodied runners, and this will be measurable through a lower than normal oxygen use at any given running speed. This is analogous to a car that uses less fuel to travel the same speed or distance, and is a performance advantage
3. He will show less fatigue over the course of a 400m race
All three of these predictions are advantageous to performance, and all three were tested on three separate occasions, first by the IAAF and then by a team of Pistorius’ own scientists. This is what was found:
1. Pistorius uses 25% less oxygen than able-bodied runners when sprinting. This suggests that he uses less energy, as predicted by the theory
2. Pistorius uses 17% less oxygen and energy than able-bodied sprinters at a range of running speeds. This confirms the theory that he runs the same speed with less “cost”
3. Pistorius’ carbon fiber blades return 92% of the energy they store when he lands. Think of them as springs, which bounce back with 92% of the energy every time. Human tendon and muscle is only able to return about 41% of their energy, and so carbon fiber is a better “spring” than human tendon. To put this simply, human legs lose about 59% of their energy with every landing, whereas carbon fiber Cheetahs lose 8%. That’s a seven-fold difference that gives an energy advantage
4. Pistorius is able to move his legs 21% faster than other sprinters, and 11% any sprinter ever measured, including Olympic 100m champions. This is vitally important, because research has shown that there is a lower limit to how fast able-bodied runners can move their legs. In other words, we are all limited by the speed of our leg movement. This limit does not exist in Pistorius – he is able to move his limbs faster than ever seen before, exactly as the theory predicts, and this means faster running with less energy cost
5. The result of moving his legs so fast is that Pistorius does not need to apply force to the ground in the same way that able-bodied runners do. If you think about running faster, you can do it in one of two ways – you either move your legs faster, or you apply more force every time you push off the ground. Able-bodied humans have a limit to how fast they can move their legs (see Point 3), and so they have to get faster by pushing harder against the ground, using more force. Pistorius does not. As a result, he is able to run at world-class speeds with less force, or less athletic effort, than able-bodied runners.
6. Pistorius does not slow down as much as able-bodied runners in the course of a 400m race. This suggests less fatigue, as the theory predicts.
These five findings, all in controlled scientific studies, prove exactly the theory for why Pistorius has an advantage. They confirm the hypotheses exactly. In a scientific process, then, the only conclusion that can be drawn is that the advantage does exist, and not a single piece of evidence has been produced to suggest that this is not a nett advantage.
In terms of potential disadvantages, the commonly raised one is that Pistorius does not have calf muscles, and so cannot push off the ground. There are two physiological responses to this argument. One is that the calf and Achilles tendon do not contribute much to forward propulsion – only about 6% of our forward movement during running comes from calf muscle contraction. The truth is the main function of the calf and Achilles is NOT muscle contraction, but rather to act as a spring. Therefore, the question we should be asking is which is a better spring, the calf/Achilles, or the carbon fiber prosthetics? As explained, carbon fiber prosthetic limbs have been proven to do this “spring” job more effectively than tendon and muscle.
Finally, it must be acknowledged that Pistorius was cleared to run by a Court in Switzerland, after an initial ban. The specific legal and scientific details of the process and decision are complex, but I would point out that much of the evidence discussed above was not presented at the hearing. In fact, it took 18 months for the evidence of a performance advantage to emerge, because this side of the science was kept quiet. The scientists who tested Pistorius were sidelined from the court hearing, and the only evidence that was presented was data that was selectively manipulated to show no advantage. The scientific process was highly questionable, and even the published research was skewed to portray an inaccurate picture, and the full scientific facts emerged eighteen months later.
Many have suggested that if it is true that carbon fiber prosthetics are better than human limbs, then people should amputate their legs to get access to the equipment. However, this is a false over-simplification, because one of the key requirements of the prosthetic limbs is the co-ordination and ability to use them, because balance is an important challenge. Pistorius, who learned to walk on prosthetic limbs, does not have this disadvantage, whereas any adult who has to relearn to walk and then run is unlikely to gain the skill necessary to run fast.
In this regard, Pistorius is highly skilled at using the equipment. It is equipment, however, which I am convinced gives a potentially large advantage, despite a recognized disadvantage of balance and propulsion, and the scientific evidence points towards this large advantage by confirming exactly all the theories for it.