Oscar Pistorius - Science and Engineering vs Training. An evaluation of ALL the evidence

Welcome to the Science of Sport. If you are looking for the VERY LATEST discussion about the research on Oscar Pistorius' advantages ahead of the Daegu World Champs,  please read THESE ARTICLES:

1. The first study - the IAAF find "bouncing locomotion at lower metabolic cost"
2. The second study - how Herr selectively ignored data to make Pistorius look more similar when the evidence said massive differences and advantages existed
3. The mechanical advantages that explain why Pistorius has a running advantage

The article below was written in 2007, but has been "dated" by the latest publications by Weyand and further debate on the issue.

Thanks for visiting!

Ross

Evaluation of Science of Oscar Pistorius

So over the last month or so, we've had quite a big response to some articles written about Paralympic sprinter Oscar Pistorius. He is bidding to be allowed to run in the Beijing Olympics in 2008 for able-bodied athletes. We've carried a series of articles looking at the scientific merits of the case - there is a possibility that the Cheetah prosthetic limb gives him an advantage, and we wanted to look at the possible basis for this.

So last night, I was interviewed on an SABC show on the topic. It wasn't too bad, but I certainly felt that not all the cards were laid on the table. My perception of the media and this story so far is that it is actively being moved away from the science at every opportunity. And so hostile and aggressive responses are initiated every time anyone suggests that it may in fact be unfair to allow Pistorius to run. So what I realised last night is that no one is talking here. Science is saying one thing, but Pistorius is not directly addressing these concerns. Instead, he is actively engaging in a "smokescreens and mirrors" campaign to move the focus away from the science and onto the human element (which, by the way, is remarkable, no argument there). So what I then realised is that NO ONE has yet attempted to evaluate the evidence, both from the IAAF side and from the Pistorius side. So below is my attempt at this - it's a long article, I must warn you, but I do think it's complete and these points need to be heard. Thanks for reading!

The following four key issues are what I would consider important to the argument on Oscar Pistorius’ desire to compete in the Olympic Games in 2008. I really do believe that each is critical to the argument and would respectfully suggest that no article is complete without sufficiently mentioning each one.

1. Incentive clarification


Before even beginning to discuss the science of running on the prosthetic limbs, you have to clarify people’s incentives. It is critical that anyone who expresses an “educated” or scientifically formulated opinion on the limbs and their possible performance enhancing effects or lack thereof is understood in terms of their interests in the affair.  We must remember that science and commerce/business are very uneasy bedfellows, and so the incentive gap between the search for truth and the desire for an outcome (in this case, competition in the Olympics) must be acknowledged as a key driver of how we interpret information that we have at our disposal.

If anyone says that the limbs “definitely do not improve performance”, or confidently asserts that they are passive is lying. And what you will find is that this person has a reason, usually financial, to say so. Thus, the coach, the athlete, the sponsors, and anyone else with a vested interest in Pistorius must first clarify their position before expressing their “scientific” opinion. Again, science and commerce are uneasy bedfellows, and the perverse incentive created by the commercial pull is a bias that must be acknowledged.

2. The role of the IAAF


The IAAF, as the custodian of world athletics, must be cautious in how it approaches this particular situation. It is in a very difficult situation, but I must stress that I don’t believe that it will make a decision that is based on discrimination or bias in any way. We must try to return to the root question, and the issue here is not the discrimination of the IAAF vs. one person.

An unfortunate development over the last few weeks has been what I can only describe as a very hostile and aggressive response to the IAAF (and to me) by those supporting the bid to run at the Olympics. I read recently that Pistorius had labelled the IAAF as “pathetic” and “discriminatory” and suggested that they “wake up”. These statements are inflammatory, and I would hope and encourage the whole group, from both sides, in fact, to avoid such personal inflammatory statements. I have actually taken heat in the last few weeks as well, and for no reason other than people are interpreting this situation as personal and discriminatory, when it is not. The only issue is the credibility of the sport.

One has to realise that the IAAF must act now based on the possibility that in the future, the introduction of technology into the sport will be impossible to control. The possible implications of the technology are discussed below in Section 4, but briefly, the IAAF risk opening Pandora’s Box of technology in sport unless it can first be shown that the limbs do not confer an advantage to performance.

3. Evaluation of the scientific arguments


There are perhaps three key arguments for why the limbs would provide an advantage. What I will do is summarize each of these three arguments below, and this will be followed by my response to the arguments that have thus far been put forward by Oscar Pistorius and his team. I feel that it is critical to the issue that we discuss these theoretical concerns. To date, not a single one of the three main points I raise has been addressed by anyone. Rather, they are simply avoided and the focus is deliberately moved away from the science. So what I propose to do in the following pages is the first complete discussion and debate of the issues – I will first present why I believe the limbs confer an advantage and will then evaluate the counter-arguments, according to Pistorius.

Key scientific argument 1


Spring design of the legs and implications for running


Firstly, there is the issue of the design of the limbs – the limb is specifically designed to store and then return as much energy as possible. In fact, if you go to the Ossur website (Ossur is the company which manufactures the limbs), you will see statements to this end. I quote verbatim one such statement below:

“Vertical forces generated at heel contact are stored and translated into a linear motion described as Active Tibial Progression, from the foot-flat to toe-off phase. This action reduces the need to actively push the body forward using the contralateral foot as well as equalizing stride length”
This statement is effectively saying that the prosthetic limb is able to take the forces that are generated DURING LANDING, store them and then translate this into FORWARD movement. In effect, the limb is able to propel the athlete forward. Now, a human limb is similar in respect to being able to store energy. However, there are two critical differences between the human limb and the Cheetah Prosthesis.

1. Firstly, the human limb is unable to translate the energy into FORWARD MOTION. The Cheetahs, I gather can do this because they have their unique shape. A human limb cannot take a force in one direction and convert it to another without requiring muscle contraction.
   
2. The human limb is not able to return energy PASSIVELY. In otherwords, if you jump off a box and land on the floor, you do not bounce up, and almost all the energy that might have been stored is lost. This means that if you want to use that energy, a human limb must ACTIVELY contract. There are many studies that have shown that if a landing phase is followed by an active contraction, then at most 70% of the energy can be recovered. Some studies have found energy return of only 30%, much less than the Cheetahs, and this is ACTIVE return. The point is that this recovery of energy is ACTIVE – it requires muscle contraction and therefore requires energy. Pistorius does not require energy, and so the metabolic cost of running will be lower and he has a potentially enormous advantage as a result.

The implication of this physiological reality is that the energy cost of running may be reduced. During running, it is factors related to metabolism that are responsible for the fatigue experienced by athletes. These, and the oxygen demand from the muscles, will be reduced in Oscar Pistorius. This is, until proven otherwise, a clear advantage.

Key scientific argument 2


Reduced limb mass


At its core, sprinting is about accelerating mass. In otherwords, the athlete uses muscle, which applies force to a mass to cause it to accelerate. It is well known in coaching and in science, that two factors can influence how much acceleration can be achieved. The first is the force that is applied by the muscles. This is the reason that the sprinters you see on television are so extremely well-built and defined – a great deal of power is required to sprint.

The second factor is mass. A smaller mass is easier to accelerate. Now an athlete’s lower limb would usually weight between 5 and 8 kg. In Pistorius’ case, the limb is massively reduced by ultralight carbon fiber blades that weigh no more than 1kg. This means that he is saving approximately 6 kg on each leg when he runs. I would challenge anyone to go out and run with an extra 6 kg tied to each leg and see how far they get. The reduction in mass is thus a massive advantage.

Now, the counter-argument to this is that Oscar does not have calf muscles to assist with this force generation. This is of course true, and so the scientific response is to look at just HOW MUCH DO CALF MUSCLES ACTUALLY CONTRIBUTE TO PROPULSION DURING RUNNING? And the answer is surprisingly little. In fact, studies have estimated that during walking, only 6% of the total energy comes from the Achilles tendon and calf, and during hopping, it rises to about 16%. Therefore, for sprinting, we might assume it is between 10 and 15%. This is a remarkably small amount, when you consider that the reduction in mass is probably 90%. So he is losing maybe 15% of his ability to push forward, but he also loses 90% of the weight of the lower limb, and about 40% of the total weight of the limb.

In Pistorius’ case, then, the main muscles that are working during running are the hip flexors – these are the muscles that drive the knee forward. These muscles are without any doubt doing less work considering the greatly reduced mass that they are responsible for accelerating.

Key scientific argument 3

Stride length and frequency


In the initial stages of the bid to be allowed to compete, one of the key factors put forward by the IAAF and myself were the possibility that the prosthetic limbs would provide a longer stride than for an able-bodied athlete of the same height. There are two reasons why this might be so:

1. The spring effect of the limbs, which was discussed previously. I have already commented on this, and the fact remains that the limbs are designed specifically to PASSIVELY return energy to the runner. An able-bodied athlete must ACTIVELY contract the muscle to capture and use this energy.
   
2. The fact that the prosthetics are designed to simulate the ability of the runner to run on his toes. In sprinting, runners usually land on the ball of the foot, but the problem is that the ankle, which is a hinge joint, “Collapses” and causes a great deal of inefficiency. If the ankle could be locked in place, it would increase stride length and mechanical efficiency substantially. Now Pistorius has this advantage automatically. This is, in fact, the reason that he is able to beat the single-leg amputees so easily – they have to have one leg shorter than the other, because otherwise, their natural leg would collapse every stride, the prosthetic would not, and they would rock from one side to the other substantially more than an athlete does anyway.

Therefore, the opportunity to design a limb that maximizes stride length is a potential advantage. I am not suggesting that he has longer legs than he would otherwise have had. However, the fact that he is pushed onto the “ball of the foot” artificially increases the stride length and efficiency, providing an advantage.

Evaluation of the counter-arguments. What claims are made by Pistorius?

Having described the evidence that I believe is suggestive of an advantage, we now need to consider the opposing view, namely that the legs do not confer an advantage. These opposing views are drawn from articles published on the internet and in newspapers in the last 3 months.

Scientific rebuttal 1 – the limbs are less efficient than a human limb


The claim has been made that the Cheetahs are in fact less efficient than a normal human limb. A scientist has made the claim that the human Achilles Tendon is able to release 240% of the energy it stores. This claim is patently incorrect – I have quoted studies that have shown that the Achilles tendon can only return between 30% and 75% of the energy it stores. Further, the human calf and tendon cannot take force in one direction and convert it to another – the prosthetic limb can do this, as I explained. Finally, and this is also explained in detail above, the human limb does not return most of the energy passively – it requires active muscle contraction. The assertion then, that a human limb is more efficient is not correct. My feeling is that these claims are made by scientists who will say whatever is required as soon as the price is right.

Scientific rebuttal 2 – Oscar has as much lactic acid as other runners


In a recently published article in the Sunday Independent, Pistorius made the following claim in response to issues about the metabolic cost of running:

Obviously I don't have a build-up of lactic acid in the legs, but I have the same ratio of blood per muscles in my body as everyone else, and the only way you'd get less lactic acid would be if that ratio was less. The IAAF haven't spoken to me and they haven't spoken to my physios, who work on my back every day because it's screwed up with so much lactic acid in it. I have to ice my back every day so I can train the next day because of the lactic acid build-up.

Firstly, it must be pointed out that lactic acid is not responsible for his back pain to begin with – lactic acid is gone from the body within the first 30 minutes after stopping exercise, and so back pain felt even one hour later is NOT caused by lactic acid. This is a theory that exercise science has debunked in the last ten years, and is thus out-dated.

Now, the next consideration relates back to the two points I raised previously. Firstly, the fact that the Cheetahs return energy passively rather than actively means that the metabolic cost of running is reduced. Second, the main muscles of locomotion are doing less work to accelerate a lighter mass during sprinting with Cheetahs. As a result, the reason for the lower lactic acid levels is not the ratio of blood to muscle to begin with – it’s the work being done by the muscle that is reduced. The base assumption is thus incorrect.

Scientific rebuttal 3 – Oscar is the only athlete to run these times on the limbs, so it must be him, and not the technology


This particular argument has been made on numerous occasions. The claim, essentially, is that the limbs have been around for 14 years, but no one has run these times, so it must be Pistorius who is responsible and not the limbs.

First of all, the Cheetahs were only developed in 1996, and Ossur bought the design in 2000, so the feet as we see them today are only about 6 years old. Of course, prosthetic limbs have been around longer, but if the whole argument is that technology is advancing, then old technology is not valid. In fact, if you think about it, this whole “best athlete in history” claim actually supports the theory that the legs improve performance – if it was natural athletic ability, then it is more likely that someone in the last twenty years would have been close to these performance times. 

Instead we have a situation where an athlete is only emerging now, which happens to co-incide with what is arguably the biggest boom in technology that the world has ever known – we are in the age of technology. The company Ossur is now making limbs with intelligent, electronic knees, which improve stability massively. It does not seem to me to be too big a jump to assume that limbs are improving at the same time. So the claim that the SAME LIMBS have been around for 14 years is patently incorrect. Further, Pistorius’ own coach, father and himself have been quoted in the media talking about how they were able to run faster when they received new limbs. So it is the growth of technology that may explain why Pistorius is the only runner to run these times.

Remember, I explained earlier why a single-leg amputee will never be able to run these times – they are unbalanced. So the point is that Pistorius, as a double amputee is advantaged against single-leg amputees. The next question is what about double amputees? Why are there no other double amputees? The reason is relatively simple – it requires an absolutely remarkable series of events to produce a double-amputee who is also athletic. The following factors must all come together to produce a double-amputee athlete:

1. The athlete must be born without legs, they cannot lose them after they have started walking or have learned to walk. It is almost impossible to “relearn” the motor control patterns that would be needed to run and sprint again
   
2. The athlete must be wealthy. Even basic prosthetic limbs are too costly for a lot of amputees to afford. As a result, the vast majority of potential runners cannot afford to compete on an even-playing field. The beauty of athletics is that it allows all athletes, regardless of income and wealth, to compete. This is why the Kenyans, who may be impoverished, can race equally against Chinese, Australian, Swedish and American runners. In the category of double amputees, this is impossible. I am informed that the Cheetahs cost about $18 000 EACH. Few athletes can afford this.
   
3. The athlete must have physical therapy from a young age. Learning to walk on prosthetics is a huge advantage, and so too is the therapy from a young age, which enables the person to function relatively normally and gain the necessary balance to perform sporting activities. This is not available to all children who have amputations.

A final consideration is that the amputation must be below the knee, because the loss of the knee joint and the stability and power it provides would be impossible to overcome. Needless to say, Pistorius received all four of these essential requirements. And while his achievement is no less remarkable, he finds himself in the ONLY possible situation to be able to run – it is a very small percentage of people who fall in this category to begin with. This, combined with the advances of technology are the explanations why we are seeing this situation now.

Acknowledged disadvantages


At this stage, it is important to identify the single factor that is without doubt a disadvantage to Pistorius. And here, I have no hesitation in saying that Pistorius is at a disadvantage and that is from the starting blocks. Because of the double amputation, and the fact that Pistorius is running on legs that have a very small contact area with the ground, his balance from the blocks is compromised. It is for this reason that he starts so slowly and then has to catch up distance on his rivals. However, in the 400 m event this disadvantage is greatly reduced, and is almost minimized, and that is the reason why I suggested in an interview after the 2004 Athens Paralympics that he should consider stepping up to the 400 m event. 

I’m sure that this was the plan anyway, but it made sense, because the start in the 100 m and 200 m events are so crucial. In the 400 m event, this is less important and the result is that his disadvantage is reduced. I dare say that the 800 m event is even more likely to be a strong one, particularly since the metabolic theory seems so obviously correct – no peripheral metabolites regulating performance will result in a massive advantage, perhaps even greater than in the 400 m – you read it here first!

So an objective analysis of the situation tells us that he has this disadvantage, which is partially offset by the fact that he is now running in the longer 400 m event

The implications of technology in athletics – the role of the IAAF


I think that it is critical for people to realise that the IAAF, as custodian of the sport, must make a decision that stands up to scrutiny in ten years’ time. Therefore, it must be emphasized that this is not an issue about IAAF vs Pistorius, or about Tucker vs Pistorius. At the heart of the issue is the introduction of technology to the sport, and the future consequences of this decision. I would appeal to everyone to try to consider the situation from the perspective of the IAAF. It is not a question of fear or embarrassment that a Paralympic athlete can compete with the able-bodied athletes. They are not “scared” of the reality. Their concern is how their decision now will impact on the future of the sport, regarding technology.

And the key here is that technology makes it very difficult to regulate how improvements in sport are achieved. This is analogous to the situation in F1, where advances in technology made cars faster and faster, until the point was reached where driver skill was becoming increasingly minor to the performance of a car. Now, in athletics, we may be faced with a situation where a 0.5 second improvement can be achieved through the slight manipulation of equipment, and this is not acceptable, since it means that training is difficult to quantify.

In fact, there is little evidence that over the last 3 years, Pistorius’ improvements in the 400 m event have been the result of anything other than technological advancements – articles on the matter have mentioned how Ossur and Pistorius have worked together over the last few years to improve on the technology. In a letter to a website, Pistorius’ prosthetist has described how they have to align the limbs for best results, how they have to set them correctly, ensure that they are strong enough, manipulate the elasticity, work on the aerodynamics etc. This to me suggests very clearly that what happens OFF THE TRACK, in terms of the engineering and preparation, plays a vital role in the on-track performance. 

Now, we have a situation where an athlete has improved and we cannot account for the ORIGINS of this improvement. Was it due to training? Or was it due to improved aerodynamics? The mere fact that the athlete and the scientific and engineering team work so closely to develop prototypes is an indication that the limb design does play a role in performance and that’s not a situation that the IAAF can afford to create. We are in danger of opening Pandora’s Box and introducing a new realm of performance enhancers to the sport.

All of this invites the obvious study that needs to be done. I would anticipate that many people, notably those who are pro-Pistorius, will be claiming that aerodynamic advantages and technological advantages are there for all to benefit from. So what I would suggest is that Pistorius must run in limbs that were used in the 1996 Paralympic Games. And Jeremy Wariner must run in shoes and clothing that were worn in the 1996 Olympic Games (both in Atlanta). And then we will immediately see whether the change in technology affects one athlete more than the other. My suspicion is that Wariner will run almost exactly the same time in the shoes from 1996 as he can in the shoes from 2007. What will happen with Pistorius? Because if he can’t run the same time, then we have the answer – the improvements are technological.

And if the improvements are technological, then allowing him to run at the Olympic Games will present the whole world with an opportunity to benefit from the SAME technology. Because you cannot outlaw technology for some athletes, but not for others. And before you realise it, Nike, Adidas, Mizuno and Reebok will all be designing shoes that have the same spring properties as the Cheetahs. It will have opened Pandora’s Box, and my prediction is that a sub-40 second 400 m will be achieved within five years.

I was asked in a debate on TV last night whether I felt that Oscar Pistorius was a gifted athlete. I said, Yes, absolutely. And I meant this – there is no doubt that he is a very talented athlete. Most of all, his determination and courage have stood out as inspirational to a lot of people. But we have to realise that there are probably 10 000 people in the world who can run a 400 m race in 47 seconds. There are only 500 people who can run it in 45 seconds. Oscar is one of those – but whether it’s natural ability or technology that is responsible, that’s the question. And perhaps most telling of all is the following statement, which was made by a journalist who wrote a feature article on Oscar Pistorius for a magazine that is published and produced by Ossur. I emphasize that this article is biased in favour of Pistorius, since it’s written by the very people who make his Cheetahs and thus have a direct financial interest in him running in Beijing:

“To give me a sense of how they feel, Ossur’s engineers bolt a pair of Cheetahs to the back of two rigid plastic and leather motorcycle boots. I clamp in and trot across the room a few times. The Cheetahs seem to bounce of their own accord [emphasis added]. It’s impossible to stand still on them, and difficult to move slowly. Once they get going, Cheetahs are extremely difficult to control”
Does this sound like a passive device? Do human limbs bounce of their accord? Does it sound to you as though these Cheetahs do not play an active role in assisting bounce and movement? And of course, the big challenge is to control them. That’s not easy, and that’s what Pistorius does best. But then he learned to walk on them, it’s not that unusual. Gymnasts are able to balance on a 5cm wide beam because they practice for hours a day. I could not imagine being able to do that either. But it’s possible. And it’s possible that in five year’s time, if the IAAF let this through, that a 26-year old American sprinter will run the 400 m event in 39.5 seconds, because the “shoes” he wears make it “difficult to move slowly” and “bounce of their own accord”.

Ross

See also An Open Letter to the IAAF on Oscar Pistorius, published 2 July