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Monday, June 02, 2008

Pistorius myth busting

Oscar Pistorius, science and Ossur: Let's start by exposing some myths: The human tendon DOES NOT return 249% of its energy...

Yesterday I wrote that now that some of the science that was presented to the CAS is finally emerging into the public, we'd be taking a look at the other side of the argument, and applying the same kind of scrutiny to the science produced by Pistorius as he was able to apply to the IAAF testing results.

I've been reading up on that science in various interviews with the scientists who did it, and it's a source of both amusement and frustration to see how confident those scientists are in their own data. That is not a typical scientific approach, because scientists learn very quickly that no study is perfect or beyond question, particularly this one, though such knowledge would seem not to apply to those who did the research.

But then this morning, I received an email from a journalist (our maven, Jim!) which had an article written about Pistorius in which the technology was again discussed. And once again, I came across the following quote from that article:

"The Cheetah Flex-Foot uses carbon technology to store and release energy. It is known as a passive prosthetic foot - meaning it is limited to returning a portion of the energy stored during the loading phase of running.

The shape, which somewhat resembles the hind quarter of a Cheetah, acts like a spring and shock absorber. The “J” curve is compressed at impact, storing energy as well as absorbing high levels of stress that would otherwise be absorbed by the knee, hip, and lower back. The “J” then returns back to its original shape, releasing a percentage of the stored energy and propelling the user forward. Studies have shown the “J” curve can return around 90% of the load applied to it. In contrast, a normal able-bodied foot and ankle system can return 249%. "

That got me thinking about how many myths there in this whole debate, and I thought that before tackling the issue of energy and oxygen-use, I'd briefly address two of these myths.

Myth # 1: The energy return of the able-bodied leg

The able-bodied foot and ankle system CANNOT return 249% of the energy it stores. This theory, which I recall from last year, was put forward by a Professor Robert Gailey, of Miami.

Frankly, this kind of theory that should come out of Hollywood, not Miami, where the special effects gurus and techno-geniuses might make it happen. On planet earth, it's a complete fallacy. It violates every law of physics and thermodynamics, in that you cannot CREATE energy, which is what Gailey and the article are saying.

In effect, they are saying that the human ankle and foot system is able to take the energy when you land, and then passively return two and a half times as much energy. Imagine you climb onto the roof of your house and drop a basketball on the ground below you - if Gailey and Pistorius are to be believed, then the basketball, were it made of human tendon, would bounce up off the ground and reach a height two and a half times higher than where you are standing! After another 19 bounces, the basketball would be 91 million meters high! The beauty of "perpetual motion"...on steroids.

That happens in Hollywood, where actors like Robin Williams can invent green matter that bounces off walls and has a mind of its own - it was called "Flubber", if I remember correctly. But that kind of Hollywood science is best left out of this debate.

The truth, for those interested in it, is that the Cheetah Prosthetic releases between 80% and 90% of its energy, the human leg between 30% and 70%, depending on whether the person is walking, sprinting or hoppping. As for the 249%, I suspect that comes as a result of (deliberate) "confusion" around the fact that in humans, muscle contraction might increase the force output - but it's not free energy, and it's definitely not the "release" of energy that is being measured. The great irony in all this is that the whole defence was that the Cheetahs are "passive" - that's precisely the problem! Humans are not passive - muscle contraction has a cost, and that payment is the difference between Pistorius and able-bodied runners.

There are some other myths in the scientific case that will be discussed - but that's for next week, when we start to look at the results from the now famous "Houston" testing. First, another myth regarding the PR campaign launched around the issue.

Myth # 2: The "same" Cheetahs, or new ones?

The second myth is a little trickier, because it becomes a game of "he said, she said", where it's difficult to prove who is correct. But in effect, it revolves around whether the Cheetah blades used by Pistorius are the SAME as the ones that have been used for 14 years. This claim has been made often by Pistorius and most recently by Ossur, the manufacturer, and I suspect that many will argue this, despite the quotes shown below.

To get to the bottom of this, you have to either blindly believe what you are told, or read between the lines. And when you take the latter approach and start questioning these statements, then you start exposing the fraud.

Take for example, the following quotes, from a magazine called Wired. The journalist who writes the piece spends time with Pistorius in South Africa and in Iceland, where Ossur are based. He sees the equipment, gets to try on the blades, spend time getting to know the inner-workings of Ossur. Also, he has no obvious conflict of interests, no reason to propogate the lie, and so his opinion is more believable than that of Pistorius. He exposes (quite by accident) some of the lies put forward. For example:

"A company called Flex-Foot debuted the Cheetah in 1996, but the prosthetic blades remained a bit crude until Flex-Foot was acquired by the Icelandic firm Ossur in 2000. If you are missing a leg, owning an Ossur is like driving a BMW M-series.

The current Cheetahs look a little like the rear leg of a horse or cat, extending straight down from the socket, cantilevering backward, and then angling forward sharply. But last September, Pistorius and Brauckmann went to Reykjavik to test prototypes designed for double amputees. The new ones, which Pistorius hasn't debuted at a major race yet, make just one smooth curve, an arc of pure engineering."

So the first point is that the blades "were a bit crude" until 2000 - not 14 years ago. That's when Ossur joined the fray. Secondly, they are constantly working on new designs, and have one in the cupboard that hasn't been debuted yet, but is clearly an improvement on the current design (the CAS ruling does prohibit this from being used, incidentally. Though good luck to the IAAF in enforcing that). But if you don't believe the new age of the Cheetahs, here are two more quotes from the article:

"Since Athens, Pistorius has been running in Paralympic events, but also against able-bodied runners. After overhauling his training regimen and working with redesigned, customized prototype prosthetics, Pistorius is on pace to run the 200- and 400-meter sprints fast enough to earn a spot on South Africa’s Olympic team. He’d be the first amputee runner to cross over."

"It’s also true that the Cheetahs Pistorius hopes to run on in Beijing, with their pure-engineering swoop, are in quantifiable ways better — faster — than the ones he ran on in Athens."

That would suggest, then, that since 2004, Pistorius hasn't run on the "same" Cheetahs as they've been using for 14 years, but rather gets to test out customized, prototypes, perhaps every season. Again, the CAS ruling said that the decision applies only to the blades evaluated by the IAAF - well, good luck trying to enforce that when prototypes are flying around... it only cost the IAAF $80,000 to do the testing last time.

Bottom line - there's more to this than what the PR people and media have portrayed here, and that's the problem facing athletics today, thanks to the CAS and the "science" they evaluated. Speaking of that science, next time we revisit this particular topic, it will be to describe some of the science, and we'll begin by looking at the oxygen cost and energy use question. That will be done by next Monday, so join us then.

The scientists who represented Oscar Pistorius are convinced they've shown that his energy use is normal (at jogging speeds, mind you - hardly relevant for a 400m sprinter, you'd think). They clearly haven't considered three simple predictions their finding makes. Ironically, when you go step-by-step through their findings,and those three predictions, you're left with no choice but to realise that physiologically, the advantage exists. So the science proves the point, even when it's done from the other side.

Join us then.



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Anonymous said...

If you had done a little research, you would have found:

Gailey presents a layman's version of a scientific article by Czerniecki (1991).
here is a quote from the Gailey web article:
The "elastic energy" found in the anatomical foot has been replicated to varying degrees in prosthetic feet. Dynamic feet have been found to generate two to three times greater elastic energy than SACH feet. Czernieki, Gitter and Munro (1991), defined spring efficiency as "the amount of energy generated, divided by the amount of energy absorbed." The spring efficiency of the SACH foot was found to be 31 percent, the Seattle foot had 52 percent, and the Flex-Foot had an impressive 82 percent. In comparison, the human foot has 241 percent spring efficiency, with the addition of the concentric plantarflexion contraction.

Please note that the 241% includes the power produced by the plantarflexor muscles. It does not violate any thermodynamics principle. A passive spring (i.e. a Cheetah) can not produce more energy than is stored in it. A human leg with a muscle and tendon can produce more power than is stored in the tendon.

Gailey has a long career of helping people with amputations. You owe him an apology.

Ross Tucker and Jonathan Dugas said...

Hi Anonymous

Forgive my mirth, but I'm chuckling quietly to myself as I write this, because you've fallen perfectly into the trap set for you by the PR people, with whom Gailey was complicit in portaying the energy return in this way.

Your own words:

"Please note that the 241% includes the power produced by the plantarflexor muscles"

In that case, you can't refer to the 241% as energy RETURN - it's energy OUT. The addition of energy by the muscles means it's no longer return, but output. That seems a little significant to me...

You also refer earlier to a paper where it claims that energy GENERATION was part of the equation. OK great, I agree with that (never have I said that it's not true). But, here is what you missed - Gailey chose to portray the Cheetahs and human limbs the same way, yet conveniently ommitted to include that part of the energy return was muscle contraction.

Now, perhaps you might do some homework of your own and work out that the problem with energy GENERATION is that it comes at a cost. That is, energy production has a price, and that price is fatigue. Therefore, you are missing the most important thing of all - the Cheetahs allow energy return for free, and hence fatigue resistance is the upside.

But no, it was reported as energy return, Robert Gailey was quoted in this way, and whether it was deliberate or ignorant makes little difference to me - the truth was misconstrued, so no apology today I'm afraid.

Though you might consider re-reading that entire section, as well as the media reports, and then consider your own stance. May I remind you that this post is not a direct attack on anyone, though the science is completely taken out of context. This is an indictment on the media, who present scientific facts out of context.

Gailey may well have helped many people, but that's irrelevant to this debate. Just because you help people does not entitle you to immunity from facts...Lance Armstrong helped millions of people with cancer: Should we then not ask the difficult questions about drug use because of it? It seems to me that you would subscribe to that line of thought.

If you're looking for vindication through an apology, perhaps you should be writing your letter to the media. you'd still be wrong, but they might relent.


Anonymous said...


I would like to refer to anonymous and his excerpt from Gailey´s research.
"...In comparison, the human foot has 241 percent spring efficiency, with the addition of the concentric plantarflexion contraction".

When you are talking about efficency, then the maximum or the optimum to be achieved is 100%. That means the force captured or saved during the eccentric phase of the SSC (stretch-shortening-cycle) in the tendomuscular unit is completely being re-used in the conncentric phase and thus enahncing the power output of the muscle. Kangaroos are one of the most efficient animals regarding this issue, having a minimum on hysteresis, that is energy lost during the SSC due to their long tendons and even they do not achieve an efficency near 100%.