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Sunday, July 28, 2013

Alan Oliveira runs 10.57s. Leg length or something else? Over to the IPC and IAAF

Alan Oliveira runs 10.57s: Is it leg length, or something else? Over to the IPC/IAAF

Hot on the heels of a 20.66s World Record for double-amputees in Lyon a week ago, Alan Oliveira of Brazil, the fastest double amputee in the world, today destroyed his own 100m World Record with a performance of 10.57s in the London Olympic stadium.

I wrote about his emergence as the heir to Oscar Pistorius last week, describing the implications of his incredible improvements in 2013.  He last week won the 100m, 200m and 400m titles in the IPC World Championships, and is now a staggering 0.44s faster than the next fastest in history at 100m (Pistorius).  The improvement has come within the last two months, because prior to that, Oliveira's best 100m time was 11.33s.

The leg length - in play, but a red herring

Of course, the current debate is all about his legs, and more specifically, their length.  That is a red herring.  While partly true, there are many reasons to suggest that what Oliveira has achieved in 2013 is not the result of excessively long legs, but some other factor, which has already been proven to exist by scientific research.  Unfortunately, the IPC seem intent on pursuing length as the critical one, with new rules controlling length to be announced soon.

It's unclear what this will mean for Oliveira in the short term, but the problem is that they won't solve the larger problem, and the next athlete to come along with once again push the sport into the same dilemma.

Let's look at the leg length issue in a bit more detail.

London 2012 flashback 

When he defeated Pistorius in the London 2012 200m final last year, the accusation made by Pistorius was that he "couldn't compete with Alan's (long) stride length".  An easy explanation to test, because all it took was counting the strides, and it turned out that Oliveira's stride was not all that long.  In fact, Pistorius took fewer strides than Oliveira, and thus had the longer stride - 92 steps vs 98 steps, for a step length of 2.2 m vs 2.0 m for Pistorius and Oliveira, respectively (remember that a stride is two steps - I counted steps, but report strides later in the discussion).  And the final 100m showed the same pattern - Pistorius' average step length was 2.3 m, compared to 2.2 m for Oliveira.

So, stride length, at least at a superficial level, is not where the advantage came from back then, and it's not the sole explanation now either.

That said, it would be incomplete and false to suggest that Oliveira's leg length should not be the subject of some scrutiny.  In the week leading up to that 200m final, Oliveira revealed in an interview that he had recently increased his blade length by 4cm, taking him from a racing height of 1.77m to 1.81m, and he was clearly relatively taller than his rivals.

To understand what all that means, let's consider how the IPC set the maximum allowable leg length for double amputees.  First of all, it's not an easy task to do - there is no such thing as a "normal height", and when someone does not have legs, then trying to be specific about how tall they would have been is a complex exercise in dealing with ranges.  That's because we don't all share the same limb proportions.

There is an average ratio of say, arms to height, and a similarly average ratio of femur length to total leg length, but these averages don't often apply to elite athletes.  One example is Michael Phelps, the world's greatest swimmer, who stands 1.93m tall and remarkably, wears the same length pants as Hicham el Guerrouj, the world record holder in the mile, who stands only 1.75m tall!

That is, a difference of 18cm in height, with the same leg length.  Such are the variations between people.  One is a swimmer, one is a runner, and they are arguably born to excel in their specific events by virtue of completely different leg to total height ratios.  For pages and pages of similarly mind-blowing stats, I would highly recommended David Epstein's book, "The Sports Gene", which is due out this week.

But for now, let's leave it at the fact that the IPC cannot simply say "You should be X cm tall based on your arm length".

Instead, what they have done is establish a maximum allowable height for each double amputee.  The image below, which was released in the aftermath of the London 2012 controversy, shows the height limits for the key players in this debate.  It invites four thoughts:

Thought # 1 - taller is not necessarily better, and that has important implications

First, notice that Oliveira is allowed race at 185.4 cm, whereas Pistorius was able to go to 193.5 cm.  Presumably, that's a limit based on arm length, modified and improved by femur length to give a total height, which is the absolute maximum for someone who has exceptionally long legs relative to their body (like el Guerrouj).  We know that in London, Oliveira was 181cm, so he was 4cm short of the limit.  He was thus perfectly legal, as I'm sure he is now.  The issue is thus not cheating, but perhaps whether the limits are 'fair'.  

To address that, it's interesting to wonder about why he would stop at 181 cm?  If you're going up from 177 cm as he did, and if longer legs mean better performances (as people somewhat simply suggest), then go to the limit of 185.4 cm. More length, more speed?

The answer to that question is that at some point, going longer becomes counter-productive.  That's because the start becomes so severely compromised (as we saw with Oliveira in London), as well as balance around the bend, that the overall performance gets slower.  Top end speed may be greater, but the net result of longer limbs is less balance and therefore slower times.  Thus, there exists a "sweet spot", an optimal length for each athlete, and that's why none of the top double amputees are competing at their maximum allowable height.  Pistorius, for instance, races at 186 cm.

Thought # 2 - athletes discover the sweet spot by testing, so everyone is "optimized"

The implication of Thought # 1 is that the elite athlete have discovered their optimal sweet spot, because if they didn't, they go maximum length to find more top end speed.  We know from the PR around Pistorius that testing on blades is extensive - he traveled to Iceland often, and representatives of these carbon fiber manufacturers visit athletes for field testing regularly.

Part of the process is discovering how far below the limit the athlete should stop.  So for instance, we should be asking how Oliveira knew to stop at 181 cm prior to London, and why Pistorius was at 186 cm in the first place when he could have gone to 193 cm?  Why not 189 cm?  They had room to play with, but decided not to use it.  The answer is that they're optimized at those 'sub-max' heights.

For Oliveira, however, that may have changed since 2012.  It's conceivable that since his breakthrough (remember that he was just 19 in London last year) he has had more time and more technological support, and thus more opportunity to work out his ideal racing height.  

One source at the IPC reported to me earlier this year that Oliveira had in fact gone shorter, and thus discovered a much faster start and bend performance, driving his times down.  Others are saying he is now even longer - perhaps right up to his 185.4 cm limit.  A curve ball in this debate is that between 19 and 20, he may have grown, and so his upper limit of 184.5 cm from London may have increased, allow him more to play with.  

His 100m performance improvements suggest shorter, because his start is so much better, unless he has improved his balance and co-ordination spectacularly in the last 12 months.  However, we don't know what height he has raced at.  The IPC will, unless they have been grossly negligent in getting the blades measured, and that is surely inconceivable given the obvious focus on them.  They'll have to consider this information as they decide what to do next.  Which leads me on to point 3...

Thought # 3 - the IPC have to change the rule, but how effective will it be, and what do they base the change on?

It's clear that if the current progression continues, the IPC and the IAAF will have to reassess the situation of double-amputees racing in the able-bodied events.  Oliveira won the 400m title at the World Champs this weekend, but with a less than stellar time.  He said after that he doesn't train for the longer distance.  With an Olympic Games coming up in his own country, and with 3 years of preparation, maturity and strength to gain, it's almost inconceivable that he won't at least attempt to run in both Olympic and Paralympic competitions, emulating Pistorius.  Perhaps he will focus on the 200m - another half a second improvement on his 20.66s WR puts him into a final there, with possibilities of a medal should three years produce similar improvements to 2013.  Given that he is only 20, and clearly still in a period of rapid improvement, such an improvement is well within the realms of possibility. 

If he does jump up to the 400m, his chances are even better - the time lost at the start can be recovered over the final 350m, and his top-end speed, which must surely be comparable to Usain Bolt's, as well as remarkable sustained speed in the second half, should see him go considerably faster still.

So, what are the IPC and IAAF to do?  Refer again to the table above, and remember that those maximum height allowances are based on data collected from hundreds if not thousands of people to establish a range of human "norms".  If the IAAF and IPC decide to change them to make Oliveira race at a shorter height, they would have to justify it by saying something along the lines of "We are now adopting mean or average height rather than allowing for extreme individuals within the normal population".  That is, they would have to pretend that extremes like Phelps or el Guerrouj don't exist, and I can't see how that is legally or scientifically defendable.  You have to allow for cases at the extreme end of "normal", which is why the answer to that apparently simple question "What is a normal height?" is so very complex.

Alternatively, they could modify the guidelines slightly, perhaps to 1SD above means, and reduce Alan Oliveira's maximum allowable height subtly.  If it meant he was forced to drop to say, 181cm, he'd be at the same height he was at in London, and that means more of the same debate and performances. 

The point is this:  Because none of the athletes are at the maximum allowable height (see Thought #2), any change in the policy will have to be drastic, or it won't affect them anyway.  And drastic changes mean re-writing the understanding of human anthropometry, possibly discriminating against individuals who are normal but 'extreme', and may thus be impossible to implement.  All in all, very sticky for the IPC.

Thought 4: Leg length possibilities for Oliveira

And then finally, as I return to where I began, this discussion of length may be something of a red herring.  Again, there is no doubt that as the legs get longer relative to total height, the person is more likely to be a successful runner.

However, Oliveira has achieved almost a second of improvement in the 100m within one year.  His 200m performance trajectory is similar.  That invites three possibilities:

  1. He is still racing on the same length blades as London (height 181cm).  In this case, his improvement is solely due to training, co-ordination and normal development.  One can still say he has an advantage, but his improvement is distinct from it.

  2. He has changed up, and gone to longer legs, then I find it hard to believe that 3 to 4cm (he only has this to play with, it's not as though he can race at 195cm - see table above) can contribute to that kind of performance.  This is particularly true given that any increased length must surely compromise the start and bend, and so the effect is even larger.  Simply put, it cannot be solely due to running "taller" in 2013

  3. He has changed down, and found a better "sweetspot" that gives him a better start and bend performance, faster overall, with some accepted reduction in top speed.  If this is the case, and he's running at say 179cm, then it's even more of a problem for the IPC and IAAF because whatever they plan to change in their guidelines would need to be even more drastic.
What if stride length is not the factor at all?

But what if it is not in the length at all?  What if that simple exercise of counting his strides, and comparing them to Oscar Pistorius' in London 2012 actually hints at the solution?

Remember, that night, Pistorius took 49 steps on the bend and 43 steps in the home straight.  That is a step length of 2.0 and 2.3 m respectively.  Oliveira, on the other hand, had average step lengths of 1.92 m on the bend and 2.2 m on the straight.  In a race of absolute stride lengths, Oliveira is second-best.

The key, however, is the stride length relative to body height - someone who has excessively and disproportionately long legs will have a longer stride relative to their height, so you can partially test this 'accusation' by comparing stride length to total length.

So, running that logic for 2012, if Pistorius, at 186 cm, takes 230 cm steps, his step length to height ratio is 1.24.  Oliveira, at 181 cm with 220 cm steps, is at 1.22, and so in fact, Pistorius' steps are actually longer, not only in absolute terms, but also relative to his height.  This is the primary reason that I wasn't convinced that Oliveira's advantage was stride length back in 2012, and I'm not convinced now (though I will allow for the possibility that he has since increased his length - see Thought # 4).

The answer is more likely stride speed, not length. And that closes the loop

The ratio is however significant, because it says that Oliveira's advantage, which is now even greater than it was in London 2012, comes not from stride length, but the other important factor - stride speed.  It is the turnover of his limbs that separates Oliveira from the rest of the world, and which has made him a realistic medal chance in able-bodied competitions.

And why is that important?  Well, it closes the loop, bringing us full circle, because the scientific research on Oscar Pistorius showed that the advantage of double-amputee athletes, as a result of super-lightweight carbon fiber blades, is that his limb repositioning speed was "off the biological charts".  Those words were written by Prof Peter Weyand, who tested Pistorius and suggested a 10-12 seconds advantage because of limb reposition times he had never seen before, even in 100m Olympic champions.

Simply, the double-amputee was able to move his limbs so fast that he could then afford to spend more time on the ground, and generate significantly lower forces than able-bodied runners who were going the same speed as him.  The "athletic limit" to sprinting, according to Weyand, a world leader in sprint mechanics, is the ability to apply huge force to the ground.  Pistorius was able to run world class speeds without that limit existing, because his ultra-lightweight limbs allowed him be break another limit - the speed with which the legs could be moved.

Alan Oliveira has taken that to a new level.  When a man is running a 200m race and his strides are about 10% shorter than his rival's, then the only way to run faster than the rival is to have stride speeds that are 10% or more faster.  That's the Oliveira advantage - extra-ordinary speed of leg movement.  He is able to capitalize on the technology more effectively than any runner before him, and may also be able to generate force more rapidly than his predecessors.  The result is less time on the ground, less time in the air to reposition the limbs, and 20.66s and 10.57s performances.

Oliveria - validating the theory, vindicating the research, with no end in sight

Oliveira is, simply put, the validation of scientific theory, and he vindicates the predictions made about what would happen when the pool of athletes with access to carbon fiber blades expanded to include superior athletes.  This was inevitable - it's a rapidly growing sports category, and this is a great thing.  If only they'd kept them separate based on objective evidence, rather than the emotion of the Pistorius case.

Oliveira will one day be beaten by the next generation of double amputee, who will be even faster, and will then re-ignite the same debate.  The problem for the IPC and IAAF now is that they will have to reassess their guidelines in order to slow the runner down.  In other words, Oliveira is too fast, so we have to rewrite the rules.

Effectively, what they would be doing is setting a bar, at say 20.50 s for a 200m and 45 s for a 400m, and saying 'We welcome your participation, but just don't be too fast, or we'll have to change our rules to make you slower'.  It is analogous to putting weights on the bicycles of the top men of the Tour de France, to make the race more competitive, or make Djokovic and Murray play with wooden rackets to slow their dominance of tennis.

Well, the end is not in sight, because just as Pistorius was not going to be the pinnacle of athleticism on prosthetics, why should Oliveira be?  This is progress.  It's human progress.  A normal progression of ability as better athletes emerge.  The IPC and IAAF are looking at the technology, when they should be looking at how the heck they managed to duff the case against carbon fiber blades in the first place. 

Final word - a lot of the above discussion revolves around the very basic analysis of the London 2012 200m final, where I counted the strides for Pistorius and Oliveira.  What should happen is a similar discussion, in even more detail, now that Oliveira is rewriting the record books.

However, that won't happen, because the powers that be don't seem to recognize the importance of gathering the data to inform this kind of discussion.  I can appreciate that they have bigger issues, and may not have the resources to do it themselves.  Certainly, they are custodians over more than just one category and three of its events.  

However, in the build up to the Lyon IPC World Championships, I tried to approach the IPC for permission to analyse Oliveira's 100m and 200m races.  I wanted split times at 10m intervals, so that we could discover just how much time he lost at the start, when he hit top speed and how that top speed compared to Usain Bolt's (I suspect it is the same, or faster).  However, the IPC were not as enthusiastic, and so the study concept was never approved.

What a pity, because now we have to guess - we don't know his leg length, or the limit, or just how he put those world records together.  In time, maybe this debate will force those facts into the open, and that will be a good thing.  But until the evidence emerges, we talk about average stride lengths and stride speeds, which suggest that it's not solely about longer legs (as the public and even some rivals are still proclaiming), but about stride speed.

The evidence is out there, waiting to be found.  For Pistorius, the evidence was found - it showed clearly what was happening.  Why is it paid no attention?

In time, perhaps it will be.  Today, in 10.57s, Oliveira guaranteed that it would be.  There's much still to learn.