Welcome to the Science of Sport, where we bring you the second, third, and fourth level of analysis you will not find anywhere else.

Be it doping in sport, hot topics like Caster Semenya or Oscar Pistorius, or the dehydration myth, we try to translate the science behind sports and sports performance.

Consider a donation if you like what you see here!

Did you know?
We published The Runner's Body in May 2009. With an average 4.4/5 stars on Amazon.com, it has been receiving positive reviews from runners and non-runners alike.

Available for the Kindle and also in the traditional paper back. It will make a great gift for the runners you know, and helps support our work here on The Science of Sport.

Thursday, May 16, 2013

A minimalism/barefoot fad and inconsequential footstrikes?

Minimalism as a fad and inconsequential footstrikes?

Two articles of interest, both connected to the barefoot running/minimalist shoe debate, and I promised on Twitter that I'd give a few more detailed thoughts.

"It appears this fad is pretty much over" - minimalist shoe sales decline

The first was this article, in Runnersworld, which quotes an industry watcher as saying that the minimalist trend is over.   This is based on the reported stat that in the first quarter of 2013, running shoe sales grew in the high single figures (8%, perhaps), driven largely by sales of motion control shoes (25%) and stability shoes (10% increase).  This overcame a drop in the sale of minimalist shoes, which "declined in the low teens" (so let's call it a drop of 13-14%, perhaps), and which now makes up only 4% of total running shoe sales.  The industry watcher concludes "it appears this fad is pretty much over".

An interesting statistic, particularly when you consider that in previous years, it was minimalist shoes that were the fastest growing segment, while the stability and motion-control categories were stagnant or falling.

So, a reversal of sorts, but one that should not be surprising, given how overhyped the barefoot movement had been post "Born to Run".  Also of note is that the end of the article makes mention of a shift away from the barefoot style minimalist shoes towards more conventional shoes that are lighter and lower to the ground than in years past.  This may be the lasting legacy of the 'barefoot bubble', because it has driven the realization that the bulky, heavy and excessively cushioned shoes were not necessary and probably didn't do what they purported to.  The shoe industry as a whole has adjusted its paradigm, and that is certainly a good thing, in general.

The end result, once the dust settles further, is that we've been pulled more towards the middle, which is always a good place to be when it comes to the complex physiology and biomechanics of individuals.  This is an oft-repeated point here on the site, I've said it too many times, but the notion that one solution would work for everyone is clearly false, and one of a few current examples of trying to swing the pendulum from one (wrong) extreme to the other equally wrong extreme (the 10,000 hours vs genes, and low-carbohydrate diet debates are the other two).

An expanding bubble and a sustainable niche

At the New Balance South African launch of their minimalist shoe in about 2009, I remember sitting in the audience, and a journalist asked the question of whether minimalism might just be a fad?  My response to that was that it would not die out like a fad, because it was clear that many people were achieving great success in the barefoot shoes, and that this group, however small, would sustain the market segment.  Whether or not it continued to grow at the rates it was back then would depend on a) the relative success people achieved in minimalist/barefoot shoes, and b) the strength of the scientific evidence and how well it was communicated to runners.

It's clear that now, admittedly only 4 years on, that the scientific evidence has not provided a compelling enough case to drive the companies into an even bigger push for minimalism, but has helped inform the shift to ligher, flatter traditional shoes.  The evidence is, at best, ambiguous, and the field still needs a long-term, prospective injury study.  The unanswered questions of 2009 remain unanswered, and a few tenuous links between loading rate and injury prevalence based on footstrike will not be enough to change the direction of a multi-billion dollar shoe industry, which has too much inertia for the anecdotes of a few (however outspoken) success stories to knock off course.

The former requirement, people's success, is a more interesting phenomenon.  I do believe that the hype of minimalism, driven by the almost evangelical (and irresponsible, I have to add) volunteer sales job being done by many of those who had succeeded, spawned a movement of "barefoot/paleo" runners, many of whom were destined to fail.   Why?  Because they may simply not be suited to minimalist running in the first place, and perhaps this is a group who needs shoes as much as the successful minimalist runners do not.

That's probably a radical idea for some, but as much as we have heard arguments for how 'evil' the shoe industry was for advocating that everyone needed cushioning, air, gel, pro-moderater, roll bars and the like, I wonder if any have considered that when you swing the pendulum in the opposite direction and advocate barefoot/minimalism, you are doing exactly the same thing?  The reality is that some people may well belong at the extremes, but many more belong somewhere in the middle, and there has been little nuance in the discussion.

Perhaps the market figures are beginning to reflect that nuance, with the realization that not everyone will succeed without the cushioning provided by traditional shoes.  Just a thought.  The point is, the market was expanding so rapidly that the uptake of barefoot and minimalist running was bound to claim its fair share of casualties.

The trouble is we don't know these numbers.  What proportion of runners have tried and failed, compared to those who have succeeded?  Given the downturn in sales of minimalist shoes, and that only 4% of the market is minimalist shoes, I'm guessing that the latter group is smaller than the former - more fail than succeed.  The problem is that those who try and fail slink off to the store and go back to traditional shoes, whereas those who succeed become outspoken, leading to a large reporting bias.

I can, at this point, pre-empt the response to these injured runners and minimalism failures: "Those people obviously didn't reduce their training enough, and allow their feet and bodies to adapt to the new style".  And of course, this is likely to be true in many of these instances.  Running injuries are caused by running - there is a threshold for injury, and when it is exceeded, the runner breaks down.

The point is that the shoes were marketed as a way to reduce the injury risk.  That is, they would change the injury threshold, so that a person could do the same training as before without injury.  And yes, it would be unreasonable to expect a person to go straight from traditional shoes into minimalist shoes, maintain the same volume, and get the promoted upside.  So there was an inevitable period of 'compromise' where the runner would need to drop training volumes and invest in learning the skill.

My problem with this is three-fold.  First, there's no guarantee of an upside to begin with.  For some individuals, it works, without question.  For others, it may not, and for reasons we don't understand, some people may be incapable of running without traditional shoes, regardless of how long they take.  There is little recognition of the fact that some people may be unable to learn the skill, or adapt, but the tool was never to blame, only ever its user.

Second, the sacrifice to succeed may be unreasonable.  You have to ask whether it is reasonable to expect a person to reduce themselves to beginner status for months, when there is no guaranteed benefit, a very large potential downside or risk, and when the alternative - cut training volume by 20% and get stronger in the supporting muscles - might be equally effective within weeks?  I don't believe this is reasonable, and so for some, it may not be a viable alternative, given questions of leverage and time.

And third, and the reason I think it has been irresponsibly promoted is because you can't advocate a change and not understand the dosage for it.  A few months back, a study was published where the scientists prescribed barefoot running over 10 weeks using the guidelines of a minimalist shoe maker to the letter.  The result was that 10 weeks later, every single one of the runners had indications of stress fractures in their feet, some with full blown stress fractures.  To that, I recall the response was that the "advice was not conservative enough".  This is the ever-shifting goal post of barefoot running advice, and to me, the point is that we just don't know who succeeds, or how much (or how little) training they require.  That's why it's irresponsible for the zealous few who succeed (at most 4%, remember) to be so vocal about it.  They change their names to "Barefoot XYZ" and drag everyone with them, blaming the end-user for their failures.  It's just not a viable product, and sales figures support that.

That said, it's clear that there are people, perhaps many, who have succeeded and they should continue to run in minimalist shoes.  I count myself as one of them, for the record, lest it seem that this is an attack on minimalism.  I've nothing against the concept, just its advocacy and the obnoxious way it is pushed on people (as I feel about carbohydrate hunters).  I tried every extreme, from straight barefoot (did Mount Kilimanjaro barefoot, just to check!) to flat racing shoes, and I think I've found a balance that works for me.  I would not advocate it to anyone.  Rather stick to education, and let people discover what works for them.  As for the industry, they've recognized the shift, and responded to it with lighter, more flexible shoes, and that's definitely a good thing.  For most people.

"Neither footstrike is advantageous" - a study on footstrike and injury

The second interesting piece of news was Amby Burfoot's piece on a study just done in the US Army, where researchers tracked injury prevalence and performance in 342 recruits.  The Army often produce very important studies on injury, because potential confounding factors and risk factors for injury are so much easier to control effectively.  The study is being presented at the American College of Sports Medicine meeting in a few weeks, and so should be in a journal soon.  Then it will be possible to review more substantially, but a surface reading shows some interesting findings to discuss for now.

It found no difference in performance between the heel-strikers (87% of the group) and the non-heel strikers (that is, mid and forefoot), and no difference in injury prevalence or severity (measured as days off training, as is typically done in the field).  The trend was for the non-heel strikers to report more injuries, in fact, which is interesting because the last few years have seen a rise in the "heel striking is bad" argument.

The link between barefoot running and footstrike, incidentally, is that very early on in the evolution of the barefoot running idea, it was proposed that it's not necessarily what you wear on your feet that matters, but how you land.  This was based on the observation that when barefoot, most runners adopted a forefoot landing.  Ergo, forefoot/midfoot is better, heel-striking to be avoided. I won't point out how circular that logic is, but I will make the following points, which I believe explains the Army study results.

First, not everyone responds the same way to a change in footwear.  Some people, when running barefoot, continue to heelstrike.  These people show enormously high loading rates and impact forces, and so every (admittedly theoretical) link we have with injury says that they will have increased risk of injury when barefoot.

Second, the interesting thing is that when you put these people in shoes, their loading rates and impact forces come down to the same level of a barefoot runner landing on the forefoot/midfoot.  To give you some numbers, they go from about 400 BW/s to 100 BW/s.  The runners who one would consider "good" barefoot runners because they land on the midfoot are at 80 - 100 BW/s.  Peak ground reaction forces look similar.

The point is that shoes make a huge difference to this risk factor, and they do this for a very particular subset of runners only - it's only the runners who are heel-strikers when barefoot who see this benefit.  When you put a midfoot striker in shoes, they show basically no change compared to when barefoot.  And that is interesting, because it points to a benefit of shoes, at least with respect to the narrow link between kinetics (forces) and injury.

Third, and most interesting, is that in these runners, the ground reaction forces and loading rates come down despite even greater heel-striking than when barefoot.  In other words, you put them in cushioned shoes, they land even further back, with a more dorsiflexed ankle, and their force profile improves relative to when barefoot.  It improves so much that they are actually similar to barefoot runners, and the foot-strike doesn't matter.

We know this because we've just finished a study looking at this exact thing - a PhD student of mine,  Nicholas Tam, has just submitted a paper looking at this individual variability as a key to the shoe prescription debate, and we believe it would explain why foot-strike doesn't matter in the shod, but not barefoot, condition.  This, like the benefit of barefoot running, has probably been oversold.

Once Nic's first paper is published, I'll go into much more detail about what we did and found, but the key points are:

  1. There is huge individual variation in the biomechanics response to barefoot running.  Some people go in totally the "wrong direction" with respects to the kinetics that are supposedly linked to injury
  2. Those individuals, the barefoot heel-strikers who don't seem to adjust at the ankle to help absorb landing forces, may be unsuited to barefoot running, but benefit from cushioning provided by shoes, to the point that they are similar to barefoot runners or midfoot strikers, shod or not
  3. The footstrike doesn't affect the injury risk factors in shoes, only when barefoot
So, returning to the Army study, there are of course many factors other than footstrike related to injury. But the way that the footstrike has been overplayed as a cause is perhaps exposed by this finding, and it can be explained anyway as the possible beneficial effect of shoe cushioning.

Ultimately, injuries will be caused by exceeding a threshold of adaptation, and footwear, biomechanics and factors like flexibility and muscle strength may contribute to this threshold.  It can be shifted, higher or lower, but not in a manner that is yet predictable or formulaic, because it's too complex to link A to B.  The Army study reveals, through the lack of a finding, that the paradigm of A to B is over-simplified, and the drop in sales of minimalist shoes further suggests that we're now seeing the pendulum settle somewhere towards the middle, away from the extremes, which do tend to embrace over-simplified paradigms and theories.

Quite where this leaves us is difficult to say.  It's not attractive to say "each to his own" and that we should embrace complexity and nuance.  "Born to Run" sold well, in part, because of its extremism, just like the low-carb diet and the 10,000 hour concept work when they exclude every other reasonable possibility.  It's go big, go alone, or go home science.  It's also wrong.  

In the shoe debate, we still need the long-term prospective study on injuries, and I'd still argue that everyone should try "less shoe", in the sense that more flexible and lighter is probably better.   At worst, it becomes a training modality.  At best, a new way to run.