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Thursday, March 1, 2012

More Barefoot Statistics: It Swings Both Ways

I was going to be done with the whole "analyzing a barefoot running study" thing for a while. Then someone lobbed a scientific softball, and I couldn't help but take a swing. Sweat Science (Runners World's new sciency blog...formally just a random sciency blog) reported on a new study out of The University of Colorado dealing with whether running barefoot or in light cushioned trainers is more efficient. We all know the answer to that question right?

No...no you don't. According to this study, although barefoot runnres more efficiency consume oxygen at a given pace than those wearing heavy cushioned trainers, they do NOT do so more efficient than those running in very light-weight cushioned trainers. In fact, light-weight cushioned trainers appear to make oxygen usage more efficient to the tune of around 3-4%.

Both this, and the fact that they never made a Rush Hour 3, are shocking to me. Okay...neither really shock me. Here's why.

First, Chris Tucker is annoying. And there are only so many times you can do the whole kung-fu crimefighter with bumbling sidekick thing. See as reference Shanghai Knights.

Alright, now that my obligatory Jackie Chan joke is out of the way, let's get to disecting this study. Starting with the ways I feel the study's results could be a little skewed. The biggest way the study could be off involves the study participants' familiarity with barefoot running. The study involved 12 runners who were reported forefoot strikers, as well as experienced barefoot runners. The study used quote-unquote "experienced" (yes I realized I spelled out quotations and then used them) barefoot runners in order to eliminate the possibility that results wouldn't be affected because folks didn't know how to run barefoot.

However, the study defined "experienced" as someone who runs at least 5 miles per week barefoot. Now two of my friends participated in this study, and I DO considert them to be experienced barefoot runners.  But otherwise, someone who runs 5 miles per week barefoot is NOT necessarily an experienced barefoot runner. I have coaching clients who run 5 miles in their first week of barefoot training.

Why does it matter? In my experience, folks that run around 5 miles per week barefoot are still doing things like working out form inefficiencies, figuring out how to prevent hot spots and blisters, and building up their plantar skin. In other words, these folks are only running 5 miles per week barefoot because that's all they are capable of running. These folks are not the most efficient barefoot runners to begin with.  Not only that, but they are likely more efficient in light-weight or minimalist shoes to begin with.

A better way to eliminate the experience problem: instead of defining experience in terms of miles per week, define it in terms of years of experience or total barefoot miles ran. I have no problem believing that someone who has run 1000+ miles barefoot is experienced. Same thing with someone who has a couple of years of barefoot running under their belt. Barefoot running efficiency develops over time. If you want living proof, watch Ken Bob run sometime. It's like butter.  Butter with lots of facial hair in it...

I wonder though if that beard affects wind resistance.

Although, even assuming that all study participants were indeed experienced barefoot runners, study results could still be flawed if these runners weren't HABITUAL barefoot runners. If these folks primarily run in shoes, then they likely don't run as efficiently barefoot as they do in shoes. Habitually running in shoes has the negative side effect of throwing off your barefoot running form.  This is true regardless of level of experience. Every winter when I'm cooped up in minimal shoes for months on end, I develop a bunch of bad habits. Most noticeably, I have a more forceful footstrike that expends more energy than I otherwise would in the summer when I'm predominantly barefoot.

Aaaaaaanyway...even assuming we had a proper crop of experienced barefooters, the study still could be affected by the running surface. According to the study abstract, study participants ran on a treadmill. Now I get that most running studies are performed on a treadmill to eliminate terrain as a factor in any results. But for barefoot runners, it introduces several possible inefficiencies. For one, treadmill running is not conducive to proper barefoot running form. That's because the belt is moving at you instead of remaining fixed like the ground. So to remain upright and running you must decelerate your body with each step instead of propelling yourself forward. This requires a slightly different footstrike, which you adopt somewhat naturally in order to avoid sheering forces between your toes and the belt (i.e. in order to get rid of that burny feeling). This footstrike is also less efficient.

Apparently treadmill running makes you look and dress like a fashion-forward Olive Oil.

I won't go through the exact form change in detail, except to say that it requires you to use your calf and foot muscles more than you otherwise would. Here's an article from Jason Robillard on treadmill running tips if you're interested. He calls the phenomenon "toeing off". Though even if you don't toe off on a treadmill, your normal barefoot running form will no doubt be affected negatively. Try it sometime.

The other negative of barefooters using treadmills is heat generation. Even if you follow the tips in Jason's article, running on a treadmill is going to generate significant friction between you and the belt. The result will be an increasingly hot belt. As anyone who's run on hot asphault can tell you, running on a hot surface with bare feet will significantly deteriorate one's form and use a ton of energy. Again, efficiency suffers.

AFTER POST EDIT: I was informed by a rather passionate commenter that the participants wore thin yoga socks during the "barefoot" portion of the study.  I don't think this much affects my critique.  Though it does blunt my point about heat generation.  Though in my experience, there is no sock thick enough to dissipate all the heat from a treadmill belt.  If anything, it just gives you hot feet AND hot socks.

Okay fine. Now just because I found a few flaws in the setup of this study doesn't mean that I don't agree with its results. Namely, that weight and cushioning in running shoes effect efficiency. The weight part is pretty obvious. If you run with one pound weights strapped to your feet, you're going to have to work harder than if you have 1/8 lb weights strapped to them. Less weight on your feet equals less oxygen consumption.

The cushioning part is a little less obvious. The study authors proposed that cushioning made participants efficient in two ways. First, they noted that the runners took longer strides in cushioned trainers (3.3% longer). Second, they argued that in absence of cushioning, the runners had to expend energy in order to absorb the impact of their stride; impact which would otherwise be absorbed by the cushioning.

I think that both hypothesis are somewhat incorrect. Although a lengthened stride will allow runners to travel further on average with each stride, we also know that as you increase your stride you also increase vertical impact loading rate (good article talking about why loading rate matters). In not-as-nerdy terms, as your foot strike travels further away from your center of mass, you increase the stress on your legs. You'll be working harder, which would lead to a decrease in efficiency...not an increase.

Not to mention, what the authors are essentially saying is that cushioning immediately changes running form in ways a person can't necessarily control. It appears that it didn't add much in the way of inefficiency to the form of study participants, but I doubt that will be true of everyone. I recall another study where putting habitual barefooters back into cushioned trainers resulting in them reverting back to a heel strike! Quite a change indeed.

The "cost of cushioning" hypothesis is more likely to be correct, though not to the tune of the 3-4% improved efficiency as reported. I agree with the authors that cushioning does lead to a reduction in impact forces. And this leads to the body using less energy to absorb impact. However, it also USES energy by creating an unstable running surface. The foot and ankle muscles have to work harder to stabilize on the cushioning than they would barefoot on a hard, flat surface.  Of course, we don't have hard numbers to indicate the net result. 
Taking all of this into account, is it really more efficient to run in light-weight cushioned trainers or minimalist shoes than barefoot? I would say that it depends. For an experienced barefoot runner on a smooth, flat surface like asphault, or on a non-technical trail? I bet the difference is negligible or that barefooters are actually more efficient. For those with less experience, or for anyone on rough terrain or a treadmill, certainly a shoe will have some advantage. Running over rough terrain barefoot is a gasser regardless of experience level.

A shocking or revoluationary finding? Not really. Of course if you looked at the chatter about this study among running gurus, you'd think this study was a knife in the heart of the barefoot movement. That's ridiculous. If anything, it plays into what most barefooters have said for a long time regarding shoes: there's a time and a place for them.

Much ado about nothing.  Yeah...pretty much.  But I needed a blog post to use that Jackie Chan picture.  And it's nice to have science to back up what most barefooters already know. 

That's a from me this week citizens! Cheers and beers!


  1. Oddly enough, mine swings to the left.

    Ok I couldn't resist.

  2. "In non-nerd terms, as your foot strike travels further away from your center of mass, " not to be too wonky, but if that's in non-nerd terms I'd hate to see you go into detail. Is Chris Tucker getting any acting gigs these days?

    1. Okay...how about "not that nerdy" terms? Sometimes I forget how far up the nerd tree I've climbed.

  3. I've got the full study and am going through it. I see some problems with your critique:

    1. The barefooters wore very thin anti-slip yoga socks so heat from friction shouldn't really have been an issue. But I suppose barefooters will now say that invalidates the study because they weren't really barefoot.

    2. A longer stride doesn't necessarily mean they're reaching further ahead of COM. It just means they've increased the horizontal distance they travel from step to step i.e. they've increased time in flight phase. If they were reaching further ahead of COM they would have begin to heel strike which the authors don't report happening.

    Increased time in flight phase could account for decreased energy usage. And even if your hypothesis that they use more energy landing on cushioned shoe during footstrike is correct, over the entire gait cycle they are using LESS energy. Global effects trump the effects at any one particular point.

    3. You say when running shod in winter your footstrike is more forceful so you expend more energy. How do you measure this? RPE? Do you fatigue quicker? Higher HR? I would assume a more forceful footstrike means you're running faster, is that the case? Being a habitual barefoot and minimally shod runner, wouldn't your body have learned how to run economically in either condition? (knowing nothing of your training history or experience, I assume you've been running in both conditions for at least a few years)

    4. Your point referring to the habitual barefooters going back to a heel strike in shoes is one reason the researchers only included mid or fore-foot strikers. They wanted to control for the possible effect of foot-strike on economy and efficiency.

    Also that study used a more traditional cushioned shoe. This study used an ultralight, minimal cushioning shoe the Nike Mayfly. Big difference!

    The authors theoretically reverse engineered a shoe with some fancy math and propose that a shoe weighing 129 g with some cushioning would offer a statistically significant metabolic advantage over barefoot running. The Mayfly is 16 g heavier.

    But you're right in that we should be careful in extrapolating the results to a general running population. Sample size was small and the authors admit this in the discussion. Statistical analysis revealed they would have needed at least 15 more runners for statistical significance.

    You accuse "running gurus" of misinterpreting the results and there may be truth in that. But many barefooters have also been guilty of misinterpreting research as well.

    Overall I think this was a decent study that is moving the science forward. It's not about proving if barefoot or shod running is better. It's about understanding how the different conditions affect the body and then knowing how to use the information to devise appropriate training programs for different runners.

    And many running coaches, myself included (not necessarily gurus) would probably agree with you, there is a time and place for barefoot running ;-)

  4. Wow...someone got a little passionate. I suppose I'll respond in the same bullet point form

    1. Barefooters wearing socks: Yes...the study is now completely invalid. Move along now...

    2. Increased stride length: You're assuming I know waaaaay more about body mechanics than I actually do. I'm a lawyer man.

    3. My claim that I develop bad habits over the winter like hitting the ground harder: I don't need a HR monitor to know I am hitting the ground harder. I measure it by feeling my foot as it hits the ground. It's harder. I don't need a fucking force plate to know when I'm slapping my foot against the pavement and when I'm not.

    4. Using forefoot strikers as controls: Thanks for putting 2+2 together for me.

    5. The Nike Mayfly thing: is cool.

    6. The whole "running guru" thing: You essentially just said "I know you are but what am I". Very persuasive.

    Sorry...I lost interest after that. You're taking me way too seriously man.

  5. http://www.imdb.com/title/tt0293564/ = your argument is invalid.

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