The effect of minimal shoes on arch structure and intrinsic foot muscle strength

Lets go back to the perennial question on foot muscle strength and traditionally shod running vs barefoot/minimalist running with the publication of this new research:

The effect of minimal shoes on arch structure and intrinsic foot muscle strength
Elizabeth E. Miller, Katherine K. Whitcome, Daniel E. Lieberman, Heather L. Norton, Rachael E. Dyer
Journal of Sport and Health Science; Available online 2 May 2014
Background
This prospective study explored the effects of endurance running (ER) in minimal versus standard running shoes on the foot’s superficial layer intrinsic muscles and the function of the longitudinal arch. Our hypothesis was that running in minimal shoes would cause hypertrophy in these muscles and lead to higher, stronger, stiffer arches.
Methods
The hypothesis was tested using a sample of 33 healthy runners randomized into two groups, a control group shod in traditional running footwear and an experimental group shod in minimal support footwear, whose feet were scanned in an MRI before and after a 12-week training regime. Running kinematics as well as arch stiffness and height were also assessed before and after the treatment period.
Results
Analysis of anatomical cross-sectional areas and muscle volumes indicate that the flexor digitorum brevis muscle became larger in both groups by 11% and 21%, respectively, but only the minimally shod runners had significant areal and volumetric increases of the abductor digiti minimi of 18% and 22%, respectively, and significantly increased longitudinal arch stiffness (60%).
Conclusion
These results suggest that endurance running in minimal support footwear with 4 mm offset or less makes greater use of the spring-like function of the longitudinal arch, thus leading to greater demands on the intrinsic muscles that support the arch, thereby strengthening the foot.

This study took a group of traditionally shod runners and allocated them to one of two groups: one group kept doing what they were doing and the other group were transitioned to minimalist shoes. At baseline and follow-up they measured arch height parameters, foot strike pattern and used MRI to measure the volume and cross-sectional size of selected foot muscles (as a proxy for strength).

The authors claim to have found:

  • more of the minimalist group where not heel striking at follow-up
  • increases in muscle volume were found at follow up in the flexor digitorum brevis in both control and minimalist groups; and in the abductor hallucis in the minimalist group
  • increase in muscle cross sectional area in the abductor digiti minimi in the minimalist group
  • no changes in arch height at follow-up (consistent with what I argued here)

Of the six muscle strength measurements (3 muscles measured by both volume and cross-sectional diameter); 1/6 showed an increase in the traditionally shod group; the other 5/6 did not change. In the minimalist group, 3/6 increased. That is hardly a compelling result and is not necessarily consistent with the conclusion reached by the authors in the abstract above and in the paper (though they did use the word ‘suggest’ in the abstract). Given that one muscle allegedly got stronger in the traditionally shod group, that is certainly more evidence that running shoes do not weaken muscles. This does not support the premise that these muscles are weak in running shoes or were weak to start with (which is what they imply), it just shows that they might get stronger in the minimalist condition.

Can the results they got be believed?
There are many red flags in this one and the study falls well short of the accepted gold standard and consensus for the reporting of trials (ie what the CONSORT statement and every textbook on randomized trials says you should do). This information is needed for the transparent reporting of trials so that a proper appraisal of the methods and results can be done. I have reviewed several studies recently that have fallen short on this: here, here, here and here.

What are the issues:

  • I see no evidence of an a priori sample size calculation. They may have done one, but did not report the justification. That does not mean I have a problem with the sample size, its just they did not report how it was arrived at. However, the cynic in me can not help but point out that the fan boys will have to reject the results of the above study due to the sample size – they rejected the recent Vibram and bone stress injury study based on its sample size of 36 being too small (it wasn’t) – its just if you going to reject that study for that reason, then you have to reject this one for the same reason (I don’t).
  • there is no indication if the study was single or double blinded. Did the participants know what the study was looking for (single blinding) and did those doing the measurements know which group the participant was in (double blinding). This should have been reported.
  • the handling of drop-outs in the study was not what is considered gold standard. Intention to treat analysis (recommended by the CONSORT consensus) was not done or at least a rationale or justification as to why it was not done was not given in the paper.
  • probably the most significant issue is that the analysis presented in the tables and how the results were reported in the abstract and full paper were based on within groups comparisons. That is NOT how you analyse a randomized trial. The whole point of randomized trials is to compare the outcome between the two groups, which they did not do. They just compared the outcome within each group.

These issues should have been addressed in the pre-publication editorial and peer review process. In this case, it appears to have failed. Until these issues are addressed the results can not be trusted. There are so many positives about this study, such as the way they transitioned the minimalist group; the choice of outcome measures; and the length of follow-up. It is a shame that a potentially good trial was ruined by not adhering to the consensus by which randomized trials should be reported and analysed.

Equally of concern is the biased introduction to the paper and those biases in the discussion which represent bad science. Many references cited in the introduction do not actually say what the authors are claiming they say. Those familiar with the references used in the paper will easily see the use of the wishful thinking fallacy. On other occasions authors have cherry picked references to support what they want to claim, ignoring many other references that show the opposite or do not support their claims. This really is bad reporting of science.

The whole basis of what they are discussing is based on the assumption that increasing the strength of the intrinsic muscles of the foot is a good thing and that minimalist running does this. I have no doubt that increasing muscle strength is a good thing and we know it goes a long way to preventing injury. But, is the premise that changing the running technique to increase that muscle strength a good thing? The whole thrust of the paper is that it is (ie they started this with a preconceived bias and that is not a good way to do science). It could be argued that if a particular running technique increases muscle strength, then it does so by increasing the activity of the muscles. Surely that is a bad thing? Surely an increase in muscle activity is a sign of an inefficient gait? I would have thought that an efficient gait would have less muscle activity. The authors were clearly biased that this was not the case. It may or may not be the case, but good reporting of research would be without those biases and address all the issues.

As always: I go where the evidence takes me until convinced otherwise, and this was potentially a good trial if the issues I raised re the reporting were done according to the CONSORT statement and if there were no preconceived biases and cherry picking of citations going on. This is a good example of bad science reporting.

POSTSCRIPT: I have had a few comments on Twitter and Facebook; basically:
I want to compare outcomes between doing x and y = good approach to doing science
I want to prove that x is better than y = bad approach to doing science.

Miller, E., Whitcome, K., Lieberman, D., Norton, H., & Dyer, R. (2014). The effect of minimal shoes on arch structure and intrinsic foot muscle strength Journal of Sport and Health Science DOI: 10.1016/j.jshs.2014.03.011

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About Craig Payne

University lecturer, runner, cynic, researcher, skeptic, forum admin, woo basher, clinician, rabble-rouser, blogger, dad. Follow me on Twitter, Facebook and Google+

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8 Responses to The effect of minimal shoes on arch structure and intrinsic foot muscle strength

  1. Ian Griffiths May 8, 2014 at 6:03 am #

    In total agreement regarding red flags on this one Craig. To name but a few more for me:

    * No mention of how sample/cohort was recruited

    * Runners in minimal running shoe group were given cues on running technique (told to use high cadence and avoid over stride) whereas runners in traditional group were not – then conclusions made that altered foot strike pattern was due to shoes…

    * Foot strength not directly measured yet still suggest in discussion that transitioning to minimal footwear can result in developing significant increases in foot strength (er… pardon?)

    * Constant (unreferenced) suggestion that increased stiffness from traditional footwear will interfere with “natural” mechanics of foot which is a bad thing, followed by the suggestion that training in minimalist shoes results in greater arch stiffness which is a good thing. If the stiffness increases the deformation decreases – end of story.

    Etc etc…

    • Craig Payne May 8, 2014 at 6:46 am #

      Thanks Ian

      “If the stiffness increases the deformation decreases”

      I missed that one! They really don’t understand it, do they?

  2. Kevin A. Kirby, DPM May 8, 2014 at 5:41 pm #

    After reading this paper, and the way it was written, it seemed to me like the authors had the goal of showing that “minimalist shoe running results in stronger feet”, regardless of what their experimental data showed. Craig and Ian have nicely listed a number of problems with the research design of this paper. However, my bigger concern is over the idea that it is ideal for the plantar intrinsic muscles of the foot to be larger for running.

    First of all, the authors assume that having larger plantar intrinsic muscles is actually advantageous to runners. We really don’t know if this is true since size of plantar intrinsic muscles has not yet been correlated either to increased running performance or decreased injury frequency in scientific research.

    Second, in the thousands of runners I have treated over the last three decades, I have yet to see an experienced runner have “weak plantar intrinsic muscles” regardless of whether they run in thick-soled running flats or racing flats (i.e. minimalist shoes). In general, compared to their non-athletic peers, runners have more strong plantar intrinsic muscles since they are running regularly and exercising more. The increased ground reaction forces of running demand more muscle contractile activity from the plantar intrinsics and will, thereby, increase plantar intrinsic muscle strength over time.

    Third, I believe it is neither biomechanically nor metabolically advantageous to have a foot have excessively large plantar intrinsic muscles for running. Since increased muscle mass of the foot increases the mass of the foot, and since the foot is at the end of the lower extremity where additional mass added to the foot will increase the moment of inertia of the limb, having increased plantar intrinsic muscle mass may actually make the individual slower and less metabolically efficient when running.

    It is well documented within the scientific research literature that adding mass to the foot with a shoe or adding weights to the shoe will increase the oxygen cost of running. In general, most studies show that for every 100 grams of mass added to a shoe, the metabolic efficiency of running will decrease by approximately 1%. Therefore, if we increase plantar intrinsic muscle mass by 100 grams since we have locked onto the idea (as the authors of this paper seem to be) that having larger plantar intrinsic muscles is better for all runners, then we may actually be decreasing the metabolic efficiency of running by 1%.

    Certainly, there must be an optimum muscle strength of the plantar intrinsic muscles for running where sufficient strength is present to prevent injury but the mass of the foot is kept to a minimum to reduce the moment of inertia of the lower extremity and, therefore, increase the metabolic efficiency of running. I wouldn’t be too sure that having more massive plantar intrinsic muscles is going to be such a good thing for most runners. However, after reading this paper, it seems to me like Lieberman and his colleagues decided that this was indeed the case well before their paper was written.

    Cheers,

    Kevin A. Kirby, DPM

    • Craig Payne May 8, 2014 at 8:37 pm #

      “decided that this was indeed the case well before their paper was written.” … thanks Kevin – that is exactly why this is how you do not do science.

  3. Craig Payne May 8, 2014 at 10:06 pm #

    I added a POSTSCRIPT above:

    I have had a few comments on Twitter and Facebook; basically:
    I want to compare outcomes between doing x and y = good approach to doing science
    I want to prove that x is better than y = bad approach to doing science.

  4. Nick Czmpitelli May 9, 2014 at 3:22 am #

    We have seen that intrinsic muscle atrophy leads to plantar fasciitis symptoms.

    Kevin, are you serious when you say that increasing muscle mass in the foot will make someone slower?

    It’s pretty clear that these intrinsic muscles have a purpose and can make for a more functional foot and reduce injury when strengthened. If they are insignificant and have no reason for being as you have claimed, then why do they exist, and why do they become stronger with running in general regardless of shoe type as Lieberman and colleagues have demonstrated? You admit they increase in size with running in general.

    Chundru U, Liebeskind A, Seidelmann F, Fogel J, Franklin P, Beltran J. Plantar
    fasciitis and calcaneal spur formation are associated with abductor digiti minimi
    atrophy on MRI of the foot. Skeletal Radiol. 2008 Jun;37(6):505-10.

    • Craig Payne May 9, 2014 at 3:41 am #

      Re Chundru et al: you do realise that correlation is NOT causation.

      “We have seen that intrinsic muscle atrophy leads to plantar fasciitis symptoms.” Nope. Care to back that up with some evidence, or is this just the wishful thinking fallacy.

      “more functional foot and reduce injury when strengthened” … if you going to make statements like that, then you probably should cite some references of research to back it up rather than just wish it was true.

      If these muscles do get stronger by minimalism/barefoot, then they must be working harder. I would assume that a muscle working harder is a bad thing during running and a sign of an inefficient gait. I would have though that an efficient gait is one in which muscle activity is reduced.

      I have no doubt that stronger muscles are a good thing and there is some reasonable evidence that its associated with a lower risk of injury; but should that strength come from additional exercises or a change in running technique which is potentially inefficient?

      We need data and good evidence, not bad science and certainly not the typical propaganda and rhetoric and continual use of logical fallacies such as the wishful thinking one.

    • Kevin A. Kirby, DPM May 10, 2014 at 4:58 pm #

      Dr. Czmpitelli:

      Like Craig said, you say that “intrinsic muscle atrophy leads to plantar fasciitis symptoms” but you use a study to back up your notion that this is the case that only showed that there was an association of abductor digiti minimi atrophy with plantar fasciitis. Just as likely is the fact that after patients in this study developed plantar fasciitis, they started limping which then caused, over time, atrophy in the abductor digiti minimi muscle. You aren’t serious, Dr. Czmpitelli, in believing that you can use a study that measures correlation to justify causation?

      Dr. Czmptelli, also please show me where I made the statement that “increasing muscle mass in the foot will make someone slower?” I think you should go back and carefully read what I actually did write. Let me make restate what I did say in my posting above:

      “Third, I believe it is neither biomechanically nor metabolically advantageous to have a foot have excessively large plantar intrinsic muscles for running. Since increased muscle mass of the foot increases the mass of the foot, and since the foot is at the end of the lower extremity where additional mass added to the foot will increase the moment of inertia of the limb, having increased plantar intrinsic muscle mass may actually make the individual slower and less metabolically efficient when running.

      It is well documented within the scientific research literature that adding mass to the foot with a shoe or adding weights to the shoe will increase the oxygen cost of running. In general, most studies show that for every 100 grams of mass added to a shoe, the metabolic efficiency of running will decrease by approximately 1%. Therefore, if we increase plantar intrinsic muscle mass by 100 grams since we have locked onto the idea (as the authors of this paper seem to be) that having larger plantar intrinsic muscles is better for all runners, then we may actually be decreasing the metabolic efficiency of running by 1%.

      Certainly, there must be an optimum muscle strength of the plantar intrinsic muscles for running where sufficient strength is present to prevent injury but the mass of the foot is kept to a minimum to reduce the moment of inertia of the lower extremity and, therefore, increase the metabolic efficiency of running.”

      Not once did I say that increasing muscle mass in the foot would make the runner slower. I said it may make the runner slower. Certainly, to anyone familiar with the scientific research on the effects of adding mass to the shoes of runners on their oxygen consumption rate during running, then my reasoning would make complete sense.

      By the way, the very first scientific study on this subject was done by one of my PhD professors in exercise physiology and one of my running buddies (who had a masters degree in exercise physiology) at UC Davis (who also broke the record and won the Western States 100 Mile Run a few times) while I was a cross-country and track athlete at UC Davis during the 1970s (Catlin ME, Dressendorfer RH: Effect of shoe weight on the energy cost of running. Med Sci Sports, 11:80, 1979).

      Back then, before I entered podiatry school in 1979, I was running 70-90 miles per week, was running marathons in the sub-2:35 range and raced in what we called “racing flats” which you would probably now call “minimalist shoes”. I also ran barefoot regularly over 35 years ago while doing intervals with the cross-country and track teams as did many of my other UC Davis Aggie teammates.

      What makes me laugh about the barefoot/”minimalist shoe” zealots and their minions is their infatuation with footstrike pattern and “heel drop” of running shoes and with their reverence for Chris McDougall and his book “Born to Run” that is perceived as being the bible of running and everything in it should be treated as the gospel truth.

      Coming from an older competitive runner like myself, it is rather comical to see the rise and fall of the barefoot running fad. Why? Because, 35 years ago, all of us UC Davis Aggie runners (and many other college distance running athletes from that era) ran barefoot occasionally, and regularly wore “minimalist shoes” to race and train in, and we were only worried about getting faster, beating the guys from the other teams in our league and trying to move up the ladder of the fastest runners on the team.

      In the 1970s, we never once worried about who was a heel-striker, who was a midfoot striker, who was a forefoot striker or which shoe had a thicker heel than another shoe. We just wanted to be as fast as possible and race in the lightest shoe we could that was also comfortable to race in. In other words, we could care less about what the guy behind us in the race ran like, what shoe they wore, etc….just so long as we beat them.

      In regards to Lieberman and colleagues article, and to your comments, in my 40+ years of being a long-distance runner and my 30+ years of being a sports podiatrist, I have never once seen a distance runner have weak plantar intrinsic muscles, whether they were injured or not. Therefore, the likelihood that strengthening the plantar intrinsic muscles in a runner will either make them faster or become less injured is, at best, an odd idea to me. My opinion is that this type of wishful thinking is more likely being fueled by the barefoot/”minimalist shoe” zealots and their hair-brained notions that somehow, by strengthening these tiny little muscles in our feet, it will make us run faster, run longer and never be injured.

      Finally, I know, Dr. Czmptelli, that you are a consultant for Vibram FiveFingers and, along, with Dan Lieberman, helped write a 13 page “step-by-step” manual on how to run in the Vibram FiveFinger shoe without getting injured. Therefore, I expected you to try to come to Dan Lieberman’s rescue for his rather odd paper on intrinsic muscle strength since you were coauthors in this 13 page manual that was meant to describe how Vibram FiveFinger shoe wearers could avoid getting the stress fractures and bone marrow edema that the study by Ridge et al very clearly demonstrated (Ridge ST, Johnson AW, Mitchell UH et al: Foot bone marrow edema after 10-week transition to minimalist running shoes. Med Sci Sports Exerc, 45(7):1363-1368, 2013).

      http://s3.amazonaws.com/VibramFiveFingers/Barefoot_Running_Brochure_R13_062211.pdf

      My question to you is why would any running shoe possibly need a 13 page manual in order for the runner to run safely in them if the shoe was not a well-designed running shoe in the first place? In the long history of running shoe production, no running shoe, ever, other than Vibram FiveFinger, has needed a 13 page manual to instruct the wearers of their shoe on how to stay uninjured by using their shoe.

      Now, Vibram has settled out of court for 3.75 million dollars due to making unsubstantiated health claims regarding the shoes that you are a consultant for and helped write a manual for. Were you and Dan Lieberman also named in this 3.75 million dollar class action suit since, very clearly, both of you helped perpetuate the unsubstantiated health claims that this company made for years regarding their shoes by writing this 13 page manual?

      So, Dr. Czmpitelli, why would you write such a manual hopefully knowing full well as a podiatrist, that Vibram FiveFingers shoes caused so many injuries in so many runners and that their health claims were not only untrue but also being used to sell a defective style of running shoe that caused injuries in hundreds to possibly thousands of unsuspecting runners?

      Myself, and many others, are very seriously interested in your reply to these questions.

      Cheers,

      Kevin A. Kirby, DPM
      Adjunct Associate Professor
      Department of Applied Biomechanics
      California School of Podiatric Medicine
      Oakland, California, USA

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