I am assuming that you have all seen the claims made many times in the barefoot running books, You Tube video’s, blogs and forum posts that barefoot running can increase the height of the arch of the foot due to an increase in muscle strength. Yet you never see any evidence quoted to support the claims as there is none. There certainly are testimonials and the occasional before and after photo posted of an increase in arch height¹ (not to mention just how easy it is to fake pose those photos).
There is no evidence that barefoot running or minimalism leads to an increase in the height of the arch of the foot. I am not denying the testimonials from some barefoot runners that it does happen, but testimonials are just anecdotes and anecdotes are not data or evidence. I have also seen (but unfortunately did not bookmark) a couple of forum posts from barefoot runners commenting that they were disappointed that their arch height did not increase with the barefoot running. This means one set of anecdotes can cancel out another set of anecdotes, which is why we need evidence.
I have never brought into the wishful thinking from so many barefoot bloggers that an increase in the intrinsic muscle strength affects the height of the arch for a number of reasons:
- There is one study that has shown that there is no relationship between muscle power and arch height; another study showing that exercises to increase the strength of those muscles did not affect arch height; however another unpublished abstract reported a decrease in arch height with intrinsic muscles exercises! The evidence certainly does not support the contention that strengthening the intrinsic muscles of the foot leads to an increase in arch height.
- One small study (only 5 subjects) that was presented at the 2011 ACSM meeting showed no change in arch height after 6 months of minimalist running (abstract here). The study has not been published in full for proper peer review and appraisal.
- When you look at the size of those muscles on anatomical dissection, they are extremely small. How can muscles that small have any impact on the height of the arch of the foot?
- We have this abstract from the 2012 ACSM meeting that showed that: “barefoot running does not result in greater activation in these muscles compared to running shod. This suggests that barefoot running may not result in strengthening of the foot intrinsic muscles“.
- If the intrinsic muscles are to increase the height of the arch, they do so by plantarflexing the metatarsals. These muscles run pretty close to parallel with the metatarsal, so have a very poor lever arm to plantarflex them. So how can those tiny muscles with a really poor lever arm come close to doing that, especially against body weight and the magnitude of forces generated during gait?
- The EMG studies on flatfoot show that the intrinsic muscles are very active, much more active than in a ‘normal’ arched foot. While I am the first to acknowledge that EMG does not equal muscle strength, but certainly would ask if they are more active in a flat foot, then they must be stronger than in a ‘normal’ arched foot where they are less active.
- We also know from neurological situations that the opposite can happen. In the diabetic foot when there is an atrophy of the intrinsic muscles (the ‘intrinsic minus foot’) and in very early CMT when only the intrinsic muscles are affected, they tend to actually develop a high arched foot. This suggests that a weakening to the intrinsic msucles of the foot lead to a higher arch structure.
So I would suggest it really is wishful thinking that barefoot or minimalism increases the height of the arch of the foot via the mechanism of increasing strength of the intrinsic muscles of the foot. The evidence and the points raised above do not support that contention.
So what might account for the increase in arch height that some barefoot runners report (and document with photographs)?
Follow this thought experiment:
- When the rearfoot pronates or everts, the medial side of the forefoot can not go through the ground, so the forefoot supinates or inverts relative to the rearfoot to stay flat on the ground. It is this supinated or inverted position of the forefoot on the rearfoot when the rearfoot is pronated or everted that leads to the lowering of the medial longitudinal arch.
- Over a period of time, the soft tissues adapt to the position, so that when you place the rearfoot back into a vertical or neutral position, the forefoot is going to be in an inverted position relative to the rearfoot due to the soft tissue contracture. Those who are familiar with the theoretical constructs will know that what I am describing is a forefoot supinatus (as opposed to the osseous version of a similar looking foot of forefoot varus). Do not try and do this test of keeping the rearfoot vertical yourself to see where the forefoot is as its deceptive due to the tibialis anterior muscle firing and dorsiflexing the medial column of the foot.
- Lets assume someone with this forefoot supinatus transitions to barefoot running or minimalism. The posterior tibial muscle works harder due to the forefoot or midfoot strike pattern and this will invert or supinate the rearfoot more when running.
- More rearfoot inversion means that the medial column of the forefoot/first ray is going to plantarflex more, so over a period of time the soft tissue contracture of the inverted forefoot on the rearfoot will stretch out and the medial longitudinal arch will take on a higher arch profile.
This would easily account for the increase in arch height anecdotally reported by many barefoot runners and has nothing to do with the strength of the intrinsic muscles of the foot. It would also account for those who do not get an increase in arch height, in that they possibly never had the soft tissue contracture of a forefoot supinatus in the first place (maybe they had the osseous version of forefoot varus that no amount of minimalism or muscle strengthening can overcome). Also, this plantarflexion of the first ray will enhance windlass function of the foot, which also affects arch height. I am also going to take a guess and speculate that this may be what Test#3 that I had no idea was about if you are ready to make the transition to minimalism may have something to do with – those with a very high force pronating the rearfoot and causing the forefoot supinatus would probably fail this test and they also are probably not going to be able to make the transition to minimalism. They would fail the test, not because of the rationale that was proposed as being behind the test, but because of the soft tissue contracture of the forefoot supinatus.
This mechanism would also account for any therapeutic benefits and increase in arch height from the foot strengthening woo being marketed by Barefoot Science.
I like to model and do thought experiments, as long as they are consistent with the evidence. As always, I go where the evidence takes me until convinced otherwise
POSTSCRIPT: A study present at the 2013 ACSM mtg that reported the results of 39 runners after a transition to minimalist running shoes. They found no change in arch height (more).
1. I just did a search to find some of these but could not find them. I have seen several and did not bookmark them. If anyone has a link, please contact me as I would like to link to at least one of the before and after photos.