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One of the most common claims made by minimalist and barefoot runners (myself included) is that running in minimalist shoes (or barefoot) can be an effective tool for strengthening the muscles of the feet and legs. The idea is that constrictive, stiff, and overly cushioned modern footwear brace the foot, alter our natural biomechanics, and limit the ability of the foot and leg muscles to function naturally. As a result, these muscles get weak.
One of the first things I noticed when I began my own journey into minimalist running about two years ago was that my feet felt different. My first minimalist shoe was the Nike Free 3.0, and I can distinctly remember how I felt that the shoes were working my legs differently, and I had a sensation of “fullness” in my feet that I had never felt before (I can’t think of proper words to describe the feeling…). I knew something was happening, but I really wasn’t sure what it was. Jump ahead two years and I’m now quite certain that my feet have changed shape. I have no “before” pictures that I can compare to, but I find that shoes that used to fit me comfortably are now constricting and narrow, and if I had measurements, I’d guess that my forefoot is now wider than it used to be. No proof, but I believe this to be the case. I also feel like my big toe has migrated a bit medially, as if it were trying to create some additional space between itself and its smaller brethren.
All of this led me to begin doing some research to see just what we know about whether running in minimalist shoes can actually strengthen our feet and legs. It makes perfect sense, but the scientist in me wanted to see some data.
It’s fairly well established that living a shod life can alter the anatomy and function of our feet. For example, earlier today I read a fascinating study by a group of European researchers (D’Aout et al., 2009) in which they traveled to southern India and made anatomical measurements of the feet of habitually shod and habitually unshod individuals. They also took measurements from a group of Belgians for comparative purposes, since even the typically shod Indians wear mostly non-constrictive shoes like sandals (they also typically go barefoot as children). In addition to the foot examination, they had each individual walk over a pressure mat to examine how pressure is applied to the sole of the foot during normal walking.
What the researchers found was that the habitually unshod group had the widest feet, and both groups of Indians had longer feet when corrected for overall body size than the Belgians. In other words, the Belgians had short, scrawny feet compared to the Indians (take a look at Figure 3 from the D’Aout paper if you want to see what normal human feet that have not been deformed by footwear should look like). When they looked at plantar pressure distributions during walking, they found that the habitually barefoot group used more of the foot surface to disperse pressure (particularly in the region of the midfoot), whereas the Belgians tended to exhibit stronger and more localized pressure peaks under the heel and under the 2nd and 3rd metatarsal heads. The authors conclude their abstract with the following:
“The evolutionary history of humans shows that barefoot walking is the biologically natural situation. The use of footwear remains necessary, especially on unnatural substrates, in athletics, and in some pathologies, but current data suggests that footwear that fails to respect natural foot shape and function will ultimately alter the morphology and the biomechanical behaviour of the foot.”
They go on to state in the following in the Discussion section:
“…we suggest that walking and training barefoot or (if the substrate does not allow) using shoes that allow the foot to function as closely as possible as in the barefoot condition, could lead to performance benefits for athletes. Such performance benefits can be achieved, for instance, by increased muscular performance (as found by Potthast et al. 2005 when wearing minimal shoes) or as a result of potentially lower injury rates due to smaller peak pressures.”
The citation in this latter paragraph (Potthast et al. 2005) piqued my interest, so I hopped onto Google Scholar and found the reference, as well as a few others by the same authors. Turns out they are not journal articles, but rather are extended abstracts from a series of scientific meetings. Interestingly enough, Potthast and colleagues had conducted a study to see if training in the Nike Free shoes might actually lead to strengthening of muscles in the feet and legs when compared to training in a more typical shoe. Here’s their description of the study in “scientist-speak:”
“…it can be hypothesized that an especially designed training shoe with a multiple segmented outsole, mimicking barefoot movements and allowing barefoot-like exercises on hard surfaces, could induce different mechanical stimuli on foot and shank muscles. A biopositive adaptation should be advantageous in terms of injury prevention or performance enhancement. The purpose of this study was to identify an eventual training and adaptation effect in morphology and function on foot and lower leg muscles when wearing such a specifically designed training shoe.”
The scientists took 100 individuals, split them into two equally sized groups, and had them perform a series of exercises on a weekly basis in either Nike Free shoes or a conventional running shoe (for a duration of 6 months). The exercises included running, aerobics, skipping, and a variety of other things. They were also allowed to wear the shoes in everyday life if they so chose. They took a variety of measurements before the initiation of the study, including toe flexor strength (toe flexion is downward bending of the toes), range of motion of the 1st metatarsophalangeal joint (i.e., the joint at the base of the big toe/hallux), and the active path of motion of the same joint. They also took a subset of 25 individuals assigned to wear the Nike Frees and took MRI’s of the lower leg and foot to obtain information about muscle cross-sectional area (think of this as muscle belly size for simplicty’s sake).
What they found was that individuals in the conventional shoe group saw no change in toe flexor strength, whereas the Nike Free group saw a significant 20% increase in toe flexor strength. The experimental group also saw a reduced path of motion of the 1st metatarsophalangeal joint, which they suggested could be related to the higher strength of the toe flexors – stronger flexion of the toes would lead to less dorsiflexion (upward tow movement) during gait. With regard to MRI results, they found that the flexor hallucis longus (the muscle that flexes the big toe) was significantly larger after the experiment in those assigned the Nike Free. Although not significantly larger (very close), they found that both the abductor hallucis (the muscle that pulls the big toe away from the second toe) and tibialis posterior (a muscle the supports the arch and resists pronation) showed a trend toward size increase after the experiment for the Nike Free group.
In a second Abstract from the 2005 American Society of Biomechanics meeting, the same group reports additional data showing that plantar flexor strength (calf muscles) and dorsiflexor strength (tibialis anterior I presume) also increased in the Nike Free group.
I haven’t been able to find either of these studies published in full in a peer reviewed scientific journal, so they need to be taken for what they are as conference abstracts. However, they do suggest that a period of training in Nike Frees can increase muscle size and strength when compared to training in a more conventional shoe, at least for some muscles. What I find particularly compelling is that the subjects weren’t even necessarily running in the shoes very much – aerobics, skipping, side stepping, etc. were also included in the training plan. If doing these types of things can increase toe flexion strength, foot plantar flexion strength, foot dorsiflexion strength, and so on, one wonders what would happen if a more intensive running program were employed? Furthermore, the Nike Free isn’t even all that minimal of a shoe – it’s pretty cushy and retains a fairly sizable heel lift. I’d love to see a similar study that compares a group of runners using traditional shoes to a group that transitions from traditional shoes to something like the Vibram Fivefingers for six months.
After reading these studies, I recalled a light moment at the Running Injury Conference in Shepherdstown, WV that I attended back in January. Podiatrist Ray McClanahan was giving a presentation and he took off a shoe to show off the bulging belly of his abductor hallucis – he had “guns” in his feet! The abductor hallucis, as I mentioned, is the muscle that pulls the big toe medially away from the other toes. Make this muscle stronger, and this could provide the explanation for why many minimalist and barefoot runners claim that their big toe begins to migrate away from the others (into a position like that of the habitually unshod Indians discussed above, I might add…). I also begin to wonder if increasing the strength of the big toe flexor allows the big toe to take some load off of the metatarsal heads during stance phase, and whether this might also explain some of the difference between the unshod and shod plantar pressure differences shown in the D’Aout paper. Going further, perhaps weakness of this muscle combined with poorly adapted foot bones might contribute to some of the metatarsal stress fracture issues people occasionbally run into when transitioning into minimalist/barefoot running. Total speculation here, but interesting to put some pieces together and ponder.
At the end of this, my feeling is that the answer to the question posed in the title of this post is a definite “yes.” I’m left to conclude that my initial feelings after running in the Nike Frees way back in 2009 were probably correct – I think I was strengthening my feet and legs in ways that I previously had not.
What’s your sense – have your feet and legs changed in any noticeable way as a result of going minimalist or barefoot?