Dr. Lieberman of Harvard University has yet another new study out, Strike type variation among Tarahumara Indians in minimal sandals versus conventional running shoes. As you can see from the study title, he visited the Tarahumara Indians, who were featured in Born to Run.
What he found is that conventional running shoes really do weird stuff to feet.
Not that we didn’t already know that.
But he puts some numbers on it.
The Tarahumara are well-known for long-distance running, usually while wearing huaraches, thin pre-Columbian sandals. But they are no less subject to modernization than any other peoples, and a lot of them have started running in conventional running shoes. Of course, conventional running shoes have thick, padded heels and arch support.
That means that visiting them gives one a marvelous opportunity to make some scientific measurements and see if there are any differences in their feet and they way they run.
None of us will be surprised to learn that running shoes make a difference.
One of the things Dr. Lieberman did was to bring down some decent cameras and paraphernalia to record the foot landing techniques of the runners. He tested 23 people. 13 of them were regular huarache runners, and 10 regularly wore conventional running shoes. Lieberman then analyzed the video to classify the landings as either rearfoot (landing on the heel), midfoot, or forefoot.
Here are the results:
It can’t be much clearer. Among these people, who run constantly, the footwear really affects how you land. And don’t forget that landing on the heel creates sharp transient forces throughout the body.
While he was there, Dr. Lieberman also measured the stiffness of the arches of the Tarahumara in his study. I think it should be pretty obvious that a stiffer arch is a stronger arch, and stronger is better. Stiffer means that all the muscles and ligaments are doing their jobs they way they are supposed to.
There are actually a number of indices that have been developed to measure arches and their stiffness. The first one is the “arch height index” (AHI). It is the “Dorsum Height” (the height of the foot measured at half the length of the full foot) divided by the “Truncated Foot Length” (which runs from the center of the first metatarsophalangeal joint to the back of the heel—basically the foot minus the toes).
[Picture from “A Novel Arch Height Index Assessment: Intra-Rater Reliability” by C.J. Richards, K. Card, J. Song, and H. Hillstrom of Temple University.]
The stiffness then measures how much the AHI changes from when one is standing (that is, under load) to when one is sitting (no load). Here’s the formula for Lieberman’s “Arch Stiffness Index” (ASI):
Obviously, if the foot didn’t change at all, the stiffness would be infinite (dividing by zero).
What Dr. Lieberman found was that those who ran using the huaraches had an ASI about twice that of those who ran in conventional running shoes: 1607.2 ± 744.1 vs. 823.6 ± 223.7 (with high statistical significance). Oh, and by the way, Dr. Lieberman also found pes planus (fallen arches) in two of the runners who wore conventional shoes.
I should mention that, as opposed to the other study I wrote about, this study was a retrospective study, not a prospective study. That means things weren’t set up in advance to carefully and randomly choose control groups, etc.. It also means that it’s possible that the runners with normally weak arches chose conventional running shoes over huaraches because of those weak arches. Ditto for those with the fallen arches. It’s also possible that more of those who naturally ran with a heel strike deliberately then chose conventional running shoes.
On the other hand, this is really suggestive. Combined with that other study—which, I should mention, was the published version of the Master’s Thesis of Elizabeth Miller, who was the lead author on the paper—it really strongly indicates that this arch weakness is the fault of the shoes. And combined with other studies, it also strongly indicates that conventional running shoes really do change how folks land when running.
And it’s not surprising at all (or shouldn’t be). If you are supporting a muscle so that it isn’t being used, no wonder it gets weak!
But that is something that just doesn’t seem to get across to so many people.