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FiveThirtyEight

Life

When I ran cross country in high school, the fastest guy on the boys team ran barefoot. I remember thinking this was wacky, especially given that a lot of the “cross country” courses were on asphalt. He had come to Connecticut from the West Coast, so I assumed at the time it was some kind of California thing. It wasn’t until many years later, in reading Christopher McDougall’s “Born to Run,” when I realized that this kid was onto something and, apparently, that the padded-shoe industrial complex was out to get me.

In “Born to Run,” McDougall sets out to learn why he is constantly getting injured as a runner and discovers a group of Indians in Mexico who can run incredible distances without shoes or sandals. The author concludes that running barefoot is the key to staying uninjured, and that virtually anyone can run marathon distances or more. Reading this book, it’s hard not to conclude that the only thing standing between you and a successful showing at Leadville, a 100-mile race in the mountains of Colorado, is the wrong pair of shoes. And it’s not surprising that barefoot running has trended way up since the book’s publication in 2009.

A major issue with actually running barefoot is that in most places, running around without shoes is a recipe for glass in your foot, or worse. Fortunately, people’s desire to run barefoot did not go unnoticed by the market, and barefoot or minimalist running shoes, such as Vibram FiveFingers and Nike’s Free, have abounded. Marketing materials for these shoes imply health benefits, including stronger foot and leg muscles and fewer running injuries. (Vibram, however, mentions on its website that the shoes might not be appropriate for over-pronators. Runners over-pronate when their feet roll excessively inward, and they may benefit from a more supportive shoe.)

But recently, the bubble has started to burst, underscored most clearly by a legal settlement in May against Vibram for overstating the benefits. The class-action lawsuit argued that the quality of the scientific evidence in favor of minimalist shoes had been exaggerated by the company. In the settlement, Vibram did not admit wrongdoing but agreed to pay $3.75 million to compensate those who purchased FiveFingers shoes. The reaction of many toe-shoe runners is probably similar to my husband’s as he looked over my shoulder to see I was writing this: “Wait. Do I have to get rid of my shoes?”

The answer is no. Little would suggest that those who are happily running in minimalist running shoes should stop, but the answer to whether there is any reason to start is a bit more complex.

Let’s start at the beginning. Prehistoric man did not have cushioned running shoes, and humans have evolved to run long distances. This has led some to conclude, perhaps logically, that running barefoot is the optimal way to run. On the flip side, technology has improved many aspects of our health — an infant mortality rate below prehistoric norms of 50 percent comes to mind — so it’s not obvious that running with padded shoes couldn’t also be an improvement. Also, prehistoric man didn’t exactly leave notes about his excruciating shin splints, so we don’tknow about injury rates.

What is clear is that the mechanics of running are different if you are barefoot vs. in traditional shoes. Runners wearing standard padded running shoes typically land on their heels and then transition to the toe as the stride completes (this is called a rear-foot strike). Runners who are barefoot, and those in minimalist running shoes, typically land on their front foot first (a front-foot strike). Shoe type is not perfectly predictive of strike pattern, but the correlation is high.

What is also pretty clear is that for a given distance and speed, people use less energy — perhaps 5 percent or so less — running barefoot or with minimalist shoes. This is something people figured out a while ago. You’d never see an elite runner clomping along in a race in giant padded shoes.

The debate is more complicated when it comes to the role shoe type plays in injuries. The difference in motion — rear vs. front-foot strike — stresses different parts of the body. Several papers summarize the common injuries, which biodynamics suggest would be associated with the two strike patterns. A rear-foot strike is associated with higher risk of knee pain, possibly higher risk of shin stress fracture and more plantar fasciitis, a common running injury that causes heel pain. Toe stress fractures and Achilles tendonitis are more commonly associated with front-foot strike.

Based on this evidence, it is possible that the rate of injury could be higher with either shoe type. The injuries may not be the same, but it’s not obvious whether people prefer a toe stress fracture to a shin stress fracture or vice versa.

The evidence one would like to see — and presumably what the court would have liked to see from Vibram — is some large-scale randomized data on injuries with minimalist vs. traditional running shoes. An ideal experiment would randomly assign half of the group studied to use minimalist shoes, and half to stay with traditional shoes, and we’d follow their injury rates over time. It’s not impossible to imagine such a study, but it hasn’t taken place yet. This is not to say that there is evidence to favor padded shoes, either. One review article searched the medical literature for evidence to support the use of running shoes with elevated and cushioned heels, and concluded that no studies of this kind existed.

The best evidence we have, as I see it, comes from two small studies. The first is a randomized study of treatment for plantar fasciitis. Twenty-one participants were randomly assigned to exercise programs with either a traditional running shoe (control group) or a minimal running shoe (treatment group). The minimal shoe group reported faster reduction in pain than the control group.

The second study is observational: Researchers studied 52 college runners and compared injury rates for those who had a rear-foot strike pattern with those who had a front-foot strike pattern. It is worth noting that this paper does not actually compare shoes, although we know that shoe choice and strike pattern are correlated.

The authors find that those runners who use a front-foot strike have fewer injuries overall. This result is driven by the fact that injuries typically associated with a rear-foot strike are more common among rear-foot strike runners, but those associated with a front-foot strike are actually not more common among the front-foot strike runners. This suggests that although the biodynamics of front-foot strike suggest susceptibility to these injuries, the data does not suggest they are more common in this group. The researchers also show that rates of traumatic injuries (e.g. muscle soreness and strains from speed work) are similar across the two groups, which is a nice way to test whether one group is more injury-prone.

To give a sense of the magnitudes: The study finds a rate of five moderate or severe repetitive injuries per 10,000 miles among front-foot strikers and 8.7 per 10,000 miles among rear-foot strikers. In other words, if you run 5 miles a day every day, you’re predicted to suffer 0.9 injuries per year if you’re a front-foot striker and 1.6 injuries if you’re a rear-foot striker.

I found this paper useful and somewhat compelling, although the study is small and randomization data would be more useful. It also is worth noting that the research is partially funded by Vibram, although the authors said the funding sources didn’t have any role in the research design or their analysis.

And so there is very little evidence either way, although I’d say that if you are running with whichever type of shoe and are happy with it, there is no reason to switch. On the other hand, if you’re experiencing an injury associated with the type of shoe you use, then you might consider switching.

On the all-important question of what to do if you are new to running and have to pick, I’d ultimately lean slightly toward the minimalist option. Unless, of course, you do your running on glass shards.

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