The New York Times Blog


In recent years, many barefoot running enthusiasts have been saying that to reduce impact forces and injury risk, runners should land near the balls of their feet, not on their heels, a running style that has been thought to mimic that of our barefoot forebears and therefore represent the most natural way to run. But a new study of barefoot tribespeople in Kenya upends those ideas and, together with several other new running-related experiments, raises tantalizing questions about just how humans really are meant to move.

For the study, published this month in the journal PLoS One, a group of evolutionary anthropologists turned to the Daasanach, a pastoral tribe living in a remote section of northern Kenya. Unlike some Kenyan tribes, the Daasanach have no tradition of competitive distance running, although they are physically active. They also have no tradition of wearing shoes.

Humans have run barefoot, of course, for millennia, since footwear is quite a recent invention, in evolutionary terms. And modern running shoes, which typically feature well-cushioned heels that are higher than the front of the shoe, are newer still, having been introduced widely in the 1970s.

The thinking behind these shoes’ design was, in part, that they should reduce injuries. When someone runs in a shoe with a built-up heel, he or she generally hits the ground first with the heel. With so much padding beneath that portion of the foot, the thinking went, pounding would be reduced and, voila, runners wouldn’t get hurt.

But, as many researchers and runners have noted, running-related injuries have remained discouragingly common, with more than half of all runners typically being felled each year.

So, some runners and scientists began to speculate a few years ago that maybe modern running shoes are themselves the problem.

Their theory was buttressed by a influential study published in 2010 in Nature, in which Harvard scientists examined the running style of some lifelong barefoot runners who also happened to be from Kenya. Those runners were part of the Kalenjin tribe, who have a long and storied history of elite distance running. Some of the fastest marathoners in the world have been Kalenjin, and many of them grew up running without shoes.

Interestingly, when the Harvard scientists had the Kalenjin runners stride over a pressure-sensing pad, they found that, as a group, they almost all struck the ground near the front of their foot. Some were so-called midfoot strikers, meaning that their toes and heels struck the ground almost simultaneously, but many were forefoot strikers, meaning that they landed near the ball of their foot.

Almost none landed first on their heels.

What the finding seemed to imply was that runners who hadn’t grown up wearing shoes deployed a noticeably different running style than people who had always worn shoes.

And from that idea, it was easy to conjecture that this style must be better for you than heel-striking, since presumably it was more natural, echoing the style that early, shoeless cavemen would have used.

But the new study finds otherwise. When the researchers had the 38 Daasanach tribespeople run unshod along a track fitted, as in the Harvard study, with a pressure plate, they found that these traditionally barefoot adults almost all landed first with their heels, especially when they were asked to run at a comfortable, distance-running pace. For the group, that pace averaged about 8 minutes per mile, and 72 percent of the volunteers struck with their heels while achieving it. Another 24 percent struck with the midfoot. Only 4 percent were forefoot strikers.

When the Daasanach volunteers were asked to sprint along the track at a much faster speed, however, more of them landed near their toes with each stride, a change in form that is very common during sprints, even in people who wear running shoes. But even then, 43 percent still struck with their heels.

This finding adds to a growing lack of certainty about what makes for ideal running form. The forefoot- and midfoot-striking Kalenjin were enviably fast; during the Harvard experiment, their average pace was less than 5 minutes per mile.

But their example hasn’t been shown to translate to other runners. In a 2012 study of more than 2,000 racers at the Milwaukee Lakefront Marathon, 94 percent struck the ground with their heels, and that included many of the frontrunners.

Nor is it clear that changing running form reduces injuries. In a study published in October scientists asked heel-striking recreational runners to temporarily switch to forefoot striking, they found that greater forces began moving through the runners’ lower backs; the pounding had migrated from the runners’ legs to their lumbar spines, and the volunteers reported that this new running form was quite uncomfortable.

But the most provocative and wide-ranging implication of the new Kenyan study is that we don’t know what is natural for human runners. If, said Kevin G. Hatala, a graduate student in evolutionary anthropology at George Washington University who led the new study, ancient humans “regularly ran fast for sustained periods of time,” like Kalenjin runners do today, then they were likely forefoot or midfoot strikers.

But if their hunts and other activities were conducted at a more sedate pace, closer to that of the Daasanach, then our ancestors were quite likely heel strikers and, if that was the case, wearing shoes and striking with your heel doesn’t necessarily represent a warped running form.

At the moment, though, such speculation is just that, Mr. Hatala said. He and his colleagues plan to collaborate with the Harvard scientists in hopes of better understanding why the various Kenyan barefoot runners move so differently and what, if anything, their contrasting styles mean for the rest of us.

“Mostly what we’ve learned” with the new study, he said, “is how much still needs to be learned.”

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