The science of barefoot running form hit the ground somewhat simply at first. In a January, 2010, Nature article, “Foot Strike Patterns and Collision Forces in Habitually Barefoot Versus Shod Runners," Harvard evolutionary biologist Daniel Lieberman and colleagues said that traditionally unshod populations likely ran with a soft forefoot or midfoot strike. They said that rearfoot strikes, or heel strikes, involved higher collision forces that could lead to repetitive stress injuries over time. Since staying healthy was important for survival, and survival for early humans may have included running long distances to forage or hunt, they hypothesized that forefoot or midfoot strikes were probably more common for barefoot runners. They also said that forefoot or midfoot strikes might protect today's runners, who often heel strike, against a high degree of impact-related injuries.
The scientific debate about running form picked up, with a lot of back and forth about the economy, injury rates, and performance benefits of foot strike patterns and running. Lieberman and co. added traction to their theory in 2012 when they published a study that said college cross-country runners with rearfoot strikes had a higher rate of repetitive stress injuries than those with midfoot and forefoot strikes. A 2012 lawsuit brought against Vibram for deceptive advertising about the supposed health benefits of their shoes added attention and debate. The science about foot strike patterns and barefoot running is young and far from conclusive.
This month, things got more convoluted. Lieberman's 2010 Nature study, which found a high rate of forefoot strike among traditionally barefooted runners, focused on one particular group of people, the Kalenjin of Kenya. A January study published in the journal PLOS One, “Variation in Foot Strike Patterns During Running Among Habitually Barefoot Populations,” looked at another group of traditionally unshod runners—the Daasanach of northern Kenya—and found they favored rearfoot striking.
Kevin Hatala of George Washington University and colleagues tested the footstrike patterns of 38 traditionally barefoot Daasanach adults and found that the majority ran with a rearfoot strike at endurance speeds. They impacted the earth with some part of their heels 72 percent of the time, a midfoot strike in 24 percent of trials, and forefoot strike four percent of the time. "We were surprised to see that the majority of Daasanach people ran by landing on their heels first and few landed on their forefoot,” Hatala said in a press release. “This contradicts the hypothesis that a forefoot strike characterizes the 'typical' running gait of habitually barefoot people."
Of course, it’s not that simple. When Hatala and colleagues had the runners increase their speed, the incidence of midfoot and forefoot strike picked up significantly, though not at the rates witnessed by Lieberman with the Kalenjin.
Why might the Daasanach run with more of a rearfoot strike? Hatala offers up some theories in the article. The Daasanach run at a slower endurance pace (8:08 per mile) than the Kalenjin (4:33–5:16 per mile). But that alone likely doesn't explain the difference, as the Kalenjin predominantly forefoot struck at a wide range of paces (4:28–11:11 per mile). Aside from running faster, the Kalenjin also run longer. They top distances of 12 miles a week, where the Daasanach run less—Hatala doesn't have an exact figure for their distance. Maybe a combination of the Kalenjin’s faster speeds and greater distances led them to evolve a forefoot strike that involves less impact on the legs to reduce stress and the possibility of injuries? Or, it could be that the foot strike patterns actually come down to something much simpler: the type of earth underfoot. If the Daasanach run on a softer substrate than the Kalenjin, they might be more comfortable with a higher impact rearfoot strike. There is a lot to consider.
The takeaway is that not all barefoot people run with a particular strike. Factors ranging from speed, to body type, to training distance, to training frequency, to the softness of the earth likely influence footstrike patterns. Though Halata and colleagues did find that more impact occurred to the legs during rearfoot strikes, he says that more study is needed to sort out how and why different running strike patterns are favored by different groups.
He thinks the best way to tackle that problem is with teamwork. "We are now working in collaboration with the Lieberman Lab at Harvard to figure out why there is such a stark contrast in foot strike patterns between these two habitually unshod groups," he says.