Abigail Daley participated in the Naked Foot 5K in Chevy Chase last June. Dozens of styles of “minimalist” shoes attempt to approximate barefoot running in various ways. (Matt McClain/FOR THE WASHINGTON POST)

Americans spent $59 million on “minimalist” running shoes last year, on the premise that the most healthful way to run is the way people have done it for thousands of years: barefoot.

Running barefoot, according to the hugely popular 2009 book “Born to Run” and a landmark 2010 study of Kenya’s famous Kalenjin distance runners, forces most people onto their forefeet, which nature designed to absorb the considerable impact that running places on feet and lower legs. Traditional running shoes of the past 40 years, in contrast, encourage runners to land on that cushy, raised heel, possibly contributing to lower leg problems.

But now a group of George Washington University researchers, who tested a different population of barefoot African runners, has determined that most of them naturally strike the ground with their heels.

Kevin Hatala, a doctoral student in anthropology at GWU, expected his group’s study of the Daasanach people of northern Kenya to jibe with Harvard researcher’s Daniel Lieberman’s conclusions about the Kalenjin.

Instead, “we found the opposite to be true,” Hatala said in an interview. “In the group we were looking at, the majority of them were rear-foot striking at their preferred endurance running speed.”

For his study, published in the Jan. 9 issue of the online journal PLOS One, Hatala asked 19 men and 19 women to run at a variety of speeds over pressure plates that measured the impact forces they generated. At higher speeds, some of the Daasanach switched from a heel strike to a forefoot strike, but even then, heel-striking was more typical.

Hatala was reluctant to speculate why his findings differed from the prevailing wisdom. In addition to the effect of speed, running style could be the result of information that is culturally transmitted from generation to generation. Or it might have something to do with the predominant surface where each group lives. Hatala and Lieberman are at the early stages of comparing their data.

“I guess what we found really interesting about this is it directly shows that there is not one way to run barefoot,” Hatala said. “We have a lot more to learn about how people who are barefoot run and what might be the best way to run barefoot.”

In an e-mail, Lieberman noted that his study found some barefoot heel-strikers as well, and that the Daasanach are mainly tall, lanky goat herders who don’t run nearly as much as the Kalenjin, who own many of the world’s distance-running records. A larger study Lieberman is preparing for publication confirms his earlier work, he said.

Currently, dozens of styles of minimalist shoes, which attempt to approximate barefoot running in various ways, comprise 10 percent of the $588 million running shoe market in the United States, according to Scott Jaeger, senior account analyst for the Leisure Trends Group in Boulder, Colo. Sales of minimalist shoes are up 303 percent between November 2010 and November 2012, compared with a 19 percent increase in running shoe sales overall in the same period.