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To shoe or not to shoe? Whereas the shod runner (left) strikes with the heel of his foot, barefoot runners land on the front and middle of their feet, blunting the impact on their bodies.

Daniel Lieberman/Harvard University

The Shocking Truth About Running Shoes

Haile Gebrselassie, the world's fastest marathoner, once said of his early career, "When I wore shoes, it was difficult." A new study reveals why: Humans run differently in bare feet. Researchers have discovered that sneakers and other sports shoes alter our natural gait, which normally protects us from the impact of running. The finding offers new insight on how early humans ran and raises concerns that sports shoes may promote more injuries than they prevent.

About 2 million years ago, the ancestors of modern humans evolved the physiological "equipment" for running--long legs, large buttocks, and springy structures in the feet, among other features. Athletic shoes weren't invented until the early 1900s, and it wasn't until the 1970s that they found widespread popularity. So how did humans manage to run comfortably before the invention of purpose-built footwear?

Daniel Lieberman, a human evolutionary biologist at Harvard University--and an avid runner--decided to find out. He and colleagues looked at more than 200 shod and unshod runners in the United States and the Rift Valley Province of Kenya, which is known for its great endurance runners. The volunteers represented a spectrum of shoe experience, including adults who had grown up wearing shoes, those who had grown up running shoeless but who now wore shoes, and those who had never worn shoes at all. Lieberman's team arranged a trial in which each group ran shod (either in ASICS GEL-Cumulus 10s or in their own shoes) and bare and measured their running gait and the impact on their bodies.

The researchers noticed a difference right away. Whereas shod runners tended to land on the heel of the foot, barefoot runners landed on the ball of the foot or with a flat foot. The unshod runners' style causes more flex in the foot's springlike arch, ankle, and knee and engages more foot and calf muscles, blunting the impact on the body and making for a more comfortable "ride." As their feet collide with the ground--in this case, a running track--barefoot runners experience a shock of only 0.5 to 0.7 times their body weight, whereas shod heel strikers experience 1.5 to two times their body weight--a threefold to fourfold difference.

"I always assumed it was painful and crazy to run barefoot," says a surprised Lieberman. Instead, the findings--published tomorrow in Nature--suggest that going barefoot can reduce the likelihood of pain and damage, because many running injuries, like shin splints and plantar fasciitis, are stress- and impact-induced.

"This is an excellent study," says Dennis Bramble, an evolutionary morphologist at the University of Utah in Salt Lake City. "Heel strikes don't allow you to use these really nifty springs that are unique to human beings, so we're being less efficient than we could be," he says. "It confirms what we should have known all along: We're built to run barefoot."

That confirmation will stoke an ongoing debate. As a glance at this month's Runner's World magazine and a recent book on shoeless running called Born to Run attest, barefoot running has gained a small but devoted following in the past decade, prompting controversy in the running community over whether it is best to run shod or unshod.

So should sporty types shed their shoes and jump on the barefooted bandwagon? "Not at all," says Lieberman. "Shoes are comfortable, and they protect the foot" from glass, asphalt, and other harsh realities of urban running, he notes. Instead, Lieberman (who has since taken up occasional barefoot running himself) recommends a gradual transition for the bare-curious, one that allows the feet and calves to strengthen slowly and avoid injury.