Tread Lightly.

AuthorPowell, Alvin
PositionSPORTS SCENE

AS EVIDENCE HAS MOUNTED that distance running is not just a natural human activity enjoyed by millions, but one that played a key role in evolution, a puzzle has emerged. Why, if humans are so well adapted to running long distances, do runners get hurt so often? A study out of Harvard Medical School and the National Running Center at Harvard-affiliated Spaulding Rehabilitation Hospital provides a puzzle piece, linking injury to the pounding runners' bones take with each step. The work, led by Irene Davis, director of Spaulding and visiting professor of physical medicine and rehabilitation, found that a group of runners who never had been hurt landed each footfall more softly than a group who had been injured badly enough to seek medical attention.

Statistics on such injuries can vary widely, but somewhere between 30%75% of runners are hurt annually, a number that has led researchers to investigate a wide array of possible explanations, from modern running shoes to stretching, running frequency, weight, bio mechanical misalignment, and muscle imbalance.

A 2012 Harvard study, for example, zeroed in on injury rates among track and cross-country athletes who land on the forefoot versus the heel. Researchers--led by Daniel Lieber-man, the Edwin M. Lerner II Professor of Biological Sciences and chair of the Department of Human Evolutionary Biology--were probing the idea that, before the advent of cushioned running shoes, most runners landed on the ball of the foot because landing on the heel would be too painful. Landing on the forefoot allows the foot and ankle to absorb some of the landing shock, an impact that today's running shoes cannot completely erase for those who land on their heels.

With most runners being heel-strikers today, the added shock, multiplied over thousands of footsteps, could explain high injury rates. The 2012 study added fuel to the debate, finding a two-to-one difference in repetitive stress injuries between heel- and forefoot-strikers. Davis' research, meanwhile, focuses on heel-strikers exclusively, since they make up most of today's runners, and examines a cohort seldom studied, partly because they are pretty rare: those who never have been injured. "We can learn a lot from that group," she says. "What are they doing right?"

Davis and colleagues recruited 249 female recreational athletes who each ran at least 20 miles a week. They investigated the participants' strides by having them run over a force plate that...

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