Runner's World Essential Guides by Scott Douglas

Author:Scott Douglas
Language: eng
Format: epub
Publisher: Potter/Ten Speed/Harmony/Rodale
Published: 2011-05-15T04:00:00+00:00

Consider, for example, a study by D. Casey Kerrigan, M.D., et al. that spurred the “Running Shoes Worse than High Heels” headlines. It found that runners experienced greater torques and forces when running in shoes than when running barefoot. This sounds bad. And it might be. Except that no one knows anything about how torques and forces are related to running injuries. It’s all guesswork.

Also, Kerrigan isn’t exactly a disinterested party. She has designed some sort of minimalist running shoe, and stands to profit from an attack on conventional running shoes. The same is also true of Craig Richards, who in 2010 published a widely quoted study challenging shoe companies to produce evidence that their shoes actually prevented injuries. According to Richards, none of their shoes did. Richards has a stake in a minimalist shoe company. I’m not calling Kerrigan and Richards liars. Far from it—I agree with Richards’s conclusion. But we should understand the motivation behind their writing and their research projects.

The other thing to understand about Kerrigan’s study is that she didn’t identify any running injuries. She didn’t even look for them. Instead, she went looking for various torques and forces. This is an entirely reasonable approach, but it doesn’t prove much, for the simple reason that we don’t know how torques and forces relate to injuries. Some forces are bad; you can break a toe if you kick a rock while trail running. But other forces are good; think about what happens to astronauts’ bodies without the force of gravity—their muscles atrophy and bones turn to mush.

The relationship between forces and injuries is, for almost all of us, incomprehensibly complicated. In one amazing study, a researcher asked athletes to jump off a bench onto floor mats that provided different degrees of cushioning. They were told when they were jumping onto a well-cushioned mat and when they were jumping onto a less-cushioned mat. Only this mat story was a complete sham, because all the mats were identical. Nonetheless, the athletes registered more shock forces when told they were jumping onto a well-cushioned mat than a less-cushioned one. Why? According to one hypothesis, the athletes relaxed more (they didn’t “pre-activate” their muscles) when they thought they were headed for a soft landing. As a result, the cushioning increased the forces the athletes experienced rather than decreasing them.

Based on this study, one might predict that Kerrigan’s runners would register greater forces in shoes than barefoot. Obviously, they would expect the shoes to provide cushioning. They would relax. They wouldn’t pre-activate. And the result would be greater forces, not smaller ones.

This is exactly what Kerrigan found in her study. She concluded that conventional running shoes might increase the risk of injuries. I conclude that there are lots of other factors involved.

Kerrigan also reported that barefoot runners adopted a 6 percent shorter stride than shod runners. Common sense tells us they did this to reduce forces. Only Kerrigan says that’s not the case; she used some sort of mathematical analysis to eliminate shorter stride as a factor.

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