While proper running form is no doubt crucial, it turns out you don't need to be so concerned when it comes to your arms.
The most efficient arm swing may be the one that you use naturally, concludes a new study, published last week in The Journal of Experimental Biology. The study, which tested 13 experienced runners, found that efficiency was largely unaffected by differences in arm swing. While all people bent their elbows—and most crossed their arms slightly in front of their chest with each swing—“there was tremendous variation in the normal arm swings” of the volunteers, study author Christopher Arellano, Ph.D., told the New York Times.
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We had our doubts. Can it really be true that our body just knows the best way to pump our arms all on its own? So we consulted a pro: "I agree with that completely," says Michael Joyner, M.D. If you asked a running coach to say who they thought was most efficient among a group of runners based solely on how they look, that wouldn't be an effective strategy, he says. "Sometimes people who look terrible, run well, and are pretty efficient."
Just make sure you are pumping your arms, of course. While this may seem like a no brainer, this study was the first to confirm that swinging your arms does indeed burn less energy than keeping your arms behind your back, across your chest, or on top of your head. (Can you picture that for a moment?)