You probably think that running is a leg thing. And yes, your lower half does most of the work. But new research suggests that arm movements are equally important to running form — and that swinging your arms can affect the ease with which you run.

OK, so pumping your arms feels like it takes more effort than, say, crossing them or letting them hang out along your sides. And yes, swinging them while you run does require some muscle power to keep your elbows bent and arms in motion. But when researchers from University of Colorado and Brown University assessed different running positions (hands above the head, arms across the chest, and arms behind the back) they found that arm swinging uses less energy and actually makes running much easier — even though it means moving your limbs more.

That's because swinging the arms helps counterbalance swinging legs, says lead study author Christopher Arellano, Ph.D., a National Institutes of Health post-doctoral fellow at Brown University. Without arm movement, you have to rotate your torso every time you take a step to counteract the movement of your legs. All that twisting takes up even more energy than swinging your arms, tiring you out faster. (And P.S., it looks mighty awkward.)

The study did find that running without any arm movement (i.e., with your hands on top of your head) could burn about 13 percent more calories than running regularly. But (and it's a big one) that doesn't mean you should do it. Stop swinging, and you could risk spine injury that makes it difficult to run at all, says Arellano, who adds that the best way to burn more calories while you run is to (duh) run for longer.

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