Arm Swing and Running Economy

Around the time I started running, I happened to be reading James Joyce’s Portrait of the Artist as a Young Man, in which Mike Flynn, running coach to “some of the best runners of modern times,” instructs young Stephen to run with “his head high lifted, his knees well lifted and his hands held straight down by his sides.” I tried it; it was comically hard.

I mention this because there’s a new paper in the Journal of Experimental Biology from University of Colorado, U.S., researcher Rodger Kram and his former Ph.D. student Chris Arellano (now at Brown University, U.S.) looking into the enduringly confusing topic of what we do with our arms while running, and why. The study compared four different running postures: “normal,” holding the hands behind the back, holding the arms across the chest, and holding the hands on top of the head. The main question they asked was: is swinging your arms while running worthwhile for saving energy and optimising biomechanics?

The answer may seem obvious, but previous studies using various types of “arm-restricted” running have produced conflicting results. That’s why Kram and Arellano decided to test four different running styles, all under the same conditions. The results: running with a normal arm swing did indeed burn less energy (3% less than the behind-the-back form, 9% less than across-the-chest, and 13% less than hands-on-head). It also significantly reduced shoulder and pelvis rotation. Those two findings are connected: at least part of the extra energy needed for the “funny runs” probably comes from the muscular effort required to rotate the torso in order to counterbalance the rotational angular momentum of the legs (which is what the arm swing normally does).

The experiment answers some questions, but leaves others open. For example, would you be more efficient if you cut your arms off? As Kram and Arellano point out in the paper, your arms comprise about 10% of your total weight, so getting rid of them would save about 10% of the energy you’d normally burn running. But then you’d have to spend extra energy rotating your torso with each stride, which might outweigh the benefits. A study of Paralympic athletes with no arms, they note, could offer further interesting insights into the role of the arm swing.

Another point they raise in the discussion is the possibility that arms play a different role in sprinting versus distance running. In distance running, the primary goal is to burn as little energy as possible at a given pace, so the best advice seems to be to keep your arms relaxed and let them swing as passively as possible. In sprinting, you want to propel yourself forward as quickly as possible, and you don’t care how much energy you burn, so perhaps there’s a role for pumping your arms actively.

There’s also some neat research suggesting that arm and leg motion is “neurocoupled,” perhaps an evolutionary remnant of when our ancestors were quadrupeds. Gait rehabilitation studies have shown that people are able to generate more force with their legs when they also engage their opposite arms. As Arellano noted in an email when I asked him about this, “this action may provide an ‘indirect’ method to help activate the legs when ‘directly’ activating the legs is compromised, maybe during the period of time when the runner’s legs are fatigued at the end of the race.” Or maybe not – it’s an idea that hasn’t been tested, but would be neat to see studied.

The big conclusion? Keep swinging your arms. How? “I think the ideal scenario for swinging the arms is that the motion would be primarily passive, to help reduce the metabolic cost of running,” Arellano said in his email. So keep them relaxed, in a comfortable position – and not pinned to your sides.


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