You can do it, but it takes some concentration. And it feels weird. At least, it does to me.
Why am I even bringing this up? Walking from my office to the subway this evening, I decided to see if I could walk without swinging my arms. (My iPhone was low on juice and I had to amuse myself somehow. Plus a speedwalker had just nearly knocked into me, her arms swinging in wide arcs back and forth.)
I found that I could do it as long as I concentrated on keeping them still; if my mind wandered, my arms started to swing again.
And keeping them still just felt…uncomfortable. Not painful or stiff, but odd. Unnatural. After a couple of minutes, I wanted viscerally to let them swing again.
Over dinner, I asked the family why they thought we swing our arms when we walk. My wife thought it had something to do with keeping balance. My older son thought it was a holdover from our ape ancestors who walk on all fours; my younger thought it was because our ape ancestors swung from trees.
My guess? I was on board with the balance thing, thinking that it was a way of compensating for not having tails.
Keep swinging, baby
The answer, according to a 2010 story on Indiana Public Media’s Moment of Science, is that arm swing does have something to do with balancing, but not in the way I or my family were thinking of it:
[A]rm swinging [makes] your stride more efficient. It does this by counterbalancing your torso and hips and keeping them from twisting and bobbing too much.
Their explanation, based on a pair of 2009 studies, is that by counterbalancing the motion of our stride, we keep our gait more efficient. According to Moment of Science, the studies point out that holding your arms still uses 12 percent more energy than letting them swing freely.
Where you really pay a price is if you try to swing your arms in sync with your walk (e.g., swing your right arm forward when you step forward with your right leg):
Forcing your arms to swing in sync with the leg on the same side of your body uses a whopping twenty-six percent more energy than normal walking.
It makes sense when you think about it. When you step forward with one leg, you’re generating a lot of torque and twisting your body. Swinging the opposite arm forward at the same time cancels that torque out.
Passive dynamic, not passive aggressive
“Instead of being muscle-driven, arm swinging appears to arise from the natural dynamics, or passive dynamics, of the body as it walks.”
Collins first got interested in the mechanics of arm swinging while studying the gait of simple robots he called “passive dynamic machines,” capable of walking down an incline powered only by gravity. (He was using them to test ideas about human and robot locomotion.)
Without arms, the machines tended to spin out. But in robots with freely swinging arms, the arms swung back and forth in sync with the robot’s opposite leg, just like people. His follow-up studies of the mechanics of arms swinging using human volunteers led to his 2009 paper.
If nothing else, Collins squashed my kids’ theories about arm swinging and ancestral apes. Again from Cosmos:
“This puts to rest the theory that arm swinging is a vestigial relic from our quadrupedal ancestors.”
They’ll be so disappointed.