Takin' a break from weighty science research like finding a cure for cancer and whatnot, scientists have now solved the riddle of why we swing our arms when walking:
Swinging one's arms comes at a cost. We need muscles to do it, and we need to provide energy in the form of food for those muscles. So what's the advantage?
Little or none, some experts have said, contending that arm-swinging, like our appendix, is an evolutionary relic from when we used to go about on all fours.
But a trio of specialists from the United States and the Netherlands have put the question to rigorous tests.
They built a mechanical model to get an idea of the dynamics of arm-swinging and then recruited 10 volunteers, who were asked to walk with a normal swing, an opposite-to-normal swing, with their arms folded or held by their sides. [...]
Arm-swinging turned out to be a plus, rather than a negative, the investigators found.
For one thing, it is surprisingly, er, "'armless" in energy costs, requiring little torque, or rotational twist, from the shoulder muscles. Holding one's arms as one walks requires 12 percent more metabolic energy, compared with swinging them.