Swing

Why do people swing their arms when they walk? Not exactly a searing question but the answer is interesting, in a modest, yawning, yet green energy ergonomic way.

Yahoo: Out on a limb: Arm-swinging riddle is answered

Holding one's arms as one walks requires 12 percent more metabolic energy, compared with swinging them.

The arms' pendulum swing also helps dampen the bobbly up-and-down motion of walking, which is itself an energy drain for the muscles of the lower legs.

If you hold your arms while walking, this movement, called vertical ground reaction moment, rises by a whopping 63 percent.