Re: Swingers.
For one thing, it is surprisingly small in energy costs, requiring little torque, or rotational twist, from the shoulder muscles.
Holding one's arms as one walks requires 12% more metabolic energy, compared with swinging them.
The arms' pendulum swing also helps dampen the bobbing 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 63%.
Should you prefer to walk with an opposite-to-normal swing, meaning that your right arm moves in sync with your right leg and your left arm is matched to the motion of your left leg, the energy cost of using your shoulder muscles will fall.
The downside, though, is that opposite-to-normal swing forces up the metabolic rate by a quarter.
The study, headed by Dr Steven Collins at the University of Michigan, says we should give the thumb's-up to arm swinging.
"Rather than a facultative relic of the locomotion needs of our quadrupedal ancestors, arm swinging is an integral part of the energy economy of human gait," say the team.
Well you did ask!