It's a ubiquitous human behavior that's puzzled scientists for years: Why do humans almost always feel the need to swing their arms - the opposite arm from their stepping leg forward - as they walk?

Especially when, scientifically speaking, it appears to be such a wasteful use of energy.

But just try holding your arms to your sides while you take a few strides, said University of Michigan researcher Peter Adamczyk, a co-author of a study designed to get to the bottom of it.

He and co-authors Steven Collins and Arthur Kuo proposed a theory about why arm swinging requires less energy and provides more of a biomechanic advantage than any other alternatives. The results of their study were recently published in the Proceedings of the Royal Society B.

Check out a video of Adamczyk explaining more by clicking on the video below.

Why does this matter?

Some of the applications of the Human Biomechanics and Control Lab at U-M have included finding ways to help stroke or injury patients adapt to gain mobility. Other parts of their research have looked into how elite athletes move or how shoe makers might design a better shoe.

There's been a greater interest in recent years for creating robots for daily tasks, Adamczyk said. Understanding how the human body works could play a role in making them behave in more humanistic ways, Adamczyk said.

Besides, Adamczyk said, "People are interesting."

Tina Reed covers health and environment for AnnAbor.com. Reach her at tinareed@annarbor.com.