Have you ever wondered why we swing our arms while walking? It’s a curious phenomenon, since arms don’t play an obvious role in locomotion. You can still walk normally when your arms are full of groceries or with your hands in your pockets, so why do we do it? Isn’t it a waste of energy? Two independent studies, both published in 2009, may provide some answers to this mystery. The Answer… Using a combination of mechanical models, computer simulations and tests with human walkers and runners, the studies concluded that arm swinging just sort of…happens. In other words, you don’t need muscles for your arms to start swinging, although you can use muscles to swing your arms higher or more forcefully. If you’re walking and your arms are hanging relaxed by your sides, they will normally swing in sync with the opposite leg. That is, your right arm swings forward when your left leg steps forward and vice versa.