英语时差：走路时为什么要摆手？2

But although it happens passively, arm swinging plays an important role in making your stride more efficient. It does this by counterbalancing your torso and hips and keeping them from twisting and bobbing too much. Holding your arms still against your sides while walking requires twelve percent more energy than if your arms are allowed to swing naturally. Forcing your arms to swing in sync with the leg on the same side of your body uses a whopping twenty-six percent more energy than normal walking. Even when walkers had their arms strapped to their sides, so no muscle control was required to keep them still, they used seven percent more energy than when their arms could swing freely. This suggests that arm swinging is not just a passive byproduct of walking, but actually makes walking easier.