But although it happens passively, arm swingingplays an important role in making your stridemore efficient. It does this by counterbalancingyour torso and hips and keeping them from twistingand bobbing too much. Holding your arms stillagainst your sides while walking requires twelvepercent more energy than if your arms are allowed toswing naturally. Forcing your arms to swing in syncwith the leg on the same side of your body uses awhopping twenty-six percent more energy thannormal walking. Even when walkers had their armsstrapped to their sides, so no muscle control was required to keep them still, they used sevenpercent more energy than when their arms could swing freely. This suggests that armswinging is not just a passive byproduct of walking, but actually makes walking easier.

尽管挥胳膊是被动发生的，但是挥胳膊在走路中起着很重要的作用。挥胳膊会抵消膝盖和屁股的阀作用，防止它们过度扭曲或挥动。如果走路时你把胳膊放在体侧不动，这比挥动胳膊走路要多消耗百分之十二的能量。如果强迫胳膊和腿向同一方向挥动，会比正常走路多消耗百分之二十六的能量。即使走路时将胳膊绑在体侧，不需要肌肉来保持胳膊不动，也比挥动胳膊是多消耗百分之七的能量。这表明挥动胳膊不是走路的副产品，而是让走路变得更容易。

plays an important role in 在……起重要作用 counterbalance v. 使平衡; 抵消 whopping adj. 巨大的strap vt.(用带子)捆扎 byproduct n. 副产品