你是否思考过为什么走路时会摆臂，而且不是同手同脚？
摆臂看起来是一个“成本昂贵”的习惯，它不仅需要肩部运动，而且浪费力气。但是一项最新研究成果显示，行走时摆臂可以让你更省力，也让行走更有效率。
为解开行走摆臂之谜，美国和荷兰的3名研究人员招募10名志愿者，让他们行走时使用不同的摆臂方式，如同手同脚、手臂静止不动和正常的摆臂方式。研究人员测量不同摆臂方式所需的能量，即新陈代谢率和肩部运动所需力量。
结果显示，无论何种摆臂方式只需少量肩部运动，但各自能量消耗差别较大。
研究报告29日发表在英国皇家学会的《皇家学会生物学分会学报》上。
研究负责人、美国芝加哥大学生物力学专家史蒂文·柯林斯介绍说，保持手臂静止不动行走时比正常行走时的代谢率高12％，相当于其他条件相同时行走速度加快20％或行走时身背重10千克的背包。
他在接受《宇宙杂志》采访时说：“摆臂并非受肩膀运动驱使，而是受人们行走时身体的自然动力驱使。”
同样是摆臂，同手同脚的摆臂方式和“钟摆式”摆臂，即正常的摆臂方式对行走的影响大不相同。
研究人员发现，若强行以同手同脚的方式摆臂，步行者就得让脚花费两倍的力量防止身体旋转。
“当你跨出一步时，你的身体实际上正围绕一根竖轴旋转……就像芭蕾女演员跳舞那样，”柯林斯解释说。
研究发现，“钟摆式”摆臂可以抵消驱使身体旋转的力，帮助分担脚的一部分负担。而同手同脚走路时，驱使身体旋转的力量翻倍，意味着步行者的脚得花两倍的力量让身体保持平衡。在这个过程中，新陈代谢率随之上升25％。 （生物谷Bioon.com）
生物谷推荐原始出处：
Proc. R. Soc. B July 29, 2009, doi: 10.1098/rspb.2009.0664
Dynamic arm swinging in human walking
Steven H. Collins1,2,3,*, Peter G. Adamczyk1,2 and Arthur D. Kuo1,2
1Department of Mechanical Engineering, University of Michigan, Ann Arbor, MI 48109-2125, USA
2Department of Biomedical Engineering, University of Michigan, Ann Arbor, MI 48109-2125, USA
3Department of Biomechanical Engineering, Delft University of Technology, NL-2628 CD Delft, The Netherlands
Humans tend to swing their arms when they walk, a curious behaviour since the arms play no obvious role in bipedal gait. It might be costly to use muscles to swing the arms, and it is unclear whether potential benefits elsewhere in the body would justify such costs. To examine these costs and benefits, we developed a passive dynamic walking model with free-swinging arms. Even with no torques driving the arms or legs, the model produced walking gaits with arm swinging similar to humans. Passive gaits with arm phasing opposite to normal were also found, but these induced a much greater reaction moment from the ground, which could require muscular effort in humans. We therefore hypothesized that the reduction of this moment may explain the physiological benefit of arm swinging. Experimental measurements of humans (n = 10) showed that normal arm swinging required minimal shoulder torque, while volitionally holding the arms still required 12 per cent more metabolic energy. Among measures of gait mechanics, vertical ground reaction moment was most affected by arm swinging and increased by 63 per cent without it. Walking with opposite-to-normal arm phasing required minimal shoulder effort but magnified the ground reaction moment, causing metabolic rate to increase by 26 per cent. Passive dynamics appear to make arm swinging easy, while indirect benefits from reduced vertical moments make it worthwhile overall.
