Donelan J Maxwell, Kram Rodger, Kuo Arthur D
Department of Integrative Biology, University of California, Berkeley, CA 94720-3140, USA.
J Exp Biol. 2002 Dec;205(Pt 23):3717-27. doi: 10.1242/jeb.205.23.3717.
In the single stance phase of walking, center of mass motion resembles that of an inverted pendulum. Theoretically, mechanical work is not necessary for producing the pendular motion, but work is needed to redirect the center of mass velocity from one pendular arc to the next during the transition between steps. A collision model predicts a rate of negative work proportional to the fourth power of step length. Positive work is required to restore the energy lost, potentially exacting a proportional metabolic cost. We tested these predictions with humans (N=9) walking over a range of step lengths (0.4-1.1 m) while keeping step frequency fixed at 1.8 Hz. We measured individual limb external mechanical work using force plates, and metabolic rate using indirect calorimetry. As predicted, average negative and positive external mechanical work rates increased with the fourth power of step length (from 1 W to 38 W; r(2)=0.96). Metabolic rate also increased with the fourth power of step length (from 7 W to 379 W; r(2)=0.95), and linearly with mechanical work rate. Mechanical work for step-to-step transitions, rather than pendular motion itself, appears to be a major determinant of the metabolic cost of walking.
在步行的单支撑阶段，重心运动类似于倒立摆。理论上，产生摆动运动不需要机械功，但在步间转换过程中，需要功来将重心速度从一个摆动弧重定向到下一个摆动弧。一个碰撞模型预测负功的速率与步长的四次方成正比。需要正功来恢复损失的能量，这可能会带来成比例的代谢成本。我们让9名受试者在一系列步长（0.4 - 1.1米）范围内行走，同时将步频固定在1.8赫兹，以此来检验这些预测。我们使用测力板测量单个肢体的外部机械功，并使用间接量热法测量代谢率。正如预测的那样，平均负外部机械功率和正外部机械功率随步长的四次方增加（从1瓦增加到38瓦；r² = 0.96）。代谢率也随步长的四次方增加（从7瓦增加到379瓦；r² = 0.95）并且与机械功率呈线性关系。步间转换的机械功，而非摆动运动本身，似乎是步行代谢成本的主要决定因素。
