Adamczyk Peter G, Collins Steven H, Kuo Arthur D
Department of Mechanical Engineering, University of Michigan, Ann Arbor, MI 48109-2125, USA.
J Exp Biol. 2006 Oct;209(Pt 20):3953-63. doi: 10.1242/jeb.02455.
The plantigrade human foot rolls over the ground during each walking step, roughly analogous to a wheel. The center of pressure progresses on the ground like a wheel of radius 0.3 L (leg length). We examined the effect of varying foot curvature on the mechanics and energetics of walking. We controlled curvature by attaching rigid arc shapes of various radii to the bottoms of rigid boots restricting ankle motion. We measured mechanical work performed on the center of mass (COM), and net metabolic rate, in human subjects (N=10) walking with seven arc radii from 0.02-0.40 m. Simple models of dynamic walking predict that redirection of COM velocity requires step-to-step transition work, decreasing quadratically with arc radius. Metabolic cost would be expected to change in proportion to mechanical work. We measured the average rate of negative work performed on the COM, and found that it followed the trend well (r2=0.95), with 2.37 times as much work for small radii as for large. Net metabolic rate (subtracting quiet standing) also decreased with increasing arc radius to a minimum at 0.3 L, with a slight increase thereafter. Maximum net metabolic rate was 6.25 W kg(-1) (for small-radius arc feet), about 59% greater than the minimum rate of 3.93 W kg(-1), which in turn was about 45% greater than the rate in normal walking. Metabolic rate was fit reasonably well (r2=0.86) by a quadratic curve, but exceeded that expected from COM work for extreme arc sizes. Other factors appear to increase metabolic cost for walking on very small and very large arc feet. These factors may include effort expended to stabilize the joints (especially the knee) or to maintain balance. Rolling feet with curvature 0.3 L appear energetically advantageous for plantigrade walking, partially due to decreased work for step-to-step transitions.
在每一步行走过程中，人类的足底在地面上滚动，大致类似于一个轮子。压力中心在地面上的移动方式类似于半径为0.3L（腿长）的轮子。我们研究了改变足部曲率对行走力学和能量学的影响。我们通过将不同半径的刚性弧形连接到限制踝关节运动的刚性靴子底部来控制曲率。我们测量了10名人类受试者在穿着七种半径从0.02 - 0.40米的弧形装置行走时，对质心（COM）所做的机械功以及净代谢率。动态行走的简单模型预测，质心速度的重新定向需要步间转换功，该功随弧形半径呈二次方减少。代谢成本预计会与机械功成比例变化。我们测量了对质心所做的负功的平均速率，发现其与预测趋势吻合良好（r2 = 0.95），小半径弧形装置所做的功是大半径的2.37倍。净代谢率（减去安静站立时的代谢率）也随着弧形半径的增加而降低，在0.3L时达到最小值，此后略有增加。最大净代谢率为6.25W kg(-1)（对于小半径弧形足部），比最小速率3.93W kg(-1)大约高59%，而最小速率又比正常行走时的速率大约高45%。代谢率通过二次曲线拟合得相当好（r2 = 0.86），但对于极端弧形尺寸，其代谢率超过了由质心功所预期的值。其他因素似乎会增加在非常小和非常大弧形足部上行走的代谢成本。这些因素可能包括为稳定关节（特别是膝盖）或维持平衡所花费的努力。曲率为0.3L的滚动足部在足底行走中似乎在能量方面具有优势，部分原因是步间转换的功减少。
