Structure and Motion Laboratory, The Royal Veterinary College, North Mymms, Hatfield, Herts AL9 7TA, UK.
J R Soc Interface. 2012 Oct 7;9(75):2396-402. doi: 10.1098/rsif.2012.0179. Epub 2012 May 9.
Mechanically, the most economical gait for slow bipedal locomotion requires walking as an 'inverted pendulum', with: I, an impulsive, energy-dissipating leg compression at the beginning of stance; II, a stiff-limbed vault; and III, an impulsive, powering push-off at the end of stance. The characteristic 'M'-shaped vertical ground reaction forces of walking in humans reflect this impulse-vault-impulse strategy. Humans achieve this gait by dissipating energy during the heel-to-sole transition in early stance, approximately stiff-limbed, flat-footed vaulting over midstance and ankle plantarflexion (powering the toes down) in late stance. Here, we show that the 'M'-shaped walking ground reaction force profile does not require the plantigrade human foot or heel-sole-toe stance; it is maintained in tip-toe and high-heel walking as well as in ostriches. However, the unusual, stiff, human foot structure--with ground-contacting heel behind ankle and toes in front--enables both mechanically economical inverted pendular walking and physiologically economical muscle loading, by producing extreme changes in mechanical advantage between muscles and ground reaction forces. With a human foot, and heel-sole-toe strategy during stance, the shin muscles that dissipate energy, or calf muscles that power the push-off, need not be loaded at all--largely avoiding the 'cost of muscle force'--during the passive vaulting phase.
从力学角度来看，对于缓慢的两足运动来说，最经济的步态是将行走视为“倒立摆”，具有以下三个特征：I. 在支撑期开始时，腿部进行冲动性、耗能的压缩；II. 刚性腿部的跳跃；III. 在支撑期末进行冲动性、发力的蹬离。人类行走的特征性“M”形垂直地面反作用力反映了这种冲动-跳跃-冲动策略。人类通过在支撑早期的脚跟到脚掌过渡期间耗散能量来实现这种步态，大约在支撑中期和脚踝跖屈（将脚趾向下推）时以刚性、平足跳跃，在支撑末期进行发力蹬离。在这里，我们表明“M”形行走地面反作用力曲线不需要跖行足或脚跟-脚掌-脚趾支撑；它在踮脚行走和高跟鞋行走以及鸵鸟中都得到维持。然而，人类独特的、僵硬的足部结构——脚跟在脚踝后面，脚趾在前面——通过在肌肉和地面反作用力之间产生机械优势的极端变化，使机械经济的倒立摆行走和生理经济的肌肉负荷得以实现。对于人类足部和脚跟-脚掌-脚趾策略，在支撑期期间，耗散能量的小腿肌肉或发力蹬离的小腿肌肉根本不需要加载——在被动跳跃阶段，在很大程度上避免了“肌肉力量的成本”。
