Structure and Motion Laboratory, The Royal Veterinary College, University of London, North Mymms, Hatfield, Herts AL9 7TA, UK.
J R Soc Interface. 2012 Aug 7;9(73):2011-5. doi: 10.1098/rsif.2012.0145. Epub 2012 Apr 4.
Bipedal animals experience ground reaction forces (GRFs) that pass close to the centre of mass (CoM) throughout stance, first decelerating the body, then re-accelerating it during the second half of stance. This results in fluctuations in kinetic energy, requiring mechanical work from the muscles. However, here we show analytically that, in extreme cases (with a very large body pitch moment of inertia), continuous alignment of the GRF through the CoM requires greater mechanical work than a maintained vertical force; we show numerically that GRFs passing between CoM and vertical throughout stance are energetically favourable under realistic conditions; and demonstrate that the magnitude, if not the precise form, of actual CoM-torque profiles in running is broadly consistent with simple mechanical work minimization for humans with appropriate pitch moment of inertia. While the potential energetic savings of CoM-torque support strategies are small (a few per cent) over the range of human running, their importance increases dramatically at high speeds and stance angles. Fast, compliant runners or hoppers would benefit considerably from GRFs more vertical than the zero-CoM-torque strategy, especially with bodies of high pitch moment of inertia--suggesting a novel advantage to kangaroos of their peculiar long-head/long-tail structure.
两足动物在整个支撑阶段都会经历地面反作用力（GRF），这些力靠近质心（CoM），首先使身体减速，然后在支撑阶段的后半段重新加速。这导致动能的波动，需要肌肉产生机械功。然而，在这里我们分析表明，在极端情况下（具有非常大的身体俯仰惯性矩），通过 CoM 连续对齐 GRF 需要比维持垂直力更大的机械功；我们通过数值计算表明，在实际条件下，GRF 在整个支撑阶段通过 CoM 和垂直方向传递是能量有利的；并证明，在具有适当俯仰惯性矩的人类中，实际 CoM 扭矩曲线的幅度，如果不是精确的形式，则大致符合简单的机械功最小化。虽然 CoM 扭矩支持策略在人类跑步范围内的潜在能量节省很小（百分之几），但在高速和支撑角度下，它们的重要性会急剧增加。快速、灵活的跑步者或跳跃者将从比零 CoM 扭矩策略更垂直的 GRF 中受益匪浅，尤其是在具有高俯仰惯性矩的身体中——这表明袋鼠独特的长头/长尾结构具有新的优势。
