McMahon T A, Valiant G, Frederick E C
J Appl Physiol (1985). 1987 Jun;62(6):2326-37. doi: 10.1152/jappl.1987.62.6.2326.
An important determinant of the mechanics of running is the effective vertical stiffness of the body. This stiffness increases with running speed. At any one speed, the stiffness may be reduced in a controlled fashion by running with the knees bent more than usual. In a series of experiments, subjects ran in both normal and flexed postures on a treadmill. In other experiments, they ran down a runway and over a force platform. Results show that running with the knees bent reduces the effective vertical stiffness and diminishes the transmission of mechanical shock from the foot to the skull but requires an increase of as much as 50% in the rate of O2 consumption. A new dimensionless parameter (u omega 0/g) is introduced to distinguish between hard and soft running modes. Here, omega 0 is the natural frequency of a mass-spring system representing the body, g is gravity, and u is the vertical landing velocity. In normal running, this parameter is near unity, but in deep-flexed running, where the aerial phase of the stride cycle almost disappears, u omega 0/g approaches zero.
跑步力学的一个重要决定因素是身体的有效垂直刚度。这种刚度会随着跑步速度的增加而增大。在任何给定速度下，通过比平常更弯曲膝盖的方式跑步，可以有控制地降低刚度。在一系列实验中，受试者在跑步机上以正常姿势和弯曲姿势跑步。在其他实验中，他们沿着跑道跑过一个测力平台。结果表明，弯曲膝盖跑步会降低有效垂直刚度，并减少从脚部到颅骨的机械冲击传递，但需要将氧气消耗率提高多达50%。引入了一个新的无量纲参数（uω0/g）来区分硬跑步模式和软跑步模式。这里，ω0是代表身体的质量 - 弹簧系统的固有频率，g是重力，u是垂直着地速度。在正常跑步中，这个参数接近1，但在深度弯曲跑步中，步幅周期的腾空阶段几乎消失，uω0/g接近0。
