The collisional geometry of economical walking predicts human leg and foot segment proportions

Abstract

Human walking appears complicated, with many muscles and joints performing rapidly varying roles over the stride. However, the function of walking is simple: to support body weight as it translates economically. Here, a scenario is proposed for the sequence of joint and muscle actions that achieves this function, with the timing of muscle loading and unloading driven by simple changes in geometry over stance. In the scenario, joints of the legs and feet are sequentially locked, resulting in a vaulting stance phase and three or five rapid ‘mini-vaults’ over a series of ‘virtual legs’ during the step-to-step transition. Collision mechanics indicate that the mechanical work demand is minimized if the changes in the centre-of-mass trajectory over the step-to-step transition are evenly spaced, predicting an even spacing of the virtual legs. The scenario provides a simple account for the work-minimizing mechanisms of joints and muscles in walking, and collision geometry allows leg and foot proportions to be predicted, accounting for the location of the knee halfway down the leg, and the relatively stiff, plantigrade, asymmetric, short-toed human foot.

The functions of leg muscles, structures and mechanisms in running

“…Leg design, joint and muscle action in human running can be viewed as a sequence of geometrically engaged and disengaged linkages, achieving the task of a vehicle-weight support during translation-alongside the demands of an effective machine -mechanical work avoidance and economical work supply. While implications of a compromise between the two demands have been explored quite broadly, accounting for the scaling of posture, bipedal and flapping gaits [14], or have been used to disregard certain potential work avoidance strategies (in human walking; [25]), the linkages described here demonstrate how the two functions can be achieved simultaneously within the same leg, but with different muscle actions, without compromising each other.…”

Modeling and Analysis of Foot Function in Human Gait Using a Two-Degrees-of-Freedom Inverted Pendulum Model with an Arced Foot

“…The human foot structure has the structure suitable for bipedal walking. As shown in Figure 1C, the ankle joint is located approximately a quarter of the foot length from the heel [48,49]. Humans can progress forward effectively by using the foot functions of heel-rocker, anklerocker, forefoot-rocker, and toe-rocker, which produce a wheel-like rolling motion under the foot [50].…”