Determinants of the center of mass trajectory in human walking and running
CR Lee and CT Farley
It happens that about 5 years ago, a fellow by the name of Tad McGeer built some mechanisms, basically legs with knees and hip masses, that walked down shallow slopes with NO CONTROL or actuation. Stability was born from the passive interactions of gravity and inertia, and dissipative collisions at kneestrike and heelstrike. In other words, walking is a "natural mode", if you will, of a set of legs.
Department of Integrative Biology, University of California, Berkeley 94720-3140, USA.
Walking is often modeled as an inverted pendulum system in which the center of mass vaults over the rigid stance limb. Running is modeled as a simple spring-mass system in which the center of mass bounces along on the compliant stance limb. In these models, differences in stance-limb behavior lead to nearly opposite patterns of vertical movements of the center of mass in the two gaits. Our goal was to quantify the importance of stance-limb behavior and other factors in determining the trajectory of the center of mass during walking and running. We collected kinematic and force platform data during human walking and running. Virtual stance-limb compression (i.e. reduction in the distance between the point of foot-ground contact and the center of mass during the first half of the stance phase) was only 26% lower for walking (0.091 m) than for running (0.123 m) at speeds near the gait transition speed. In spite of this relatively small difference, the center of mass moved upwards by 0.031 m during the first half of the stance phase during walking and moved downwards by 0.073 m during the first half of the stance phase during running. The most important reason for this difference was that the stance limb swept through a larger angle during walking (30.4 degrees) than during running (19.2 degrees). We conclude that stance-limb touchdown angle and virtual stance-limb compression both play important roles in determining the trajectory of the center of mass and whether a gait is a walk or a run.
Above is an example of the SPRING LOADED INVERTED PENDULUM MODEL
Look anything like a G.O.L.F.er?