What Determines the Vertical Displacement of the Body during Normal Walking?

Conventional wisdom states that the vertical excursion of the body is reduced by several of six "determinants" of gait to minimize the energy expenditure of walking. However, we have shown that pelvic obliquity and stance-phase knee flexion - the second and third determinants of gait - have little or no effect on the magnitude of the body's vertical excursion during normal walking because the timing of these actions is wrong for reduction of vertical movement to occur. We believe that stance-phase knee flexion and pelvic obliquity provide shock absorption in normal walking during the loading response phase of gait. Our data show that for a given individual the vertical displacement of the body is determined by effective leg length, foot rocker radius, and step length. Using a rocker-based inverted pendulum model of walking, we have derived equations relating walking parameters such as the vertical excursion, step length, cadence, and walking speed. Results from our theoretical analysis compared favorably with actual measurements from able-bodied ambulators walking across a range of speeds from about 0.8 to 2.0 m/sec. We believe that some pathological gaits may be improved through modification of the foot rocker shape and by making adequate provisions for shock absorption.