The Human Body and Bipedal Walking

In human bipedal walking, body segments act in harmony with each other. However, both the human body and bipedal walking are unique among other primates and other terrestrial animals. Therefore, some explanation must be offered for this uniqueness. It seems correct to state that there are some mechanical relationships between the human body and bipedal walking. Body motions are achieved by opposing muscular efforts against gravitational force, but basic daily motions such as walking should be performed to minimize energy consumption. One feasible solution which minimizes muscle effort is the coinciding of the motion pattern with the vibration mode of the system. In this study, bipedal walking was mathematically modeled as a coupled vibration system of body segments. The mathematical model was a three-dimensional model with the following components: head, thorax, pelvis, arms, thighs, shanks and feet. A spring and a dashpot are attached against the relative rotation between thorax and pelvis, and also between thigh and shank. The spring element of the knee joint was a nonlinear spring to avoid hyper-extension. Sagittal and vertical forces at the pelvis segments, and moments at the waist and hip joints were applied as external forces. Accordingly, the vibrations of body segments were expressed by a 10th simultaneous second-order differential equation. The numerical calculation was performed using the 4th order Runge-Kutta method. The vibration mode of the experimental link model was measured by a 16mm cine camera. The experimental results agreed with the results calculated from the same morphological constants of the link model. As a result, the following close relationships between the human body and bipedal walking were found: (1) adequate viscoelasiticity at the waist joint is required for effective walking, (2) human morphological body balance is matched for smooth and harmonious bipedal walking. The method of this study will be able to be utilized for the evaluation of artificial legs or the estimation of the effects of orthopedic operations.