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Abstract
The purpose of this project was to develop mechanical models of a standing and a walking human, and to use these models to identify mechanical principles of postural control. The models represented the human as inverted pendulums of multiple rigid segments, joined at frictionless pin joints, in the sagittal plane. The dynamic equations of motion were solved on a digital computer. A three segment model was used to simulate the standing human. Six segments were used to simulate walking. The movement of the model during the first 80 ms following an imposed disturbance from equilibrium was studied. An iterative approach was used to search for joint torque combinations which could correct for the mechanical disturbance. The movement goal was defined as returning all segments to the original equilibrium position for standing, or maintaining the undisturbed movement trajectory for walking. The models demonstrated a systematic trend in the joint torque combinations which were successful. To counteract a disturbance, the models predicted a certain proportional relationship necessary between the hip, knee and ankle torques. Moreover, their combined effect must result in a net corrective action. The proportional relationship between joint torques is a function of model anthropometry and movement goal; it is independent of disturbance characteristics. The models also predicted that during the early and middle single-support phase of walking, similar joint torque combinations to those used in standing would be effective. The late single-support phase required different combinations.
Experimental validation was carried out for a select number of model predictions. An apparatus capable of generating impulsive force disturbances was designed and constructed. A horizontal force displacing the knee in the forward direction was applied to subjects during standing and walking. Film, force plate and electromyographic data were recorded. The results indicated that subjects responded with joint torques which were consistent with the predictions of the model. All subjects responded with low joint torque values, close to the lowest successful combinations predicted by the model. Subjects differed in the combination of muscles activated, but were consistent within themselves.
