Movement patterns, biomechanics, and performance characteristics of one-legged standin

There were three primary purposes to this study: (1) to describe the movement patterns of standing on one leg, (2) to study the biomechanics of one legged standing, and (3) to determine performance characteristics of standing on one leg. These goals were accomplished through three-dimensional videography and stabilographic analysis. The main focus of the first goal was to differentiate balance techniques during instances of extreme ankle displacement versus periods of non-extreme ankle displacement. Two primary variables were examined, the ankle joint moment and the moment of the horizontal ankle joint reaction force about the whole body center of mass. The ankle joint moment was of similar magnitude during extreme and non-extreme ankle instances. The moment due to the joint reaction force, however, was over 4 times larger during instances of extreme ankle displacement, than during periods of non-extreme ankle displacement. Thus, two different techniques are used to maintain balance during one legged standing. The ankle torque technique involves a large restorative moment at a stationary ankle joint for balance maintenance, similar to a simple inverted pendulum. The ankle force technique involves a large horizontal force at a moving ankle joint for balance maintenance. During extreme instances, a combination of both techniques was used to maintain balance. During non-extreme periods, balance was maintained primarily through the ankle torque technique.;The main focus of the biomechanical analysis was to examine the role of mechanical stiffness in balance maintenance during one legged standing. The results indicated that mechanical stiffness contributes to balance maintenance. Generally, higher contribution of mechanical stiffness to balance maintenance were observed for the more challenging tasks.;Lastly, normative performance characteristics of one legged standing were determined. Generally, the subjects stood on a slightly flexed knee, with the COP and horizontal projection of the gravity line positioned solidly under the middle of the supporting foot. The orientation of the supporting foot, did not effect the direction of body sway. Thus, body sway results from the motions of the many joints in the human kinematic chain, as opposed to motion solely of the ankle joint.