STANDING SWAY - ITERATIVE ESTIMATION OF THE KINEMATICS AND DYNAMICS OF THE LOWER-EXTREMITIES FROM FORCE-PLATE MEASUREMENTS

In this study, a model for the estimation of the dynamics of the lower extremities in standing sway from force plate data only is presented. A three-dimensional, five-segment, four-joint model of the human body was used to describe postural standing sway dynamics. Force-plate dat a of the reactive forces and centers of pressure were measured bilater ally. By applying the equations of motion to these data, the transvers al trajectory of the center of gravity (CG) of the body was resolved i n the sagittal and coronal planes. An inverse kinematics algorithm was used to evaluate the kinematics of the body segments. The dynamics of the segments was then resolved by using the Newton-Euler equations, a nd the model's estimated dynamic quantities of the distal segments wer e compared with those actually measured. Differences between model and measured dynamics were calculated and minimized, using an iterative a lgorithm to re-estimate joint positioning and anthropometric propertie s. The above method was tested with a group of 11 able-bodied subjects , and the results indicated that the relative errors obtained in the f inal iteration were of the same order of magnitude as those reported f or closed loop problems involved in direct kinematics measurements of human gait.