The forces and moments internal to the human body may not be directly measured. Therefore, models are developed to estimate these reactions using the principles of rigid-body mechanics. In this study, the Newton-Euler equations of motion were written for rigid-body approximations of the foot, shank and thigh segments of the right lower limb and were solved for the three—dimensional components of the force and moment at the linkage centers of the ankle, knee and hip during stance phase of locomotion. An experimental protocol was also developed to provide the necessary input for the equations of motion. The experimental and analytical techniques available provided three-dimensional position data for targets placed on the limb segments, three-dimensional ground reaction forces and moments, and anthropometric measurements.' The literature was reviewed to predict the directions of the principal axes, the location of the center of mass, the principal moments of inertia and the mass of each segment. A numerical solution technique, based on the method of least squares, was developed to compute the angular velocities and accelerations of the three links.

The forces and moments computed at the linkage centers of the right lower limb compared favorably with those presented in the literature. The choice of coordinate system in which these reactions were expressed was found to have an extreme effect on both the magnitudes and directions of the forces and moments. The static and dynamic components of the resultant forces and moments computed at each of the three joints were determined and their percent contribution to the total was calculated. The dynamic terms were found to provide a minimal contribution at the ankle, but showed a contribution of 0% - 80% of the total force at the knee and hip, and 0% - 50% of the total moment at these two joints. It was concluded that a complete analysis of the forces and moments at the linkage centers of the lower limbs produced during stance phase of locomotion must include the dynamic components of the equations of motion, as well as, the static components.