THE INTERPRETATION OF MEDIO-LATERAL REACTION FORCES IN HUMAN LOCOMOTION USING BODY COORDINATE SYSTEMS

The research work reported in this dissertation focuses on the mathematical interpretation of force plate measurements for normal and abnormal locomotion. A force plate large enough (approximately 16 sq. ft. in area) to accommodate many types of abnormal gait normally encountered by the clinician, was developed. The force plate was sufficiently sensitive to ground-reaction force measurements in all the three principal directions of motion to allow the measurements of the subtle changes in ground-reactions as a result of injury to any of the supporting limbs.

A simple three dimensional model is proposed in order to interpret the significance of reaction parameters. The model input, in the form of displacement patterns of limb segments and ground-reaction forces were obtained using bi-plane photography and force plate measurements respectively. The mathematical model proposed relates the dynamics of upper body motion to those of the lower extremity in support phase. A set of symmetry parameters highly indicative of gait disruption have been defined. The parameters of symmetry which relate reaction forces as measured by the force plate to asymmetrical characteristics of pathological gait have not been previously defined in the literature.

The present work relates the measured reaction force patterns to the upper body motions using the principle of impulse and momentum and force and moment equilibrium. In the majority of investigations on gait analysis the moments and forces at various limb joints have been expressed in the general reference frame. In the present study, movements of the segments are related to the angular rotations of the body fixed coordinate system. Special coordinate transformation techniques have been proposed and are general enough to accept the large angular rotations characteristic of pathological gait. The moments in the moving upper body coordinate system are then related to ground-reaction forces through the parameters developed. In this way, the compensatory maneuver brought about by the upper body in the event of injury to one of the supporting members is better understood and quantified.