RELATIONSHIP BETWEEN ANKLE MUSCLE AND JOINT KINETICS DURING THE STANCE PHASE OF LOCOMOTION IN THE CAT

The purpose of this study was to examine the relationship between inte rnal force production in selected skeletal muscles and the externally calculated joint moment during overground locomotion in the adult cat. Hindlimb segments were modelled as a linked system of rigid bodies an d a generalized muscle moment (GMM), the sum over all active and passi ve tissues acting about the joint, was calculated using principles of inverse dynamics. Moments produced by individual muscles were calculat ed using tendon transducers implanted in freely moving cats and muscle moment arm information. Results indicated that the externally measure d variables of peak ground reaction force and joint position were equa lly important to the determination of peak ankle GMM. Examination of p eak moments revealed that increases in peak ankle GMM were met by incr eases in medial (MG) and lateral (LG) gastrocnemius output. Peak soleu s (SOL) moments did not change significantly as a function of peak ank le GMM. The role of the plantaris (PLT) was less clear, with peak mome nts increasing significantly as a function of peak ankle GMM in one ca t. All four ankle extensors were important to the attainment of peak a nkle GMM early in stance. Subsequently, SOL and PLT contributed substa ntially to the ankle GMM throughout stance, LG moments declined to nea r zero, soon after peak ankle GMM; and MG moments demonstrated a subst antial but more gradual decline. The relative contributions of these i ndividual muscles to the ankle GMM were supported by their respective architecture, uniarticular versus multiarticular function. and physiol ogical profiles.