THE DISTAL HINDLIMB MUSCULATURE OF THE CAT - MULTIAXIS MOMENT ARMS ATTHE ANKLE JOINT

The cat hindlimb muscles have been classified, traditionally, as flexo rs and extensors, based on their actions in the parasagittal plane and their patterns of recruitment during locomotion and reflex responses. This study provides a detailed examination of the relative magnitudes of the various moment arms of the cat ankle muscles and the interdepe ndent effects of position in the various axes of motion. We used a met hod based on observing small sliding movements of tendon in response t o small angular displacements of the joint. Surprisingly, we found tha t the ankle joint of the cat permits substantial motion in three axes (eversion/inversion and abduction/adduction as well as extension/flexi on) and many muscles crossing the ankle joint have their largest momen t arms about axes other than extension/flexion. These moment arms ofte n depended on the joint position in the axis of the moment arm and, to a lesser degree, on the extension flexion angle as well. For some mus cles (notably peroneus longus) there was sufficient variability that t he predominant action in neutral posture (axis with the largest moment arm) could change from animal to animal, which may be related to hete rogeneities of locomotor and reflex recruitment reported in the compan ion paper.