The Distal Hindlimb Musculature of the Cat. Patterns of Normal Use

Chronic recordings were made of electromyographic (EMG) activity, tension, and length of distal hindlimb muscles in six cats performing a variety of normal motor tasks. Muscles studied thoroughly or in part were medial gastrocnemius, lateral gastrocnemius, plantaris, soleus, flexor digitorum brevis, flexor digitorum longus, flexor hallucis longus, tibialis posterior, tibialis anterior, extensor digitorum longus, peroneus longus, and peroneus brevis. Postural and locomotor activities were examined, as well as jumping, landing, scratching, and paw shaking. In general, muscles could be assigned to traditional groupings (e.g. extensor, flexor) related to the demands of the motor task. Patterns of muscle activity were most often consistent with current understanding of muscle mechanics and neural coordination. However, purely functional distinctions between flexor digitorum longus and flexor hallucis longus ("anatomical synergists") were made on the basis of activity patterns. Likewise, the activity of plantaris and flexor digitorum brevis, which are attached in series, was differentiated in certain tasks. The rhythmical oscillatory patterns of scratching and paw shaking were found to differ temporally in a manner consistent with the limb mechanics. In several cases, mechanical explanations of specific muscle activity required length and force records, as well as EMG patterns. Future efforts to study motor patterns should incorporate information about the relationships between muscle activation, tension, length and velocity.