Actions of FDL and FHL muscles in intact cats: functional dissociation between anatomical synergists.

Abstract

The electromyographic (EMG) activity, force production and length changes of the flexor digitorum longus (FDL) muscle in normal cats were examined during treadmill locomotion, jumping, postural adjustments, and scratch and paw-shake reflexes, by using chronically implanted transducers and electrodes. EMG activities in its anatomical synergist, flexor hallucis longus (FHL), and a number of other hindlimb muscles were recorded simultaneously, and videotapes were made of the animals'' movements. The FDL and FHL muscles are strict anatomical synergists, but their activity patterns in normal movements are quite dissimilar, especially in locomotion. FDL action is complex and unique among the muscles studied, including elements of stereotyped flexor and facultative extensor function. FHL action is simply that of an antigravity extensor, resembling the ankle extensor muscles, gasdtrocnemius and soleus.