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The patterns of activity of 33 forelimb muscles during unrestrained overground stepping in eight adult cats were analysed using intramuscular electromyography. Three general patterns were found. Some muscles began activity during the first extension epoch (E1) and ceased near the end of the third extension epoch (E3) and were considered extensors. Others, considered flexors, began activity just prior to the flexion (F) epoch and ceased at or just after the onset of E1. Other muscles showed a biphasic pattern of activation; one period of activity occurring during F, the other during the extension epochs. In all regions of the limb, individual muscles displayed variation in the onset and time course of activity. The results are interpreted in terms of a model of locomotor generation which proposes specific neural output to individual muscles. Muscles of the shoulder region are proposed to act mainly to produce translatory and rotatory movements of the scapula associated with lengthening the step. Muscles of the elbow region and antebrachium are interpreted as playing roles both in producing flexion-extension movements and in the absorption of energy. The latter group are considered especially suitable to energy absorption because of their pennate arrangement of muscle fasciculi and their long tendons.
Arthur W. English (Sun,) studied this question.