AGONIST AND ANTAGONIST EMG ACTIVATION DURING ISOMETRIC TORQUE DEVELOPMENT AT THE ELBOW IN SPASTIC HEMIPARESIS

Voluntary isometric step contractions of the elbow flexor and extensor muscles were studied in a group of patients with paresis arising as t he result of unilateral cerebral lesion and in a control group of norm al subjects. For each subject the maximum isometric torque in flexion and extension was obtained, along with a series of graduated torque st eps up to this maximum, in order to perform a regression analysis betw een torque developed and the associated agonist and antagonist EMG. Th is relationship proved to be linear in all normal subjects and in all but the most paretic spastic patients. If the patients were grouped ac cording to their ability to make discrete large angle flexion and exte nsion movements at the elbow, a clear correspondence was seen between increasing movement disability and the degree of paresis. No significa nt differences were found in the torque/EMG relationship of spastic pa tients when either elbow extensors or flexors were acting as the agoni st in a contraction. Similarly, no evidence of exaggerated antagonist co-activation was found. It is concluded that, in the upper arm muscle s, hemiparesis following stroke cannot, under isometric conditions, be attributed to hyperactivity of antagonist muscles.