Alteration in the Force and Fatigability of Skeletal Muscle in Quadriplegic Humans Following Exercise Induced by Chronic Electrical Stimulation

Abstract

The paralyzed forearm finger flexor muscles of 10 quadriplegic subjects were exercised via electrical stimulation to determine changes in the contractile force and fatigability of the muscle that could be externally induced. The force of contraction initially produced by most muscles was less than that required for functional activity. Following exercise, the strength of all muscles was increased above the level for functional use. In general, no correlation was noted between the amount of exercise and the force change. Two subjects had high contraction forces after prolonged periods before stimulation began, and 4 subjects who were followed after the stimulation program maintained near the contractile force achieved at the end of the program in the absence of stimulation. Fatigue of the muscle during the course of the exercise program was increased to above that recorded initially, although this was more variable and sometimes dropped to less than that recorded initially. Generally, no correlation was demonstrated between usage and fatigue. It is concluded that exercise induced by electrical stimulation alters the cantractile properties of the muscle toward a state usable for functional, tonic activation.