Effects of nerve stimulation on human muscle.

A phasic program of femoral nerve stimulation was used to reduce refractory knee flexion contractures in five patients. In one, rectus femoris was tenotomized before starting stimulation to reduce hip flexion contracture. Muscle biopsies were performed before and after 5 to 12 weeks of intermittent stimulation at separated sites on the same muscle. In the four patients where muscle contraction was isometric, type I fibers increased 3.7%, 6.4%, 48.4%, anand 30.4%, respectively. Both fiber types in each patient showed an increase in size ( p less than .001). In the tenotomized muscle, where contraction was isotonic at a shortened length, the proportion of type I fibers decreased from 40.2% to 25.4%, and their mean diameter also decreased (p less than .001). These observations suggest that the physical conditions of contraction may be more important than the pattern of neuronal discharge in determining the metabolic profile of human muscle fibers.