Effects of Neuromuscular Electrical Stimulation on the Muscle Hypertrophy and Cross Training Effect

ABSTRACT

OBJECTIVE: To evaluate the effect of electrical stimulation on muscle strength, muscle bulk and envelope amplitude. METHOD: Twenty right handed healthy men and women (8 12) volunteered to be subjects whose mean age were 25.5+/-2.8 years. Left thenar muscle was stimulated at 40 Hz frequency for 20 minutes, every weekday for 2 weeks. Maximal tip pinch power of first and second finger, and cross sectional area of abductor pollicis brevis were assessed before and after electrical stimulation in both hands. RESULTS: Maximal tip pinch power increased in bilateral hands. The thickness and cross sectional area of both thenar muscles were increased, but they were significant only in left side. Envelope amplitude increased significantly in left thenar muscle at maximal voluntary contraction, and showed a tendency to increase in right side at each percent of 10, 30, 50, 100 and in left side at 10, 30, 50% maximal voluntary contractions. CONCLUSION: The electrical stimulation on unilateral muscle induced the increment of bilateral muscular strength. The neural factor and muscle hypertrophy are responsible for the increased strength of the stimulated muscle and the increase in the nonstimulated muscle strength is related to the cross-training effect and adaptation effect.