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

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.

Cross Training Effect Following Unilateral Leg Strengthening Exercise

OBJECTIVE: To examine the effects of unilateral leg exercise on the contralateral leg and the cross training effect according to the training intensity. METHOD: Nineteen healthy males volunteered to be subjects for this investigation and were divided into a training group (N=13) and a control group (N=6). One leg of each subject in the training group was randomly assigned to a six week, three day/week isokinetic strengthening training program for concentric knee extension-flexion performed at 60 degrees/second (group A, N=6) and 180 degrees/second (group B, N=7). The control group did not train for six weeks. The strength of the knee extensor and flexor was tested before and after the six week period training by Cybex 770 dynamometer. RESULTS: In both groups A and B, the training resulted in significant increase of knee extensor strength in trained limb compared to control group. However, the strength increment of untrained limb was not significant compared to control group. CONCLUSION: There was no significant cross training effect following unilateral leg strength exercise.