Effects of involuntary eccentric contraction training by neuromuscular electrical stimulation on the enhancement of muscle strength

Background: Neuromuscular electrical stimulation is well-known as a modality to improve the performance of neuromuscular system, but its clinical value on muscle strengthening remains equivocal. In this study, we designed a system for an involuntary eccentric contraction of biceps brachii muscles using continuous passive movement and commercial neuromuscular electrical stimulation devices. Methods: To investigate the effects of involuntary eccentric contraction training by neuromuscular electrical stimulation on the enhancement of muscle strength, seven healthy men between the ages of 24 and 29 years participated in this study. Participants were trained two times per week for 12 weeks. Each exercise session was performed for 30minwith no rest intervals. Isometric elbowflexion torque and biceps brachiimuscle thickness were chosen as evaluation indices, and were measured at pre-/post-training. Findings: After the 12-week training, the isometric elbowflexion torque of the trained side significantly increased by approximately 23% compared to the initial performance (P < 0.01). Meanwhile, the torque of the untrained side showed no significant change (P = 0.862). During the 12-week training period, the biceps brachii muscle thickness of the trained side significantly increased by around 8% at rest and 16% at maximum voluntary contraction (P < 0.01). Interpretation: The developed system and the technique show promising results, suggesting that it has the potential to be used to increase the muscle strength in patients with neuromuscular disease and to be implemented in design rehabilitative protocols.