In this study, a training system for an involuntary eccentric contraction of biceps brachii muscles was designed using a continuous passive movement and a commercial neuromuscular electrical stimulation devices. To investigate the effects of the involuntary eccentric contraction training by neuromuscular electrical stimulation on the enhancement of muscle strength, 7 healthy males participated, who were trained two times per week for 12 weeks. Each exercise session was performed for 30 minutes with no rest intervals. Isometric elbow flexion torque and biceps brachii muscle thickness were chosen as evaluation indices, and were measured at pre-/posttraining. After the 12-week training, the isometric elbow flexion torques significantly increased by approximately 23% compared to the initial performance (p < 0.01). In addition, the biceps brachii muscle thicknesses significantly increased by around 8% at rest and 16% at MVC (p < 0.01). 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.