Fatigue reduction by sequential stimulation of multiple motor points in a muscle

The purpose of this study was to determine the optimal method of stimulating multiple motor points in a muscle in an attempt to improve fatigue resistance. The long head of triceps, which has 2 to 3 motor points, in an adult New Zealand white rabbit was used as the muscle model. The fatigue index, defined as the percentage of maximum force at time t, was compared during the fatigue tests. Five test groups were defined based on the stimulation pattern of the muscle: (1) Group A1: The proximal motor point was stimulated at 20 Hz; (2) Group A2: The distal motor point was stimulated at 20 Hz; (3) Group B: Both motor points were stimulated simultaneously at 20 Hz; (4) Group C: Both proximal and distal motor points were stimulated at alternate intervals of 10 seconds at 20 Hz; and (5) Group D: Both motor points were stimulated sequentially at 10 Hz. Each test was conducted for 6 minutes. In sequential stimulation (Group D), the fatigue index was significantly higher when compared with the other test groups at Minutes 4, 5, and 6. In groups A1, A2, B, and C, there were no significant differences in the fatigue indices. For optimal control of muscle contraction in functional electrical stimulation, electrodes should be inserted into all motor points for a given muscle. Sequential stimulation of these points can improve fatigue resistance.