FATIGUE REDUCTION BY SEQUENTIAL STIMULATION OF MULTIPLE MOTOR POINTS IN A MUSCLE

The purpose of this study was to determine the optimal method of stimu lating multiple motor points in a muscle in an attempt to improve fati gue resistance. The long head of triceps, which has 2 to 3 motor point s, 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 define d based on the stimulation pattern of the muscle: (1) Group A1: The pr oximal motor point was stimulated at 20 Hz; (2) Group A2: The distal m otor point was stimulated at 20 Hz; (3) Group B: Both motor points wer e stimulated simultaneously at 20 Hz; (4) Group C: Both proximal and d istal motor points were stimulated at alternate intervals of 10 second s at 20 Hz; and (5) Group D: Both motor points were stimulated sequent ially at 10 Hz. Each test was conducted for 6 minutes. In sequential s timulation (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 elec trical stimulation, electrodes should be inserted into all motor point s for a given muscle. Sequential stimulation of these points can impro ve fatigue resistance.