Electrical stimulation factors in potentiation of human quadriceps femoris.

Potentiation is the enhancement of force seen after repetitive activation of skeletal muscle. The frequency and duration of stimulation, total number of pulses delivered to the muscle, and the peak forces or force-time integrals produced by the stimulation all have been suggested to affect the degree of potentiation. The purpose of this study was to determine the effect of the electrical stimulation characteristics on the development of post-activation potentiation. Eleven subjects were tested with five potentiating trains, including 12-pulse 100-HZ, 31-HZ, 14-HZ, and 5-HZ, and 6-pulse 14-HZ trains. The potentiating trains differed in stimulation frequency, train duration, and total number of pulses. They also produced different peak forces and force time integrals from the activated muscles. Our results showed that the 12-pulse 5-HZ train produced about 50% less potentiation than the other four potentiating trains. At stimulation frequencies of 14 HZ or higher, the total number of pulses delivered to the muscle was the primary factor in potentiation development. Furthermore, peak force and force-time integral had no effects on the rate or amount of potentiation. These results should help clinicians and researchers to design protocols that control for the effects of muscle potentiation.