Optimal stimulus parameters for minimum pain in the chronic stimulation of innervated muscle.

The degree of pain reported by ten volunteers upon electrical stimulation of their peroneal nerves was measured while stimulus parameters were varied. The responses were compared for stimulations, all of which produced the same amount of ankle torque. The stimulation parameters examined were pulse duration, 0.3 and 1.0 msec; repetition frequence, 20, 50 and 100 hertz; pulse shape, square wave and exponential wave; impedance of stimulator output, constant voltage and constant current; direct current bias, positive or negative to the stimulus; and wave phase, uniphasic and biphasic. Pulse duration of 0.3 msec and constant voltage output were the only two parameters significantly associated with minimum pain response. Analysis of voltage and current wave forms for the different stimulus parameters indicated that the sensation of pain was dependent upon the total amount of electrical charge delivered to the tissue with the pulse.