High voltage versus low voltage electrical stimulation. Force of induced muscle contraction and perceived discomfort in healthy subjects.

High voltage pulsed galvanic stimulation (HVPGS) and low voltage neuromuscular stimulation (LVNMS) techniques were compared for peak torque of an induced isometric contraction, perceived discomfort, and subjective preference of treatment. The high voltage current used a 40-microseconds monophasic waveform, and the low voltage current used a 300-microseconds biphasic waveform. Both currents used a pulse rate of 50 pps. Both HVPGS and LVNMS were administered to one muscle group, either knee extensors or plantar flexors, of 24 healthy subjects. An isokinetic dynamometer was used to assess peak torque. The perceived discomfort experienced with each type of electrical stimulation was quantified by the use of a visual analog scale. For all dependent measures, data first were analyzed for the whole treatment group and then analyzed for each subgroup. Correlated t tests for the whole group and the plantar flexor muscle subgroup demonstrated that HVPGS produced a significantly greater average peak force of muscle contraction than LVNMS and HVPGS was perceived to be significantly less uncomfortable than LVNMS. No significant differences were found between treatments in the knee extensor muscle subgroup for these dependent variables. Chi-square analysis revealed a subject preference for HVPGS in the whole group and in both subgroups. This study indicates that HVPGS can produce a stronger, less uncomfortable, induced isometric muscle contraction than LVNMS.