Transcutaneous electrical nerve stimulation(TENS) for human beings has been used increasingly as the therapeutic tools, but there has been little clear explanation for site, intensity, freguency and duration of stimulation, mechanism of action and therapeutic effectiveness.

The purpose of this study was to investigate the mechanism of action of TENS by recording the H-reflex after TENS application.

The 33 healthy adult volunteers were stimulated by TENS for 5 min or 15 min or 30 min. The onset latency, amplitude, and H/M ratio of H-reflex were measured before, and immediately, at 15 min and 30 min after stimulation of TENS.

Onset latency of H-reflex was significantly delayed immediately after application of TENS but recovered at 15 min and 30 min after stimulation of TENS, irrespective of duration of stimulation of TENS. Amplitude of H-reflex was not significantly changed. H/M ratio of H-reflex showed variable change.

As the above results, we could not find the long lasting effect of conventional TENS on the H-reflex that favored endorphin theory. We concluded that the polysynaptic inhibition of spinal motoneuron excitability was favored as the mechanism of conventional TENS.