Stimulus-response latencies of two instruments delivering transcutaneous electrical neuromuscular stimulation (TENS).

Stimulus-response latencies of low-frequency transcutaneous electrical neuromuscular stimulation (TENS) were studied in 15 healthy subjects, applying the two different pulse configurations delivered by the Biotens and the Myomonitor instruments. Latencies, in milliseconds, were determined on bipolar raw surface electromyograms (EMG) of the suprahyoid muscles, using the skin surface over the sigmoid notches of the mandible as the site of stimulation. Stimulus-response times were measured from the onset of the stimulus artefact to the first response peak on EMG, and their mean values showed ranges of 3.79-4.49 ms for Biotens and 5.10-5.34 ms for Myomonitor. It was concluded that low-frequency TENS caused direct stimulation of motor nerves, and that the timing of the contraction response was not affected by altered electrode placement, lead-wire reversal or unbalanced (right/left) stimulation.