Interleaved neuromuscular electrical stimulation: Motor unit recruitment overlap.

Introduction: In this study, we quantified the "overlap" between motor units recruited by single pulses of neuromuscular electrical stimulation (NMES) delivered over the tibialis anterior muscle ( mNMES) and the common peroneal nerve (nNMES). We then quantified the torque produced when pulses were alternated between the mNMES and nNMES sites at 40 HZ ("interleaved" NMES; iNMES). Methods: Overlap was assessed by comparing torque produced by twitches evoked by mNMES, nNMES, and both delivered together, over a range of stimulus intensities. Trains of iNMES were delivered at the intensity that produced the lowest overlap. Results: Overlap was lowest ( 5%) when twitches evoked by both mNMES and nNMES produced 10% peak twitch torque. iNMES delivered at this intensity generated 25% of maximal voluntary dorsiflexion torque (11 Nm). Discussion: Low intensity iNMES leads to low overlap and produces torque that is functionally relevant to evoke dorsiflexion during walking.