Wide pulse-width, high-frequency electrical stimulation: Implications for neuromuscular electrical stimulation

Electrical stimulation using 1 ms pulse-widths, delivered at 100 Hz, produces torques larger than expected from direct motor axon activation alone. These stimulation parameters were delivered over the tibial nerve, median nerve, plantar and wrist flexors to induce contractions through direct motor axon activation and excitation of motoneurons through sensory axons (extra contractions). Absolute and extra contraction amplitudes, along with consistency between contractions and stability within single contractions were compared between nerve and muscle stimulation at low and moderate intensities. Extra contractions were produced in plantar and wrist flexors with nerve and muscle stimulation at each intensity. Moderate intensity muscle stimulation of the triceps surae produced the largest absolute torques and low intensity muscle stimulation evoked the largest extra contractions. Low intensity tibial nerve stimulation produced the least consistent and stable contractions. Absolute and extra contraction amplitudes were similar for all conditions in the wrist flexors.