The effects of wide pulse neuromuscular electrical stimulation on elbow flexion torque in individuals with chronic hemiparetic stroke

Objective: Neuromuscular electrical stimulation that incorporates wide pulse widths (1 ms) and high frequencies (100 Hz; wide pulse-NMES (WP-NMES)) augments contractions through an increased reflexive recruitment of motoneurons in individuals without neurological impairments and those with spinal cord injury. The current study was designed to investigate whether WP-NMES also augments contractions after stroke. We hypothesized that WP-NMES would generate larger contractions in the paretic arm compared to the non-paretic arm due to increased reflex excitability for paretic muscles after stroke. Methods: The biceps brachii muscles were stimulated bilaterally in 10 individuals with chronic hemiparetic stroke. Four stimulation patterns were delivered to explore the effects of pulse width and frequency on contraction amplitude: 20-100-20 Hz (4 s each phase, 1 ms pulse width); 20-100-20 Hz (4 s each phase, 0.1 ms); 20 Hz for 12 s (1 ms); and 100 Hz for 12 s (1 ms). Elbow flexion torque and electromyography were recorded. Results: Stimulation that incorporated 1 ms pulses evoked more torque in the paretic arm than the non- paretic arm. When 0.1 ms pulses were used there was no difference in torque between arms. For both arms, torque declined significantly during the constant frequency 100 Hz stimulation and did not change during the constant frequency 20 Hz stimulation. Conclusions: The larger contractions generated by WP-NMES are likely due to increased reflexive recruitment of motoneurons, resulting from increased reflex excitability on the paretic side. Significance: NMES that elicits larger contractions may allow for development of more effective stroke rehabilitation paradigms and functional neural prostheses. (C) 2012 International Federation of Clinical Neurophysiology. Published by Elsevier Ireland Ltd. All rights reserved.