Utilising physiological principles of motor unit recruitment to reduce fatigability of electrically-evoked contractions: A narrative review

Publication date: Available online 19 September 2017
Source:Archives of Physical Medicine and Rehabilitation
Author(s): Trevor S. Barss, Emily N. Ainsley, Francisca C. Claveria-Gonzalez, M John Luu, Dylan J. Miller, Matheus J. Wiest, David F. Collins
Neuromuscular electrical stimulation (NMES) is used to produce contractions to restore movement and reduce secondary complications for individuals experiencing motor impairment. NMES is conventionally delivered through a single pair of electrodes over a muscle belly or nerve trunk using short pulse durations and frequencies between 20–40 Hz (conventional NMES). Unfortunately, the benefits and widespread use of conventional NMES are limited by contraction fatigability, which is due in large part to the non-physiological way that contractions are generated. This review provides a summary of approaches designed to reduce fatigability during NMES, by utilising physiological principles that help minimise fatigability of voluntary contractions. First, relevant principles of the recruitment and discharge of motor units (MUs) inherent to voluntary contractions and conventional NMES are introduced and the main mechanisms of fatigability for each contraction type are briefly discussed. A variety of NMES approaches are then described which were designed to reduce fatigability by generating contractions that more closely mimic voluntary contractions. These approaches include altering stimulation parameters, to recruit MUs in their physiological order, and stimulating through multiple electrodes, to reduce MU discharge rates. Although each approach has unique advantages and disadvantages, approaches that minimise MU discharge rates hold the most promise for imminent translation into rehabilitation practice. The way that NMES is currently delivered limits its utility as a rehabilitative tool. Reducing fatigability by delivering NMES in ways that better mimic voluntary contractions holds promise for optimizing the benefits and widespread use of NMES-based programs.



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