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Utilizing Physiological Principles of Motor Unit Recruitment to Reduce Fatigability of Electrically-Evoked Contractions: A Narrative Review

  • Trevor S. Barss
    Affiliations
    Human Neurophysiology Laboratory, Faculty of Physical Education and Recreation, University of Alberta, Edmonton, AB, Canada
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  • Emily N. Ainsley
    Affiliations
    Human Neurophysiology Laboratory, Faculty of Physical Education and Recreation, University of Alberta, Edmonton, AB, Canada

    Neuroscience and Mental Health Institute, University of Alberta, Edmonton, AB, Canada
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  • Francisca C. Claveria-Gonzalez
    Affiliations
    Human Neurophysiology Laboratory, Faculty of Physical Education and Recreation, University of Alberta, Edmonton, AB, Canada

    Faculty of Rehabilitation Medicine, University of Alberta, Edmonton, AB, Canada
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  • M. John Luu
    Affiliations
    Human Neurophysiology Laboratory, Faculty of Physical Education and Recreation, University of Alberta, Edmonton, AB, Canada

    Neuroscience and Mental Health Institute, University of Alberta, Edmonton, AB, Canada
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  • Dylan J. Miller
    Affiliations
    Human Neurophysiology Laboratory, Faculty of Physical Education and Recreation, University of Alberta, Edmonton, AB, Canada
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  • Matheus J. Wiest
    Affiliations
    Human Neurophysiology Laboratory, Faculty of Physical Education and Recreation, University of Alberta, Edmonton, AB, Canada

    Biomechanics Laboratory, Department of Physical Education, Federal University of Santa Catarina, Florianópolis, Brazil
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  • David F. Collins
    Correspondence
    Corresponding author David F. Collins, PhD, 4-219 Van Vliet Complex, University of Alberta, Edmonton, AB T6G 2H9, Canada.
    Affiliations
    Human Neurophysiology Laboratory, Faculty of Physical Education and Recreation, University of Alberta, Edmonton, AB, Canada

    Neuroscience and Mental Health Institute, University of Alberta, Edmonton, AB, Canada
    Search for articles by this author
Published:September 18, 2017DOI:https://doi.org/10.1016/j.apmr.2017.08.478

      Abstract

      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 and 40Hz (conventional NMES). Unfortunately, the benefits and widespread use of conventional NMES are limited by contraction fatigability, which is in large part because of the nonphysiological way that contractions are generated. This review provides a summary of approaches designed to reduce fatigability during NMES, by using physiological principles that help minimize 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 that 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 minimize 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.

      Keywords

      List of abbreviations:

      H-reflex (Hoffman reflex), M-wave (motor wave), MU (motor unit), NMES (neuromuscular electrical stimulation), SCI (spinal cord injury)
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