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Motor unit recruitment during neuromuscular electrical stimulation: a critical appraisal

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Abstract

Neuromuscular electrical stimulation (NMES) is commonly used in clinical settings to activate skeletal muscle in an effort to mimic voluntary contractions and enhance the rehabilitation of human skeletal muscles. It is also used as a tool in research to assess muscle performance and/or neuromuscular activation levels. However, there are fundamental differences between voluntary- and artificial-activation of motor units that need to be appreciated before NMES protocol design can be most effective. The unique effects of NMES have been attributed to several mechanisms, most notably, a reversal of the voluntary recruitment pattern that is known to occur during voluntary muscle contractions. This review outlines the assertion that electrical stimulation recruits motor units in a nonselective, spatially fixed, and temporally synchronous pattern. Additionally, it synthesizes the evidence that supports the contention that this recruitment pattern contributes to increased muscle fatigue when compared with voluntary actions and provides some commentary on the parameters of electrical stimulation as well as emerging technologies being developed to facilitate NMES implementation. A greater understanding of how electrical stimulation recruits motor units, as well as the benefits and limitations of its use, is highly relevant when using this tool for testing and training in rehabilitation, exercise, and/or research.

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Authors and Affiliations

  1. Department of Physical Therapy, University of Alabama at Birmingham, SHPB 387; 1530 3rd Avenue South, Birmingham, AL, 35294-1212, USA

    C. Scott Bickel

  2. Department of Health Sciences and Research, Medical University of South Carolina, Charleston, SC, USA

    Chris M. Gregory

  3. Department of Health Professions, Division of Physical Therapy, Medical University of South Carolina, Charleston, SC, USA

    Jesse C. Dean

Authors
  1. C. Scott Bickel
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  2. Chris M. Gregory
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  3. Jesse C. Dean
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Correspondence to C. Scott Bickel.

Additional information

Communicated by Roberto Bottinelli.

This article is published as part of the Special Issue Cluster on the XVIII Congress of the International Society of Electrophysiology and Kinesiology (ISEK 2010) that took place in Aalborg, Denmark on 16–19 June 2010.

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Bickel, C.S., Gregory, C.M. & Dean, J.C. Motor unit recruitment during neuromuscular electrical stimulation: a critical appraisal. Eur J Appl Physiol 111, 2399–2407 (2011). https://doi.org/10.1007/s00421-011-2128-4

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