Motor unit recruitment during neuromuscular electrical stimulation: a critical appraisal

• Published in: European journal of applied physiology Vol. 111; no. 10; pp. 2399 - 2407
• Main Authors: Bickel, C. Scott, Gregory, Chris M., Dean, Jesse C.
• Format: Journal Article Conference Proceeding
• Language: English
• Published: Berlin/Heidelberg Springer-Verlag 01-10-2011; Springer; Springer Nature B.V
• Subjects: Animals; Biological and medical sciences; Biomedical and Life Sciences; Biomedicine; Content analysis; Electric Stimulation - methods; Electric Stimulation Therapy - methods; Electrical stimuli; Electromyography; Fatigue; Fundamental and applied biological sciences. Psychology; Human Physiology; Humans; Mini Review; Motor units; Muscle contraction; Muscle Contraction - physiology; Muscle Fatigue - physiology; Musculoskeletal system; Neuromuscular electrical stimulation; Neuromuscular Junction - physiology; Occupational Medicine/Industrial Medicine; Physical therapy; Physical training; Recruitment; Recruitment, Neurophysiological - physiology; Rehabilitation; Skeletal muscle; Sports Medicine; Vertebrates: body movement. Posture. Locomotion. Flight. Swimming. Physical exercise. Rest. Sports; United States > US; Electrical stimulation; Motor unit recruitment; Skeletal muscle; Human; Electrical stimulus; Striated muscle; Motor unit; Recruitment
• ISSN: 1439-6319; 1439-6327
• DOI: 10.1007/s00421-011-2128-4

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.