Recruitment Patterns in Human Skeletal Muscle During Electrical Stimulation

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Abstract
Electromyostimulation (EMS) incorporates the use of electrical current to activate skeletal muscle and facilitate contraction. It is commonly used in clinical settings to mimic voluntary contractions and enhance the rehabilitation of human skeletal muscles. Although the beneficial effects of EMS are widely accepted, discrepancies concerning the specific responses to EMS versus voluntary actions exist. The unique effects of EMS have been attributed to several mechanisms, most notably a reversal of the recruitment pattern typically associated with voluntary muscle activation. This perspective outlines the authors' contention that electrical stimulation recruits motor units in a nonselective, spatially fixed, and temporally synchronous pattern. Furthermore, it synthesizes the evidence that supports the contention that this recruitment pattern contributes to increased muscle fatigue when compared with voluntary actions. The authors believe the majority of evidence suggests that EMS-induced motor unit recruitment is nonselective and that muscle fibers are recruited without obvious sequencing related to fiber types.