Part I: Effects of Asynchronous vs Conventional Synchronous Neuromuscular Electrical Stimulation on Maximal Evoked Torque, Fatigability, Discomfort, and Strength Gains - A Systematic Review with Meta-Analysis and Meta-Regression.
systematic_review · Level I
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- Record sourced from PubMed, PMID 41285274.
- Also identified by DOI 10.1016/j.apmr.2025.10.026.
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Abstract
To compare the effects of asynchronous versus conventional synchronous neuromuscular electrical stimulation (NMES) on evoked torque, fatigability, discomfort, and training-induced strength gains. A systematic search was conducted in six electronic databases (PubMed, EMBASE, PEDro, LILACS, SciELO, and Web of Science) for studies published up to April 2025. Guided by a PICOT framework, we combined terms for the population (humans), intervention (electrical stimulation), comparator (synchronous, asynchronous, spatially distributed sequential, conventional), and outcomes (torque, muscle strength, fatigue, discomfort, evoked contraction). We included cross-sectional, repeated-measures or randomized controlled trials of adult or elderly participants (healthy or clinical) receiving electrically induced isometric or dynamic contractions without voluntary effort. Comparisons involved synchronous vs. asynchronous current delivery. Outcomes were maximal evoked torque, fatigability, perceived discomfort, and strength adaptations. A total of 22 studies were included from 11,043 records. Two independent reviewers extracted participant demographics, stimulation parameters, electrode configurations, and outcomes. Study quality was assessed with the PEDro scale and evidence quality via GRADE. Meta-analysis showed asynchronous NMES produced greater isometric evoked torque than synchronous NMES (p<0.01; SMD 95% CI: 0.245, 0.957), especially when using larger electrodes (p=0.042, β=0.0023). No difference was found in dynamic evoked torque (p=0.95; 95% CI: -1.44, 1.35). Fatigability was significantly lower with asynchronous NMES for both isometric (p<0.01; SMD 95% CI: 0.49, 1.21) and dynamic contractions (p<0.01; SMD 95% CI: 0.61, 2.76). Discomfort and strength data were insufficient for firm conclusions. Asynchronous NMES effectively reduces muscle fatigability compared to synchronous stimulation. These findings may help clinicians and researchers in optimizing NMES protocols and support the development of asynchronous NMES solutions for clinical use.