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Study Design A controlled laboratory study, with a single-blind, block-randomization crossover design. Objectives To compare the electrically elicited knee extensor torque produced by 3 clinically available waveforms: 2500-Hz burst-modulated alternating current (BMAC), 1000-Hz BMAC, and 1000-Hz burst-modulated biphasic square-wave pulsed current (BMBPC). Background Neuromuscular electrical stimulation (NMES) is the therapeutic use of electrical current to strengthen muscle. Muscle torque produced by NMES is limited by discomfort. Methods The knee extensor maximal volitional isometric torque (KEMVIT) of 33 able-bodied participants (18 female) was measured and used to normalize the electrically elicited knee extensor torque to produce a percent of KEMVIT (%KEMVIT). Electrically elicited isometric knee extensor torque was measured in response to each of the waveforms at the participants' maximum tolerance. Results The average maximum tolerated stimulation produced 32.0 ± 16.7 %KEMVIT with 2500-Hz BMAC, 38.2 ± 18.4 %KEMVIT with 1000-Hz BMAC, and 42.2 ± 17.1 %KEMVIT with 1000-Hz BMBPC. Tukey honest significant difference (HSD) post hoc testing revealed a statistically significant difference between 2500-Hz BMAC and 1000-Hz BMAC (P = .046), and between 2500-Hz BMAC and 1000-Hz BMBPC (P<.001). No statistically significant difference was found between 1000-Hz BMAC and 1000-Hz BMBPC (P = .267). Conclusion For eliciting maximum knee extensor muscle torque, 1000-Hz BMBPC and 1000-Hz BMAC were similarly effective, and 2500-Hz BMAC was less effective. J Orthop Sports Phys Ther 2018;48(3):217-224. Epub 19 Dec 2017. doi:10.2519/jospt.2018.7601.

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