Electrically Elicited Quadriceps Muscle Torque: A Comparison of 3 Waveforms

Area of Science:

• Rehabilitation Medicine
• Biomedical Engineering
• Sports Science

Background:

• Neuromuscular electrical stimulation (NMES) enhances muscle strength but can be limited by patient discomfort.
• Optimizing NMES waveforms is crucial for maximizing therapeutic benefits and patient tolerance.
• Understanding waveform-specific torque production is essential for effective clinical application.

Purpose of the Study:

• To compare the knee extensor torque elicited by three distinct NMES waveforms.
• To evaluate the effectiveness of 2500-Hz burst-modulated alternating current (BMAC), 1000-Hz BMAC, and 1000-Hz burst-modulated biphasic square-wave pulsed current (BMBPC).
• To determine which waveform produces the greatest torque at maximum tolerable stimulation intensity.

Main Methods:

• A controlled laboratory study utilizing a single-blind, block-randomization crossover design.
• Thirty-three healthy participants (18 female) underwent isometric knee extensor torque testing.
• Torque was normalized to maximal volitional isometric torque (%KEMVIT) and measured at maximum tolerated stimulation for each waveform.

Main Results:

• The 1000-Hz BMBPC waveform produced the highest average tolerated torque (%KEMVIT: 42.2 ± 17.1).
• The 1000-Hz BMAC waveform yielded 38.2 ± 18.4 %KEMVIT, while 2500-Hz BMAC produced 32.0 ± 16.7 %KEMVIT.
• Statistically significant differences were found between 2500-Hz BMAC and both 1000-Hz waveforms (P<.001 and P=.046, respectively).

Conclusions:

• For eliciting maximal knee extensor muscle torque, 1000-Hz BMBPC and 1000-Hz BMAC are similarly effective.
• The 2500-Hz BMAC waveform is less effective for generating knee extensor torque compared to the 1000-Hz waveforms.
• These findings suggest waveform selection impacts NMES efficacy in torque production.