Effects of Neuromuscular Electrical Stimulation Parameters on Torque, Fatigue, and Oxygen Extraction

Neuromuscular Electrical Stimulation (NMES) can minimize muscle atrophy, complications related to muscle disuse and improved neuromuscular performance. However, it is still unclear the influence of specific physical parameters, including carrier frequency, burst duration, and duty cycle regarding the greater generation of evoked torque, sensory discomfort, muscle fatigue, and peripheral oxygen extraction. Thus, the aim of this study is to compare the effects of different NMES protocols applied to the triceps surae muscle for evoked torque, muscle fatigue, sensory discomfort, and peripheral oxygen extraction in healthy individuals. This is a crossover, experimental, randomized, double-blind trial composed of apparently healthy participants. All NMES protocols will be tested on the same individual with randomization of the sequence of intervention protocols. There will be a total of 6 encounters with seven days between them. Session 1 will evaluate the anthropometric measures, the maximum intensity for each intervention protocol, and the sequence of intervention protocols for each individual will be randomized. Sessions 2, 3, 4, and 5 will be composed equally with the assessment of the maximum voluntary and evoked joint torque of the triceps surae muscle through the isokinetic dynamometer, evaluation of muscle fatigue through the H-reflex, M-wave, fatigue index, time-torque-integral, and recruitment curve, evaluation of peripheral oxygen extraction through NIRS (Near Infrared Spectroscopy), electromyographic signals to assessed the RMS (root mean square) and the median frequency, evaluation of the level of sensory discomfort through the Visual Analog Pain Scale and finally by the NMES protocol. The 6th session will be the replication of the 2nd session of each individual. The EENM protocols will be as follows: CR10% (Russian Current with 2500 Hz, modulated in bursts of 50 Hz, 200 µs and 10% duty cycle - 2 ms bursts and 18 ms interbusrts), CR20% (Russian Current with 2