Influence of Electrode Positioning and Current Type on Muscle Fatigability, Force Generation, Perceived Discomfort and Neuromuscular Adaptations Induced by Neuromuscular Electric Stimulation: Implications on Rehabilitation

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Introduction: Neuromuscular electrical stimulation (NMES) has the purpose of generating muscle contractions to minimize muscular atrophy and to improve neuromuscular performance. NMES has been performed using monophasic or biphasic currents, applied over a nerve trunk or muscle belly, and both can generate contractions by the peripheral and central nervous system. Pulse width (wide or narrow) is an essential parameter for NMES. Although NMES studies using wide pulses have been performed with monophasic currents, it is known that this current induces discomfort during NMES. Therefore, it is necessary to analyze if biphasic currents have the same effect as monophasic currents using the same parameters. Objectives: To compare the effects of NMES with narrow and wide pulse widths associated with monophasic and biphasic currents, applied over a tibial nerve and triceps surae muscles in healthy individuals in terms of muscle fatigue, central and peripheral contribution, voluntary and evoked force and sensory discomfort. Methods: A crossover, experimental controlled and randomized study will be developed with healthy male and female (age: 18-45 years). The following dependent variables will be: amplitude of H-reflex and M-wave (single and double pulses), voluntary and evoked triceps surae muscles torque, fatigability (force time integral), perceived discomfort and neuromuscular adaptations. The independent variables will be related to current phase, pulse width and location of electrical stimulation electrodes. There will be a familiarization session followed by 9 sessions with 7 rest days between them (10 weeks). Data will be reported as mean and standard deviation (± SD). Parametric tests will be used for the normally distributed data (Shapiro-Wilk test) that show homogeneous variations (Levene test). A repeated measure mixed-model ANOVA will be performed and, in the case of major effects or significant interactions, the Tukey post-hoc test will be applied. In addition, the power and size of the effect (reported as partial eta square, partial η2) will be calculated. The significance threshold will be set at p \<0.05 for all procedures. Expected results: Biphasic currents will be more comfortable and will generate less muscle fatigue when compared to monophasic currents. There will be less fatigue and greater central contribution when wider pulse currents will be applied over a nerve trunk concerning the application with a wide pulse over a muscle belly.

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