Effects of Narrow- versus Wide-Pulse Neuromuscular Electrical Stimulation Training on Isometric Strength and Underlying Neuromuscular Adaptations

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PURPOSE: The training effects of neuromuscular electrical stimulation (NMES) delivered with narrow pulses are relatively well known. Wide-pulse NMES has recently received increasing attention, but mainly for acute applications. The aim of the present study was to investigate the effect of NMES training with narrow versus wide pulses on isometric strength and on the underlying neuromuscular adaptations. METHODS: Thirty-six healthy men were randomly allocated to a control group and two NMES training groups (narrow-pulse group (NG) and wide-pulse group (WG)). Trained participants completed a 6-wk NMES program, followed by a 6-wk detraining period. NMES with narrow (0.2 ms) or wide (1 ms) pulses was applied to the quadriceps at a stimulation frequency of 50 Hz and at maximal tolerable current intensity. All participants completed three testing sessions: before (PRE) and after (POST) training, as well as after the detraining period (DE). Measurements included ultrasonography, maximal voluntary contractions (MVC) with the twitch interpolation technique, and transcranial magnetic and peripheral nerve stimulations. RESULTS: MVC torque increased significantly and similarly for the two NMES training groups, from PRE-to-POST (11% and 12% for NG and WG, respectively) and PRE-to-DE (12% and 7% for NG and WG, respectively). This was associated with significant and similar increases of voluntary activation, evoked doublet torque, and muscle thickness in both groups. A significant cross-education effect was also observed for both groups (8% and 10% for NG and WG, respectively). No changes in corticospinal responsiveness were observed. CONCLUSIONS: Despite differences in total applied current, narrow- and wide-pulse NMES training induced similar isometric strength gains, and neural and muscular adaptations in healthy men, likely due to a comparable level of evoked torque throughout the training programs.

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