Effects of different electrical stimulation currents and phase durations on submaximal and maximum torque, efficiency, and discomfort: a randomized crossover trial

•KFAC and PC NMES induced similar relative submaximal and maximum evoked-torque and perceived discomfort for a given phase duration.•Regardless of NMES-type, the wider phase duration resulted in higher current NMES-efficiency in generating evoked-torque.•For different types of current, intensity was not related to the maximum perceived discomfort to produce submaximal contractions. Neuromuscular electrical stimulation (NMES) is an important therapeutic tool for rehabilitation. However, best stimulation parameters remain to be determined. To determine the influence of different electrical stimulation currents and phase durations on torque, efficiency, and discomfort. Using a cross-over design, kHz frequency alternating currents (KFAC) and pulsed currents (PC) with narrow (200 µs) or wide (500 µs) phase durations were randomly applied on knee extensor muscles of healthy participants with a minimum of seven days between sessions. The NMES-evoked torque, NMES-efficiency, and discomfort (visual 0−10 cm analogue scale) were measured for each stimulation intensity increments (10 mA). Statistics were conducted using a three-way analysis of variances (phase duration x current x intensity), followed by Tukey post-hoc. Twenty-four males (age 22.3 ± 3.5years) were included. No effect of NMES current was observed for torque, efficiency, and discomfort. For wide phase durations (500 µs), torque significantly increased for all stimulation intensities. For narrow phase durations (200 µs) evoked torque significantly increased only after 40% of maximal stimulation intensity. Phase durations of 500 µs produced greater torque than 200 µs. Discomfort was greater with 500 µs when compared to 200 µs. Submaximal relative torque, for example 40% of maximum voluntary contraction (MVC), was obtained with ∼ 60% and ∼ 80% of the maximal current intensity for 500 µs and 200 µs, respectively. KFAC and PC current applied with the same phase duration induced similar relative submaximal and maximum evoked-torque, efficiency, and perceived discomfort. However, currents with 500 µs induced higher evoked-torque, current efficiency, and perceived discomfort.