Low-frequency electrical stimulation with variable intensity preserves torque

The neuromuscular electrical stimulation (NMES) parameters that optimally modulate torque output during prolonged stimulation protocols are not well-established. The purpose of this study was to compare torque output between low-frequency and high-frequency NMES protocols while increasing stimulation intensity. Eleven healthy young individuals received a repetitive, intermittent low-frequency (20 Hz) and high-frequency (60 Hz) NMES over the quadriceps muscles. Stimulation intensity was increased throughout the protocol to achieve a submaximal target torque output. Mean torque, peak torque and torque-time integral (TTI) were measured. The 20 Hz protocol produced a higher mean torque (P = 0.001) and TTI (P = 0.008) compared to the 60 Hz protocol. The stimulation intensity required to achieve target torque during NMES was not different between frequencies (P > 0.0001). When the goal is to optimize torque output during prolonged submaximal NMES, such as during functional electrical stimulation, low-frequency stimulation may be preferred.