Comparison of peak torque, intensity and discomfort generated by neuromuscular electrical stimulation of low and medium frequency

Abstract

BACKGROUND AND PURPOSE: Neuromuscular electrical stimulation (NMES) is an important tool in clinical practice to improve the recruitment of motor units. Optimal forms of NMES, as well as the optimal frequency to achieve the highest torque with the least possible discomfort are not well established. This study was designed to compare maximum electrically-induced torque (MEIT) in the quadriceps, the maximum intensity tolerated by the subject, and the level of discomfort generated by three types of stimulation. METHODS: Thirty subjects (mean age of 25.0 ± 3.0 years) participated in the study. Each subject was submitted to three currents: medium frequency (2500 Hz) modulated in low frequency (Russian Current), and two currents of low frequency (50 Hz), i.e. without an intrapulse interval (FES), and another with an intrapulse interval of 100 µs (VMS). The maximum voluntary isometric torque (MVIT) of the quadriceps was measured. The MEIT, the level of discomfort, and the maximum intensity reached were also measured while applying the three types of NMES. The order of the tests was randomized and the torque was normalized in relation to MVIT. RESULTS: The results showed no significant difference between the three types of NMES in relation to the generated torque. However, the subjects were able to tolerate a significantly higher intensity with the medium frequency current, and suffered less discomfort when compared to subjects exposed to low frequency currents. CONCLUSION: Russian Current, FES, and VMS can be used clinically in order to increase the torque of the quadriceps muscle. However, we suggest using the Russian Current in the early stages of a rehabilitation protocol because it showed better tolerance by the participants with less discomfort.