BACKGROUND: Neuromuscular electrical stimulation (NMES) is a widely used technique for rehabilitation in physical therapy, however it causes muscle fatigue more rapidly than does voluntary contraction. In clinical practice, it becomes necessary to monitor muscle fatigue during NMES protocols to adjust the parameters of electrical current stimulation and, thus, increase stimulation time. OBJECTIVES: The aim of this study is to use mechanomyography (MMG) as a means of evaluating peripheral muscle fatigue during the execution of an NMES protocol. METHODS: An MMG signal acquisition system and an experimental protocol were developed. During in vivo tests, 10 participants performed maximal voluntary contractions (MVCs) for knee extension. A maximization phase was conducted with dynamic contractions generated by NMES at 10% of MVC (100 Hz, 400 µs) on the quadriceps muscle, and the main NMES protocol occurred at 30% of MVC (50 Hz, 400 µs). Simultaneously, MMG RMS (amplitude) and MMG MPF (frequency) signals of the rectus femoris and the knee extension torque were acquired. RESULTS: The tendency line of the MMG RMS was descendant, indicating that MMG RMS correlates with torque amplitude. However, MMG MPF did not show a significant correlation with torque for the present NMES protocol. CONCLUSIONS: MMG is a technique that can be simultaneously applied to NMES because there is no electrical interference and it can be used during functional movements in the NMES-generated muscle contraction. Article registered in the Australian New Zealand Clinical Trials Registry (ANZCTR) under the number ACTRN12609000866202.
neuromuscular electrical stimulation; muscle fatigue; mechanomyography; rectus femoris muscle
