Mechanomyography for the Measurement of Muscle Fatigue Caused by Repeated Functional Electrical Stimulation

An attempt at utilizing mechanomyography (MMG) to quantify muscle fatigue, which occurs on account of repeated functional electrical stimulations (FES), is presented. Twenty-one subjects participated in the experiment, wherein a constant electrical stimulation was repeatedly applied to the tibialis anterior muscle. MMG signals were measured simultaneously, as the stimulations were applied, and subsequently quantified using 8 different methods. Muscle fatigue was confirmed by observing linearly decreasing ankle-joint torque with the repetition of the electrical stimulation (r² = 0.7823). The convex-hull area and volume along with peak-to-peak MMG signals were found to demonstrate significant linear relationships with muscle fatigue in spite of the weakness in motion artifacts. Use of the Lempel-Ziv algorithm, based on three symbols, provided the most accurate correlations for muscle fatigue. However, frequency-based characteristics as well as mean and median frequencies did not demonstrate any significant linearity with muscle fatigue.