Consistency of the optimized bandwidth in filter-based fatigue index

In this study, we evaluated the cut-off frequency of the filter-based fatigue index using surface electromyography (EMG) signals from different upper and lower extremity muscles under different exercise conditions. Twenty seven subjects participated in isotonic knee extension exercises, fourteen subjects in isotonic elbow flexion and isokinetic knee extension exercises, and twenty subjects in isometric knee extension, isotonic ankle dorsiflexion, and isotonic elbow extension exercises. EMG signals were obtained from right rectus femoris (RF), vastus medialis (VM), vastus lateralis (VL), biceps brachii (BB), triceps brachii (TC), and tibialis anterior (TA) muscles during exercises. The filter-based fatigue index was compared with sEMG-based fatigue indices such as mean root-mean-square (RMS) values, median frequency, Dimitrov spectral index, and Gonzalez-Izal wavelet index. Results showed that optimized cut-off values for all muscles and all exercises approximated to 350 Hz. This implies that the cut-off frequency of 350 Hz is appropriate for general use, showing better determination coefficient with biomechanical fatigues such as joint torques and powers than the other fatigue indices in different muscles during different exercises.