Design and evaluation of a new filter-based fatigue index

Abstract

In this study, new filter-based fatigue index was designed to estimate muscle fatigue.Muscle fatigue is a temporary loss of strength and energy resulting from hard physical work. It is a hindrance during exercise, as it causes dysfunction. Thus muscle fatigue plays an important role in prolonged contractile activity-induced skeletal muscle injury. Because of these reasons, the measurement of muscle fatigue is very important.Filter-based fatigue index, which is the ratio of high-frequency to low-frequency components of EMG power, was designed to assessing muscle fatigue. To determine the frequency bandwidth of the designed fatigue index, cut-off frequencies of the high-pass-filter were optimized to maximize the correlation coefficient between the peak power or joint torque and the designed filter-based fatigue index. To evaluate the designed filter-based fatigue index, accuracy of muscle fatigue estimation was compared with other fatigue indices. The designed fatigue index was validated in various muscles, different exercises, and different inter-electrode distances. Results, The filter-based fatigue index showed the best correlation with biomechanical fatigue over other fatigue indices in all conditions. This implies the filter-based fatigue index could assess muscle fatigue accurately than other fatigue indices. In addition, optimized cut-off frequencies in various muscles, under different exercises and various inter-electrode distances were consistent about 350 Hz. Consistency of the optimized cut-off frequencies in all conditions implied that 350Hz HPF could be a general solution for the filter-based fatigue index and the filter-based fatigue index reflects firing rate of motor units. Overall, these findings may be useful for muscle fatigue assessment.One of the main finding of this study was that filter-based fatigue index reflects the firing rate of motor units. However, firing rates of motor units were not measured during fatigue. In further studies, MUAP decomposition methods or intramuscular EMG methods would be applied to measure the firing rate of motor units.