sEMG feature analysis on forearm muscle fatigue during isometric contractions

In order to detect and assess the muscle fatigue state with the surface electromyography (sEMG) characteristic parameters, this paper carried out a series of isometric contraction experiments to induce the fatigue on the forearm muscles from four subjects, and recorded the sEMG signals of the flexor carpi ulnaris. sEMG’s median frequency (MDF) and mean frequency (MF) were extracted by short term Fourier transform (STFT), and the root mean square (RMS) of wavelet coefficients in the frequency band of 5–45 Hz was obtained by continuous wavelet transform (CWT). The results demonstrate that both MDF and MF show downward trends within 1 min; however, RMS shows an upward trend within the same time. The three parameters are closely correlated with absolute values of mean correlation coefficients greater than 0.8. It is suggested that the three parameters above can be used as reliable indicators to evaluate the level of muscle fatigue during isometric contractions.