MMG PSD evolution in time (subject E): Biceps muscle. The evolution in time of the Biceps muscle MMG PSD is shown in contour plot, computed to display at 15 levels the isolines of the matrix containing the succession of the spectra, from the beginning to the end of the contraction (black – zero level; red, yellow – higher PSD peaks). The PSD compression towards lower frequency and higher PSD peaks by the end of contraction, are noticeable. The middle trace (blue) shows the MMG MF evolution; MF decreases with increasing fatigue, thus proving the PSD compression. The lower trace shows the MMG RMS evolution; RMS increases with increasing fatigue.