Pulse train frequency demodulation by a muscle-load system

An important question in motor control is how low-pass filtering by a muscle-load system is divided between the active state process and muscle-load mechanics. The authors obtained the frequency response of a muscle-load system (treated as a single motor unit) using a low-rate pulse-train stimulus. Load acceleration twitches were detected and RMS displacements calculated from power spectra. Frequency response and other mechanical data indicate third-order, linear mechanics, in combination with active state pulses of about 20-ms duration. Comparable results were obtained for an intact muscle-limb system of man, using RMS displacements and surface EMG amplitude ratios obtained at different frequencies of voluntary oscillation.<>