Physiological aspects of MMG and EMG spectra during load-varying isometric dorsiflexion

The aim of the study was to examine spectral features of the mechanomyogram (MMG) and electromyogram (EMG) during static and load-varying isometric dorsiflexion to characterize force control strategies of the tibialis anterior. Twelve healthy subjects performed two motor tasks including 1) four exertion levels of static isometric dorsiflexion and 2) load-varying isometric dorsiflexion while tracking a target quasi-sinusoidal curve of three different amplitudes. Generally speaking, for both static and load-varying isometric contractions, the mean frequency of MMG-EMG cross spectra (MMG-EMG MF) progressively increased with effort level, whereas the median frequency of EMG auto spectra among higher effort levels remained unchanged. The MMG-EMG MF versus EMG root mean square regression slope was significantly larger for load-varying isometric contraction than for static contraction control measurements. These findings highlight effort-dependent and task-specific rate coding for force regulation of the tibialis anterior.