New frontiers for muscle function investigation: Integration of surface EMG and 3D ecographic images

Muscle architectural changes, induced by changes in joint position, can influence the amplitude distribution of surface electromyograms (EMGs). By combining grids of electrodes, ultra sound (US) imaging and three-dimensional (3D) kinematics, the relative contribution of different anatomical factors (e.g., pinnation angle, muscle thickness) on EMG features may be quantified. The aim of this paper was to explore the potentiality of this technique in the analysis of how much muscle architectural changes, induced by changes in joint position, can influence the EMG amplitude distribution. While provided with EMG visual-feedback, a participant was asked to recruit a single motor unit of the right tibialis anterior (TA) muscle at two different ankle positions. Surface EMGs, kinematic data and US images were acquired. The spatial distribution of the amplitude of motor unit action potentials was assessed from EMGs. Ankle angles were obtained from 3D kinematics. TA width and thickness variations between the two ankle positions were obtained through the segmentation of US images reconstructed in 3D space. When compared with ankle at plantar flexion, ankle at neutral position resulted in greater TA width and thickness, as well as, in more widely distributed EMG amplitude. These results suggest TA architecture may markedly affect the amplitude distribution of surface EMGs.