Experimental and analytical investigations of motor unit location for the precise estimation of muscle force with surface electromyograms

Surface motor unit action potential (SMUAP) is generated from a motor unit (MU) located at certain depth from the skin surface. The depth is referred to as MU location in the present papers. The MU location affects the amplitude of MUAP, and smoothed rectified electromyograin (SR EMG) is used to estimate for the muscle force. The aim of this study is to investigate MU locations in the short head of biceps brachii (BIC) and the first dorsal interosseous (FDI), experimentally and analytically with eight-channel surface EMGs (SEMGs) in isometric voluntary contractions. In order to estimate the MU location, profiles of peak SMUAP at each channel were compared with those of different MU locations obtained from the tripole current source model. From the result, MU locations of BIC distributed in a certain range, and those of FDI seemed to be identical. Our method was practical and useful for estimating the approximated MU location.