Skeletal muscles from which the propagation of motor unit action potentials is detectable with a surface electrode array

Motor unit action potentials (MUAPs) propagate bidirectionally along the muscle fibers. Whether or not the propagation of MUAPs can be detected with surface electrodes depends on the configuration of muscle fibers and innervation zones. The authors clarified the muscles from which the propagation of MUAPs is detectable with a surface electrode array placed along the muscle fibers. Twenty-six typical muscles in the arm, leg, trunk, neck and face were investigated under voluntary contraction, and in 19 muscles the propagation of MUAPs was detected. In these muscles the source of the bidirectional propagation marked the position of innervation zones. In the other 7 muscles, the propagation of MUAPs was not detected or was detected only under weak contraction.