The distribution and propagation pattern of motor unit action potentials studied by multi-channel surface EMG.

We developed the multi-channel surface EMG system using a matrix-type of surface electrode and with the aid of digital signal processing. The subjects were 14 normals (4-50 years) and 2 patients with Duchenne muscular dystrophy (7 and 8 years). The biceps brachii and the tibialis anterior muscles were investigated. The location of the motor end-plates and the measurement of muscle fiber conduction velocity were evaluated by the time shift of bipolar EMG arrays along muscle fibers, or by the distribution map of averaged motor unit action potentials (MUAPs). The lateral extension of a motor unit could be also estimated from the changes of averaged MUAP's amplitudes in the distribution map. Moreover in the biceps of 2 patients with Duchenne dystrophy, the mean muscle fiber conduction velocities were reduced compared to normal subjects, and characteristic propagation patterns of action potentials were obtained. In the 2-dimensional or 3-dimensional distribution map of integrated monopolar EMGs, the high density area agreed with the motor end-plate band.