Discrimination of different motor units by spike-triggered averaging of surface electromyograms.

An objective method was sought for the discrimination of individual motor units (MUs). Discrimination using the conventional needle electrode recording is difficult because the waveforms are easily changed by slight shifts of the electrode. A surface EMG recording was combined with the needle recording and MU activities were obtained by MU-triggered averaging of the surface EMGs. Waveforms of surface MU potentials were stable, irrelevant to changes in recording conditions of needle electrodes and thus were found useful for the purpose of discrimination. Efficacy of this method was tested in the MUs with known axonal conduction velocities.