Thenar motor unit number estimation(MUNE) was performed in 49 normal subjects without known neuromuscular diseases using statistical method. The purposes of this study were to compare MUNE parameters between the dominant and non-dominant hands and to evaluate the changes according to age. Reproducibility was assessed in 20 subjects also. The results showed that thenar motor units number, maximum negative peak compound muscle action potential (CMAP) area and mean area of single motor unit potentials(SMUP) were not different between dominant and non-dominant sides, but maximum negative peak CMAP amplitude was larger in dominant than non-dominant side. With aging, the motor unit number, maximum negative peak CMAP amplitude and area decreased and the mean area of single motor unit potentials increased. There was a high reproducibility between the test and the retest values for motor unit number, maximum negative peak CMAP amplitude and area as well as mean area of single motor unit potentials.

The statistical estimate of the motor unit number is a reliable method and easily available in clinical settings. The results of this study are expected to be used as a baseline data for the future.