Reference values for the motor unit number index and the motor unit size index in five muscles.

Abstract

Few reference values have been established for the motor unit number index (MUNIX) and motor unit size index (MUSIX). In this study we aimed to investigate the features of MUNIX in healthy individuals for five muscles. We measured the MUNIX in the right abductor pollicis brevis (APB), abductor digiti minimi (ADM), biceps brachii (BB), tibialis anterior (TA), and trapezius (TR) muscles. The study enrolled 76 male and 74 female participants. The mean MUNIX and mean MUSIX of the right APB, ADM, BB, TA, and TR muscles were 191.0 ± 43.6, 179.1 ± 38.8, 179.7 ± 36.2, 152.1 ± 38.8, and 166.1 ± 40.7; and 60.4 ± 12.5, 59.3 ± 13.7, 43.8 ± 11.5, 41.3 ± 10.7, and 49.1 ± 15.2, respectively. MUNIX in these five muscles was inversely related to age. The establishment of reference values for MUNIX and MUSIX in five muscles may help in monitoring the progression of neuromuscular diseases.