Statistical (Poisson) motor unit number estimation methodological aspects and normal results in the extensor Digitorum brevis muscle of healthy subjects

Introduction. Among the differents techniques for motor unit number estimation (MUNE) there is the statistical one (Poisson), in which the activation of motor units is carried out by electrical stimulation and the estimation performed by means of a statistical analysis based on the Poisson's distribution. Objectives. The study was undertaken in order to realize an approximation to the MUNE-Poisson technique showing a coprehensible view of its methodology and also to obtain normal results in the extensor digitorum brevis muscle (EDB)from a healthy population. Subjects and methods. One-hundred-fourteen normal volunteers with age ranging from 10 to 88 years were studied using the MUNE software contained in a Viking IV system. Results. The normal subjects were divided into two age groups (10-59 and 60-88years). The EDB MUNE from all them was 184+/-49. Both, the MUNE and the amplitude of the compound muscle action potential (CMAP) were significantly lower in the older age group (p<0.0001), showing the MUNE a better correlation with age than CMAP amplitude (-0.5002 and -0.4142, respectively p<0.0001). Conclusion. Statistical MUNE method is an important way for the assessment to the phisiology of the motor unit. The value of MUNE correlates better with the neuromuscular aging process than CMAP amplitude does.