title: A method for estimating the number of motor units in thenar muscles and the changes in motor unit count with ageing.
abstract: A method for estimating the number of motor units in median innervated thenar muscles is described. In normal human subjects under 40 years of age, the mean and 1 SD was 253+34. The number of motor units falls with increasing age, especially after mid life, so that elderly subjects often have less than one-half the number in youth despite good strength. The cause is not known but probably includes peripheral nerve trauma and `primary neuronal cell death'.
mesh_terms: D000200:Action Potentials; D000293:Adolescent; D000328:Adult; D000368:Aged; D000375:Aging; D004558:Electric Stimulation; D005260:Female; D006801:Humans; D008297:Male; D008475:Median Nerve / Q000033:anatomy & histology*; D008875:Middle Aged; D009046:Motor Neurons; D009132:Muscles / Q000033:anatomy & histology*; D009410:Nerve Degeneration; D009431:Neural Conduction