Motor-unit estimation: the beginning.

Motor unit estimation in human subjects was conceived in 1967 and was first performed on the extensor digitorum brevis muscle, using a technique of incremental motor nerve stimulation. Losses of motor units were found in elderly control subjects and, surprisingly, in some patients with muscular dystrophy. The pathophysiological basis for the latter observations remains unexplained. Other motor unit studies at that time included the first recordings of single motor unit twitches. The recent development of a software programme for motor unit estimation is a significant advance in that it deals with the problem of "alternation" and eliminates subjectivity. Also of importance has been the introduction, by other workers, of alternative ways of sampling motor unit potentials. It is likely that the field will continue to be active and will benefit from the availability of more powerful computers and more stringent software programmes.