LONGITUDINAL-STUDY OF THE CONTRACTILE AND ELECTRICAL-PROPERTIES OF SINGLE HUMAN THENAR MOTOR UNITS

Serial motor unit number estimates have shed important light on the ex tent and rates of motoneuron losses in aging and amyotrophic lateral s clerosis. However, the estimates alone provide few clues to the health and functional status of surviving motor units. A reliable means for assessing the functional status of the surviving motor units would the refore by a welcome addition to our present tools for studying motor u nits. Examining the physiological properties of samples of motor units drawn at intervals during the course of a motoneuronal disease suffer s from the important limitation that the samples may not be representa tive of one another. The latter problem could be circumvented by seria lly studying the same motor units. This study describes a noninvasive technique capable of longitudinally tracking the contractile and elect rical properties of specific single thenar motor units in healthy subj ects, in some instances over several years. The technique proved to be reasonably reliable and provided information on a wide range of contr actile and electrical properties of motor units. Such an approach coul d serve as a potentially powerful and sensitive means of studying the life histories of single motor units in aging, diseases of the motoneu ron, and in the latter instances, the responses of the motoneurons to treatment. (C) 1998 John Wiley & Sons, Inc.