Age-related changes in motor unit function

This review focuses on the functional relationship between age-related morphological and physiological changes at the level of the motor unit (MU). It is well established that older humans are weaker than younger people, exhibit reduced force control, and have slower neuromuscular contractile properties. Older people may also exhibit a decrease in MU discharge rate, and an increase in variability of MU discharge at high force levels. The matching of MU discharge and contractile properties may be an age-related neurophysiological strategy adopted to optimize motor control, similar to that observed in acute conditions such as fatigue. Because muscle force output is modulated partially by MU discharge behavior, the study of these properties may offer insights into the physiology of muscular weakness and motor function in older people. In turn, this will allow the implementation of optimal exercise and rehabilitation programs to reduce the degree of dependence associated with aging. (C) 1997 John Wiley & Sons, Inc.