Muscle function at the motor unit level: Consequences of aging

This review discusser the physiologic age-related changes in both contracti le and neural aspects of the motor unit (MU), summarizing mainly studies on human muscles. The substantial weakness. slowed movements, and reduction i n force control seen in old age cannot be accounted for, solely by loss of muscle mass. Factors such as changes in contractile quality, specific tensi on, and neurologic mechanisms must be considered. The only commonality to d ate is that loss of neuromuscular function is specific to the muscle group. the task, history of use, and possibly gender. Since there is a functional relation,hip between contractile and neural properties of the MU, these as pects need to be studied together and their age-related changes evaluated a nd correlated to better understand neuromuscular weakness with age. Althoug h there are many reports of the positive benefits of strength training for aged humans, the relative contributions of the different aspects of the;MU to improved function are not well understood. One goal in this field is to better understand the mechanisms associated with strength improvements in o rder to develop the most appropriate rehabilitation programs for aged human s.