THE EFFECTS OF AGING AND TRAINING ON SKELETAL-MUSCLE

Aging results in a gradual loss of muscle function, and there are pred ictable age-related alterations in skeletal muscle function. The typic al adult will lose muscle mass with age; the loss varies according to sex and the level of muscle activity. At the cellular level, muscles l oose both cross-sectional area and fiber numbers, with type II muscle fibers being the most affected by aging. Some denervation of fibers ma y occur. The combination of these factors leads to an increased percen tage of type I fibers in older adults. Metabolically, the glycolytic e nzymes seem to be little affected by aging, but the aerobic enzymes ap pear to decline with age. Aged skeletal muscle produces less force and there is a general ''slowing'' of the mechanical characteristics of m uscle. However, neither reduced muscle demand nor the subsequent loss of function is inevitable with aging. These losses can be minimized or even reversed with training. Endurance training can improve the aerob ic capacity of muscle, and resistance training can improve central ner vous system recruitment of muscle and increase muscle mass. Therefore, physical activity throughout life is encouraged to prevent much of th e age-related impact on skeletal muscle.