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Aging results in a gradual loss of overall function. Skeletal muscle shows predictable age-related alterations in function. The typical adult will lose muscle mass as they age. This varies according to sex and level of activity. At the cellular level, muscle loses cross-sectional area and fiber number, with type-II muscle fibers being the most affected by aging. Some denervation of fibers also can occur. Combining these factors leads to an increase in type-I fibers in older adults. Metabolically, the enzymes of glycolysis seem to be affected little by aging while aerobic enzymes appear to decline with age. Tension production declines and there is a general “slowing” of the mechanical characteristics of skeletal muscle. In spite of the reduction in function, training can minimize such losses or even reverse some changes. The results of reduced demand placed on muscle as a person ages, and the subsequent loss of function do not seem to be inevitable. Endurance training can improve the aerobic capacity of muscle while resistance training can improve central nervous system recruitment of muscle and muscle mass. To prevent much of the age-related impact on skeletal muscle, a lifetime of physical activity is encouraged.