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Sarcopenia -- The Loss of Muscle Mass and Function
E-Newsletter No. 14
Sarcopenia, the loss of muscle mass and function, is an important consequence of aging. The prevalence of sarcopenia, depending on the definition used, varies from 10% to 30% in men over the age of 60, and women over the age of 30. The principle component of the decrease in fat-free mass is in the loss of muscle mass; there is little change in non-muscle lean mass.
Between 20 and 80 years of age, the cumulative decline in skeletal muscle mass amounts to 35%-40%. The depletion of muscle mass does not result in weight loss because of the corresponding accumulation of body fat.
The loss of muscle mass results from a decrease in the number as well as a cross-sectional area of muscle fibers. There is a preferential atrophy of fast twitch, type II fibers. There is an increase in intramuscular fat and connective tissue. These changes reduce the contractile tissue volume available for locomotion and metabolic functions. Aging is associated with decreased synthesis of skeletal muscle proteins, and attenuated myosin heavy chain and actin synthesis rates, which are important also for adenosine triphosphate (ATP) generation of high-energy phosphate bonds for mechanical energy.
The loss of muscle mass that occurs with aging is associated with a reduction in muscle strength and power between 50 and 70 years of age, due primarily to muscle fiber loss and selective atrophy of type II fibers. Loss of muscle strength is even greater after the age of 70; 28% of men over the age of 74 can not lift objects weighing more than ten pounds over their heads. With increasing age, there is a progressive reduction in muscle power, the speed of strength generation, and fatigability: the ability to persist in a task.
Loss of muscle mass and strength leads to impairment of physical function, as indicated by the impaired ability to arise from a chair, climb stairs, generate gait speed, and maintain balance. The impairment of physical function contributes to loss of independence, depression, dependency, and increased risk of falls and fracture in the elderly.
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