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Deterioration of skeletal muscle and its neural inputs begins between the ages of 50 and 60 years. Much of deterioration of skeletal muscle observed may actually be a result of inactivity, rather than age itself.

Anatomy

Limitation in the range of motion of different joints is a frequent finding in older persons. This may be a result of joint incongruity, capsular and ligamentous contracture, or loss of elasticity in tendons. All of these processes may affect force development by modifying the leverage component of the length-tension relationship.

Muscle strength

Muscle strength appears to be relatively stable through 50 years of age. A 15% loss in muscle strength per decade occurs between the ages of 50 and 70 years of age. From the ages of 70-80 years, a 30% loss in muscle strength has been noted. Clinically, one observes a decreased ability to engage in physical activity in older persons due to decreased muscle strength.

The decline in muscle strength may have important functional consequences. The decline in strength in muscles of the lower extremities may be associated with gait disorders, falls, and hip fractures. A reduction in upper body strength increases the risk of accidents in activities which require lifting, pushing, or pulling maneuvers (such as housekeeping, cooking, and eating). Weakness of low back muscles may be related to problems such as disk herniation and chronic low back pain of soft tissue origin.

The decline in muscle strength with aging may be attributed to the loss of muscle mass (decrease in skeletal muscle fiber number, decrease in muscle fiber size), to some alteration of the muscle's capacity to generate force (recruitment of skeletal muscle fibers, force/cross-bridge), or to a combination of these two mechanisms, thus making older muscle intrinsically weaker. Men, from 24-80 years, lose approximately 40% of total skeletal muscle mass. Total muscle cross-sectional area peaks at the age of 24 years. From 24-50 years of age, 10% of the total muscle cross-sectional area is lost. Thereafter, muscle atrophy is accelerated so that between 50 and 80 years of age, an additional 30% of total muscle cross-sectional area is lost. The decline in muscle mass may account, in part, for the decline in muscle strength seen with aging. Interestingly, postural muscles, such as the quadriceps and soleus, show age-related atrophy to a greater extent than non-postural muscles.

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