STATUREAND MUSCULOSKELETAL FUNCTION

Aging is accompanied by a progressive decline in height, especially among older women. This decline in height is attributed mainly to compression of the spinal column. Body composition changes as well. The amount of fat in­creases, and lean body mass and total body water decrease with advancing age.

With aging, there is a reduction in muscle size and strength that is related to a loss of muscle fibers and a re­duction in the size of the existing fibers. Although the de­cline in strength that occurs with aging cannot be halted, its progress can be slowed with exercise. There is a decline in high-speed performance and reaction time because of a decrease in type II muscle fibers.¹²,¹³ Impairments in the ner­vous system also can cause movements to slow. However, type I muscle fibers, which offer endurance, are thought to remain consistent with age (see Chapter 12).

Numerous studies have reported a loss of bone mass with aging, regardless of sex, race, or body size. With aging, the process of bone formation (i.e., renewal) is slowed in relation to bone resorption (i.e., breakdown), resulting in a loss of bone mass and weakened bone structure. This is especially true for postmenopausal women. By 65 years of age, most women have lost two thirds of their skeletal mass owing to a decrease in estrogen production.¹³ Skele­tal bone loss is not a uniform process. At approximately 30 years of age, bone loss begins, predominantly in the tra-becular bone (i.e., fine network of bony struts and braces in the medullary cavity) of the heads of the femora and radii and in the vertebral bodies.¹³,¹⁴ By 80 years of age, women have lost nearly 43% of their trabecular bone, and men have lost 27%. This process becomes pathologic (i.e., osteoporosis) when it significantly increases the pre­disposition to fracture and associated complications (see Chapter 58).

The prevalence of joint disease is increased among the elderly. By age 65 years, 80% of the population has some articular disease. Osteoarthritis is so common among elderly persons that it is often incorrectly assumed to be a normal age-related change rather than a disease. The sy-novial joints ultimately are affected by osteoarthritis, most commonly the joints of the hands, feet, knees, hips, and shoulders. It is characterized by cartilage loss and new bone formation, accounting for a distortion in articula­tion, limited range of motion, and joint instability (see Chapter 59). Age is the single greatest risk factor for devel­opment of osteoarthritis, in part because of the mechani­cal impact on joints over time, but it also is related to injury, altered physical condition of the articular cartilage, obesity (e.g., knee), congenital deformity (e.g., hip), crystal deposition in articular cartilage (e.g., knee), and heredity. Pain, immobility, and joint inflammation often ensue. Treatment is aimed at minimizing risk factors, weight loss if indicated, exercise to increase muscle strength, and pain relief measures.