Musculoskeletal System

Just as the cardiovascular and respiratory systems work together, the musculoskeletal, nervous, and sensory systems cooperate in the performance of psychomotor skills. The musculoskeletal system consists of the striped muscles and bones whose purpose is to move the arms, legs, and other mobile organs of the body. The efficiency with which such movement takes place depends on the condition of the muscle cells, the bones, and the joints at which the bones are connected with each other.

Age-related structural changes in the musculoskeletal system include a decrease in the total amount of muscle in body tissue after age 40 and its replacement by fat tissue, an increase in deposits of mineral salts in the bones, a decrease in cartilage around joints, and a decrease in the quantity of synovial fluid in the joints. Muscular tone, strength, flexibility, speed, and stamina decline; the relaxation/contraction time of muscles increases and injured muscles heal more slowly.

Aging is also associated with greater sponginess and fragility of the dense part of the bones, a significant increase in stiffness and pain in the joints of the lower spine, hips, and knees, and fractures of the vertebrae, ribs, and hips. Decreased density and greater porosity of bones, and a consequent tendency to fracture more easily are associated with osteoporosis. In this disorder, which is more common during later life and particularly in older women, there is a gradual long-term loss of bone mass.

Combined with changes in the nervous and sensory systems, age-related decrements in the functioning of the musculoskeletal system lead to one of the most characteristic things about being older—being slower. Figure 2-3 shows that simple reaction time to an auditory stimulus increases appre

Musculoskeletal Changes With Aging

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Figure 2-3 Mean reaction time and movement time as a function of chronological age. (Based on data reported in Fozard, Vercruyssen, Reynolds, Hancock, & Quilter, 1994.)

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Figure 2-3 Mean reaction time and movement time as a function of chronological age. (Based on data reported in Fozard, Vercruyssen, Reynolds, Hancock, & Quilter, 1994.)

ciably with aging in both males and females and that disjunctive (choice) reaction time increases even more. Likewise, muscle strength follows muscle mass in being greatest at around age 25, decreasing to 90% of the maximum by age 45, 75% by age 65, and 55% by age 85. To some extent, these decrements can be compensated for by regular exercise.

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