Effects of Aging

From about age 30, the density of bones begins to diminish in men and women; this loss of density accelerates in women after menopause. As a result, the bones become more fragile and are more likely to break (see Section 5, Chapter 60), especially in old age.

As people age, their joints are affected by changes in cartilage and in connective tissue. The cartilage inside a joint becomes thinner; components of the cartilage (the proteoglycans) become altered, which may make the joint less resilient and more susceptible to damage. Thus, in some people, the surfaces of the joint do not slide as well over each other as they used to. This process may lead to osteoarthritis (see Section 5, Chapter 66). Additionally, joints become stiffer because the connective tissue within ligaments and tendons becomes more rigid and brittle. This change also limits the range of motion of joints.

Sarcopenia is a process that starts around the age of 30 and progresses throughout life. In this process, the amount of muscle tissue and the number and size of muscle fibers gradually decrease. The result of sarcopenia is a gradual loss of muscle mass and muscle strength. Fortunately, the loss in muscle mass and strength can partially be overcome or at least significantly delayed by regular exercise. The types of muscle fibers are affected by aging as well. Certain muscle fibers contract faster than others, and with age the number of these fibers decreases much more so than the number of the slower type. Thus, muscles are not able to contract as quickly in old age.