The amount of muscle tissue (muscle mass) and muscle strength starts to decrease beginning around age 30 and continuing throughout life. Some of the decreases are caused by decreasing levels of growth hormone and testosterone, which stimulate muscle development. Muscles cannot contract as quickly because more fast-contracting (fast-twitch) muscle fibers are lost than slow-contracting (slow-twitch) muscle fibers. Aging’s effects reduce muscle mass and strength by around 10 to 15% during an adult’s lifetime. More severe muscle loss (called sarcopenia, which literally means loss of flesh) results from disease or extreme inactivity, not from aging alone.
Most older people retain enough muscle mass and strength for all necessary tasks. Many older people remain strong athletes. They compete in sports and enjoy the vigorous physical activity. However, even the fittest notice some decline as they age.
Regular exercise to strengthen muscles (resistance training) can partially overcome or significantly delay loss of muscle mass and strength. In the muscle-strengthening exercise, muscles contract against resistance provided by gravity (as in sit-ups or push-ups), weights, or rubber bands. If this type of exercise is done regularly, even people who have never exercised can increase muscle mass and strength. Conversely, physical inactivity, especially bed rest during an illness, can greatly accelerate the loss. During periods of inactivity, older people lose muscle mass and strength much more quickly than younger people do. For example, to make up for the muscle mass lost during each day of strict bed rest, people may need to exercise for up to 2 weeks.
By age 75, the percentage of body fat typically doubles compared with what it was during young adulthood. Too much body fat can increase the risk of health problems, such as diabetes. The distribution of fat also changes, changing the shape of the torso. A healthy diet and regular exercise can help older people minimize increases in body fat.