As one gets older, the mass of skeletal muscle diminishes throughout the body. The muscles atrophy which results in a decreased number of muscle fibres as well as a decrease in the size of the remaining fibres. As skeletal muscles are postmitotic they are not able to reproduce to produce new fibres. As a result the fibres are switched out with fat tissue.
The muscle fibre loss has been reported to be as high as 30% between the ages of 30 and 80 years. Correct nutrition and exercise may slow the loss muscle cells; however heredity also seems to be a factor.
Together with the loss of skeletal muscle mass comes the loss of skeletal muscle strength. For most individuals there is only a 10 to 20% reduction in strength up to the age of 70. After the age of 70 the reduction in strength may increase to 50%. More severe muscle loss (which is called sarcopenia, which literally means loss of flesh) is as a result of disease or extreme inactivity and not from ageing alone.
What Is Muscle Decline Caused By?
Some of the reduction is caused by physical inactivity as well as decreasing levels of growth hormone and testosterone, which are responsible for stimulating muscle development. In addition, muscles are not able to contract as quickly because more fast-contracting (fast-twitch) muscle fibres are lost as opposed to slow-contracting (slow-twitch) muscle fibres.
Most older people retain sufficient muscle mass and strength for all required tasks. A lot of older people remain strong athletes. They compete in sports and enjoy vigorous physical activity. But, even the fittest notice some decline as they age.
What Age-Related Changes Take Place In Muscle?
Muscle drops size and strength as we age, which can contribute to fatigue, weakness as well as reduced tolerance to exercise. This is as a result of a number of factors working in combination. These include:
- Muscle fibres reducing in number and shrinking in size.
- Muscle tissue is replaced more slowly. Lost muscle tissue is substituted with a tough, fibrous tissue.
- Alterations to the nervous system cause muscles to have diminished tone and ability to contract.
What Is Sarcopenia?
Sarcopenia is a condition that is characterised through loss of skeletal muscle mass and function.
Symptoms of sarcopenia may include weakness and loss of stamina. This can interfere with physical activity. Reduced activity shrinks muscle mass further. Although sarcopenia is demonstrated mostly in people who are not active, the fact that it also is seen in people who stay physically active suggests that there are other factors in its development. Researchers are of the belief that these include:
- Reduction in nerve cells which are responsible for sending signals from the brain to the muscles to begin movement
- Lower concentrations of some hormones in addition to growth hormone, testosterone, and insulin-like growth factor
- A reduction in the ability to turn protein into energy
- Not getting sufficient calories or protein each day in order to sustain muscle mass
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