The main cause of muscle loss tends to be an overall lack of exercise. For example, people with jobs where they sit at a computer all day will often experience some muscle loss unless they include supplementary exercises. Injuries frequently lead to a weakening of muscle for the same basic reason. Other primary causes of lost muscle include aging, diseases or injuries to the nervous system, and illnesses that directly attack the musculature. Some kinds of loss can be overcome through lifestyle changes or treatments, while others are generally permanent.
When muscles aren’t used, the body gradually allows them to decrease. Individuals who don’t get enough exercise will tend to slowly lose muscle for years and years. It can potentially take a long time for this process to become noticeably severe, but maintaining significant amounts of muscle, like the muscle mass of an athlete, for example, takes fairly constant maintenance. If someone is suffering from this kind of muscle reduction, a more active lifestyle can often be enough to reverse the situation.
As people age, their bodies stop regenerating cells as rapidly. This is what causes many of the outward signs of aging, and it is also responsible for a certain amount of muscle loss. It’s also generally true that people tend to exercise a lot less as they get older, and this helps exaggerate the muscle, reducing effects of aging. If frequent exercise is maintained, older people can avoid a lot of muscle loss.
Injuries tend to cause muscle reduction for a few different reasons. Sometimes injuries simply confine a person to a bed for a certain amount of time, and this can cause muscle loss all over the individual's body. In other cases, an injury may simply cause a person to stop using certain muscles, and this can cause more localized muscle reduction.
Disorders of the nervous system have the potential to cause severe muscle loss. This often happens because the nerves simply stop sending impulses to certain muscles. If the muscles don’t move, they gradually decrease in size for the same reason people who live sedentary lives tend to lose muscle.
There are also diseases that simply cause muscles to decrease by directly destroying muscle tissue. A common example would be the various forms of muscular dystrophy. These kinds of diseases are usually difficult to treat because they are often based on genetic predispositions.