Muscle atrophy
Many older people have muscular atrophy. Muscle atrophy can also happen to people with certain diseases or medical conditions, like cancer, AIDS, congestive heart failure, Chronic obstructive pulmonary disease, and renal failure (where the kidneys do not work correctly).  Muscles can atrophy (or get smaller and weaker) when those muscles are not used as much as usual - for example, when a person has to wear a cast for a broken arm or leg, or when a person must be on bed rest for a long time during a long illness.  Muscle atrophy can also be caused by Dejerine Sottas syndrome, cachexia, burns, liver failure, and starvation.