Muscle atrophy is actually a symptom that is caused either by inactivity, poor nutrition or by other illnesses that adversely affect the nerves in the muscles. Examples of medical conditions that affect the nerves in the muscles include amytrophic lateral disease, also known as ALS or Lou Gehrig's disease, Guillain-Barre syndrome, poliomyelitis and neuropathy, according to the National Institutes of Health.
Muscular atrophy is a term that refers to the loss or the wasting away of muscle tissue. Physical inactivity is one of the two common causes of muscular atrophy. The inactivity may be due to an individual's work such as having to stay seated for most of the working hours. Inactivity may also be as a result of having a medical condition that restricts an the mobility of an individual, such as when recovering from an accident.
Poor nutrition can also cause the muscles to waste away. Once the body senses that it is deprived of nutrients from food, it turns on its fat stores, as well as the muscle tissues. Starvation is one of the clear examples that cause muscular atrophy, such as in the cases of prisoners of war.
Malabsorption can also lead to poor nutrition and it is the inability of the intestines to absorb essential nutrients. Celiac disease, allergy to dairy products and cystic fibrosis are listed by Healthline as medical conditions that cause malabsorption.
Apart from those already mentioned, Healthline lists multiple sclerosis, AIDS, hypercalcemia, osteomalacia and type 2 diabetes as other diseases that affect the nerves.