Muscle atrophy refers to the wasting or loss of muscle tissue resulting from disease or lack of use.

There are two types of muscle atrophy.

Disuse atrophy occurs from a lack of physical exercise. The majority of muscle atrophy in the general population results from disuse. Persons with sedentary jobs, with medical conditions that limit movement, or who have decreased activity levels can lose muscle tone and develop atrophy. This type of atrophy can be reversible with vigorous exercise.

Bed-ridden people can undergo significant muscle wasting. Astronauts, free of the gravitational pull of Earth, can develop decreased muscle tone and loss of calcium from their bones following just a few days of weightlessness.

The most severe type of muscle atrophy is neurogenic atrophy. It occurs when there is injury or disease to a nerve. This type of muscle atrophy tends to occur more suddenly than disuse atrophy.

Examples of diseases affecting the nerves that control muscles would be poliomyelitis (polio), amyotrophic lateral sclerosis (ALS or Lou Gehrig's disease), and Guillain-Barre syndrome.

Even minor muscle atrophy usually results in some loss of mobility or power.

Some atrophy occurs normally with aging. Other causes may include:

• Amyotrophic lateral sclerosis (ALS or Lou Gehrig's disease)
• Burns
• Diabetic neuropathy
• Guillain-Barre syndrome
• Injury
• Long-term corticosteroid therapy
• Long-term immobilization
• Muscular dystrophy
• Osteoarthritis
• Rheumatoid arthritis
• Peripheral neuropathy
• Polio
• Spinal cord injury
• Stroke

An exercise program (under the direction of a therapist or doctor) is recommended along with whirlpool baths and other types of rehabilitation.

Exercises using braces or splints are recommended for those who cannot actively move one or more joints.