An astronaut who busies himself on mission matters in space and an unemployed couch-potato may have at least one thing in common: both can suffer from muscle wasting. Muscle wasting, also called atrophy, is defined as the loss of muscle mass. The proteins that form the building blocks of muscles are constantly broken down and constantly repaired or replaced. A dynamic balance normally occurs between the breakdown of proteins and creation of proteins. When proteins break down quicker than they are replaced, wasting results.
Symptoms
The chief symptom of muscle wasting include muscular weakness, decrease of length and bulk of muscle, loss of definition, decrease in range of motion, limited endurance and pain or discomfort during exertion. The onset of symptoms can occur very quickly or take years to develop slowly, depending on the cause of the wasting. Causes can include disuse, nutritional problems or neurological problems. If your symptoms occur unexpectedly or persist, consult your physician.
Disuse Atrophy
When you don't use your muscles, they begin to atrophy quickly. Astronauts begin to lose muscle mass, as well as bone mass, within days of being in a weightless environment. This occurs even when they exercise, so the loss seems to be linked to not having load-bearing weight on their muscles and skeleton.
However, don't count on gravity alone to keep your muscles from wasting. When muscles are immobilized after an injury, they begin to atrophy within three days. Those who are bedridden or have a sedentary lifestyle can experience muscular wasting. Anti-gravity muscles -- muscles that help maintain your posture and you hold you erect -- atrophy faster than the opposing muscles.
Neurological Wasting
Varied neurological conditions can cause or contribute to muscle wasting. Examples of neurological disorders that cause muscle wasting include multiple sclerosis, ALS or Lou Gehrig's disease, polio, Guillain-Barre syndrome and muscular dystrophy. Sometimes these conditions directly disrupt the process of protein synthesis.
For example, the most common forms of muscular dystrophy are caused by a genetic defect that disrupts the creation of the muscle protein dystrophin, the lack of which causes muscle tissue to break down. Neurological wasting may affect all muscles or particular muscle groups and can affect one or both sides of the body. Generally, neurological wasting conditions are progressive; they tend to get worse over time.
Other Causes
Muscular atrophy occurs normally during aging. Some of the wasting happens because of disuse, but it is also a product of other processes. Sarcopenia, age-related loss of muscle mass, function and strength, occurs because of decreases in protein synthesis and hormone levels and changes in the neuromuscular system due to the loss of nerve cells that regulate motor movement.
Nutritional deficiencies and starvation contribute to wasting. The body cannot synthesize the amino acids it needs to replenish muscular proteins. When diets don't provide sufficient protein, muscle wasting occurs. Other conditions that can contribute to muscle wasting include osteoarthritis, spinal cord injury, stroke, motor neuropathy associated with conditions such as diabetes, myopathy associated with alcohol abuse and long-term corticosteroid therapy.
References
- "Massage Today": Understanding Disuse Atrophy; Whitney Lowe, LMT; Oct. 2005
- MedlinePlus: Muscle Atrophy
- "The New York Times"; Muscle Atrophy; Gina Kolata; March 2011
- University of Maryland Medical Center; Muscle Atrophy
- University of New Mexico; Sarcopenia: The Mystery of Muscle Loss; Len Kravitz, Ph.D.
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