Muscular atrophy

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Classification according to ICD-10
M62.5 Muscle wasting and atrophy, not elsewhere classified
ICD-10 online (WHO version 2019)

Muscle atrophy or muscle wasting , Latin atrophia musculorum , also amyotrophy (from ancient Greek a "un-", μυς mys "muscle" and τροφή trophie "nourish"), is defined as a reduction in muscle mass . This form of atrophy usually occurs when people are temporarily prevented from performing everyday movements, such as immobilization after an injury or a hospital stay. The atrophy of a muscle goes hand in hand with the muscle weakness, since the strength development of the muscle is directly related to its mass. Modern medicine came to the conclusion that, due to the rapid onset of muscular atrophy when inactive, patients should become physically active as quickly as possible, despite recent treatment.

Muscle atrophy also occurs as a side effect of several diseases such as cancer , AIDS , congestive heart failure , chronic lung disease , kidney failure, and severe burns . For patients who suffer from cachexia in addition to these diseases , the chances of survival drop drastically. In addition, malnutrition ultimately leads to muscle atrophy.

The complete inactivity of muscles, as occurs when muscle tissue is immobilized for several days - for example after a bone fracture (plaster cast) - leads to particularly rapid inactivity atrophy. Keeping this as low as possible is one of the main tasks of physiotherapists who work in collaboration with hospitals and orthopedists . In fracture patients who have been immobilized for three weeks, the atrophy of the back and gluteal muscles will be so advanced during rehabilitation that even sitting without assistance is much more difficult and also causes pain, stress and exertion, even after just a short period of ten minutes.

Neurogenic atrophy has a similar effect. Damage to nerves that stimulate the muscle leads to this form of atrophy and causes stunting in an otherwise healthy limb . Furthermore, muscles will atrophy in weightlessness after a certain period of time without training. This is partly due to the less effort required to move.


If everyday movements, such as walking, climbing stairs, cycling or doing simple housework, are more difficult than usual, this can be due to insufficient or non-existent stress beforehand. The risk of falling or performing incorrect movements with such simple movements and of causing additional injuries increases the longer the period of inactivity. Older people are a particularly threatened group of society.


Muscle atrophy can be caused in different ways:

Due to the reduced strength of the muscles ( muscle hypotonia ), pain can occur even with low stress.


Determination of quantity

By computed tomography muscle tissue can vary from other tissues can be distinguished and thus the muscle percentage to be determined in the body.

Rapid loss of muscle tissue can be recognized by the amount of urea in the urine . The equivalent nitrogen content (in grams) of the urea (in mmol) can be estimated using the conversion factor 0.028 g / mmol. Furthermore, 1 gram of nitrogen is roughly equivalent to 6 grams of protein and 1 gram of protein is roughly equivalent to 4 grams of muscle tissue. Accordingly, 1 mmol of nitrogen in the urine (measured using the urine volume in liters multiplied by the urea concentration in mmol / l) would correspond to a muscle loss of 0.67 grams.

Differential diagnosis

With age, the ability to maintain skeletal muscle function and mass gradually decreases . The exact cause of this condition, which is called " sarcopenia ", is still unknown. Sarcopenia could be related to a combination of the successive failure of the “ satellite cells ”, which are responsible for the regeneration of skeletal muscle fibers , and a reduced sensitivity to growth factors , which are required for the maintenance of muscle mass and the survival of satellite cells.

In addition to the simple loss of muscle mass (atrophy) and the age-related reduction in muscle function (sarcopenia), there are other diseases that can be caused by structural defects in the muscle (muscle wasting) or by inflammatory reactions of the body against the muscle ( myopathies ).


Inactivity and malnutrition lead to atrophy of the skeletal muscles in mammals . In addition, there is a smaller number and size of the muscle cells, as well as a smaller protein content. In humans, longer phases of immobilization, for example through bed rest or weightlessness, lead to muscle weakness and atrophy. Such consequences have also been observed in small mammals in hibernation, such as the golden-mantled ground squirrel and the bats .

Bears are an exception to this rule; Species in the Ursidae family are known for their ability to survive long periods of hibernation in adverse environmental conditions with low temperatures and limited food availability. During this time, bears migrate through various psychological, morphological, and behavioral changes. Your ability to maintain skeletal muscle number and size during a period of inactivity is of significant importance.

During hibernation, bears can endure four to seven months of inactivity and anorexia without muscle atrophy and protein loss. There are a few known factors that favor muscle tissue maintenance. During the summer months, bears take advantage of the availability of food and accumulate muscle protein. During inactivity in the winter months, the protein balance is maintained by less protein breakdown. In times of immobility, the bears' muscle breakdown is also suppressed by a proteolytic inhibitor that is released in the circulation. Another factor that helps maintain muscular strength in hibernating bears is the occurrence of periodic voluntary and involuntary contractions from tremors during torpor . The three to four daily phases of muscle activity are partly responsible for maintaining muscle strength and responsiveness during the hibernation of the bears.

See also

Web links

Individual evidence

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