muscle wasting
Meaning of muscle wasting: Muscle shrinking because it is not being used, not being fed, or is being broken down faster than the body rebuilds it.
Definition of muscle wasting
Muscle wasting is the loss of muscle bulk and strength, seen as limbs that look thinner and feel weaker than before. It happens when the rate at which muscle protein is broken down outpaces the rate at which it is rebuilt. Long periods of bed rest, poor nutrition, nerve damage, chronic illness and ordinary aging are the usual drivers.
What causes muscle to shrink?
| Cause | What it looks like |
|---|---|
| Disuse, such as a cast or bed rest | Rapid loss in the affected limb, largely recovered with activity |
| Loss of nerve supply | Marked wasting with twitching under the skin, following the nerve territory |
| Cachexia in cancer, heart failure or lung disease | Weight and muscle fall together, and eating more does not reverse it |
| Sarcopenia of aging | Slow, widespread loss of both bulk and power |
| Inherited muscle disease | A set pattern of weakness, often starting in childhood |
How is it different from losing weight?
Weight is a single number that hides what has been lost. A person can shed fat while muscle holds steady, or keep a stable weight while muscle quietly gives way to fat. Someone with obesity can be wasting badly, which is why BMI alone misses it. Grip strength, the ability to rise from a chair without using the arms, the circumference of the upper arm, and imaging that separates muscle from fat all give a truer picture. Loss of muscle is measured in function as much as in bulk.
Why does it matter?
Muscle is not only for movement. It is the body's largest store of protein, drawn on during illness, and it steadies the joints that keep a person upright. Wasting brings falls and fractures, slower recovery from surgery or infection, and poorer tolerance of demanding treatment. When the muscles that drive breathing and swallowing are affected, chest infections follow. In some inherited conditions the process is hereditary and progressive, while in disuse and undernutrition it is often partly reversible once the cause is addressed.
Also known as
Used in a sentence
Examination showed muscle wasting of the right thigh after six weeks in a cast.
Good to know
Muscle wasting can be hidden by a stable or rising body weight, because fat replaces the lost muscle, so strength and function reveal it earlier than the scale does.