Updated 11 February 2013

Muscle weakness

Uncharacteristic muscle weakness or inability of the muscles to perform normally, relative to that person’s normal ability.



Uncharacteristic muscle weakness or inability of the muscles to perform normally, relative to that person’s normal ability.  The symptom will usually be identified when a person is performing exercise or some muscular activity, such as climbing stairs, or carrying goods.  It is however distinct from the weakness (or tiredness) that many will feel when run-down and fatigued as a result of normal activities.

Other names

Lack of strength, weakness

Possible causes
It must be recognised that true weakness is different from that experienced by people as a result of fatigue, but normal daily activities.  In the case of muscle weakness as a symptom of a disease or condition, there is usually a measurable loss of muscle strength, and possibly a reduction in muscle tone as the muscle begins to waste away.  There are however literally thousands of possible causes for muscle weakness, making diagnosis very difficult.

Because muscle contraction requires a signal from the brain, down the spinal cord, to the muscle, the cause of true weakness may lie anywhere along this chain.  It may thus be metabolic, neurological, toxic or directly muscular.

Some of the more common causes include strokes, brain problems such as tumours, degenerative problems such as multiple sclerosis, and muscular problems such as muscular dystrophies and polymyositis.  A variety of other diseases can cause weakness, including diabetes, Cushing’s syndrome (excess cortisol), Lupus and Guillain-Barré syndrome, to name a few of the thousands of possibilities.


Dependent entirely on the cause of the condition, which must be ascertained first.  For this reason, a diagnosis and the resultant recommended treatment are crucial, which is why muscle weakness that is persistent and unexplained should be treated in consultation with a doctor.

When to see a doctor

A doctor should be seen as soon as muscle weakness becomes a recurring or persistent problem.  If the weakness cannot be explained (as with exercise or a strenuous period of work, for example), and occurs suddenly, then a doctor’s diagnosis should be sought.  Similarly, if muscle weakness is one of many symptoms, a doctor should be seen for treatment of the actual underlying cause of the problem.

What to expect at the doctor

Typically, doctors will perform a detailed patient history to ascertain a full medical picture of the condition.  This includes a time pattern of the symptoms (time-frames, medical history, activity history), quality of the weakness (constant or variable, impact of weakness on daily activity and normal function), location, aggravating factors, and any other relieving symptoms.

The doctor will typically then seek further tests, usually of the blood, to eliminate possible causes.  In some cases, where a neurological cause is possible, MRI or CT scans may be performed, as well as specialised metabolic tests (thyroid, muscle biopsies and so forth).


Again, the treatment is dependent on the diagnosis and varies widely.  For neurological problems, physical therapy may be required, whereas for a metabolic problem, medication may be required.

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