What is Bilateral Weakness?

Bilateral weakness refers to weakness that occurs on both sides of the body, generally in either both arms or both legs. It can also be presented as weakness affecting all extremities, meaning both arms and both legs simultaneously. This is a relatively rare condition, as most neurological disorders typically begin with weakness on one side of the body or the other, with the body being divided vertically rather than horizontally.

The most common cause of bilateral weakness is injury. This can occur either to the spinal cord, muscles in both arms or both legs, or to the spine itself. Often, this is temporary and once the injuries have had proper time to heal, the muscles eventually regain full strength. Sometimes this requires physical therapy to rebuild muscle mass, especially in instances of extended periods of recovery when the muscles have not been used.

Although relatively uncommon, sudden bilateral weakness can be a sign of a serious neurological disorder. Multiple sclerosis, Parkinson’s disease, and Lou Gehrig’s disease are all examples of illnesses in which weakness is a primary symptom. Clinical weakness is a term used to describe muscles that lack strength and are not able to perform tasks which would be easy for the average person.


There is a condition known as perceived bilateral weakness, meaning that the muscles feel weak and fatigued even when there is nothing wrong. This is often a psychological effect which may present itself during times of severe stress or in those who suffer from certain anxiety disorders, primarily hypochondria. The difference between actual and perceived weakness is that in perceived cases, the muscles have not lost strength or tone.

Treatment for severe bilateral weakness will depend on the underlying cause. Tests will likely be run to rule out serious conditions, and the patient may be told to rest his or her muscles in the meantime. Some temporary conditions may be found to cause weakness, including dehydration, fatigue, and some viruses.

During a physical exam, patients may be asked to perform a series of exercises to determine if clinical weakness is actually present. This would be indicated by an inability to perform the exercises, despite making an effort. If clinical weakness is diagnosed, further tests may be conducted to find the cause.


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