Symptom · Whole body
Weakness
Also known as: muscle weakness, loss of strength
Loss of muscle power, distinct from tiredness or heaviness. True weakness means a muscle cannot do what it could before, and its pattern (one side, one limb, both legs, face and eyes, or everywhere) points to the brain, spinal cord, nerve, junction or muscle.
What it is
Loss of muscle power, distinct from tiredness or heaviness. True weakness means a muscle cannot do what it could before, and its pattern (one side, one limb, both legs, face and eyes, or everywhere) points to the brain, spinal cord, nerve, junction or muscle.
Common causes
Deconditioning, illness and ageGeneralised weakness after bed rest, infection or with muscle loss in older age.
Nerve compressionFoot drop from a slipped disc, wrist weakness from radial nerve pressure, hand weakness from carpal tunnel or ulnar nerve entrapment.
Bell's palsySudden weakness of one side of the face including the forehead.
Low potassium, thyroid disease, steroidsGeneralised or proximal weakness (difficulty rising from a chair, lifting arms).
Statin and other drug-induced myopathyAching weak thighs and shoulders.
Less common causes
Stroke and TIASudden weakness of the face, arm or leg on one side.
Spinal cord compressionWeakness of both legs with numbness and bladder problems.
Guillain-Barre syndromeAscending weakness over days, can affect breathing.
Myasthenia gravisFatigable weakness: drooping eyelids, double vision, worse as the day goes on.
Motor neurone disease and muscular dystrophiesProgressive weakness with wasting or twitching.
Multiple sclerosisEpisodes of weakness, numbness or vision loss.
Often occurs with
Seek urgent care if
- Sudden weakness of the face, arm or leg, especially on one side: call emergency services (stroke)
- Weakness of both legs, or weakness with loss of bladder or bowel control
- Weakness that spreads over hours or days, or affects swallowing or breathing
- Weakness after a head, neck or back injury
Conditions to read about
StrokeHerniated (slipped) discUnderactive thyroid (hypothyroidism)Overactive thyroid (hyperthyroidism)Parkinson's disease
How it is investigated
Educational content. This page explains what a symptom can mean so that the anatomy and the medical reasoning make sense. It cannot tell you what is causing yours: only a clinician who can examine you and order tests can do that.