General
Muscle weakness
A genuine loss of strength in one or more muscles — different from simply feeling tired — which when it comes on suddenly or on one side can be a sign of a stroke and needs emergency assessment.
Education and reference only. This explains the common causes of muscle weakness and the warning signs that need urgent help, in plain language — it is not a diagnosis or a substitute for advice from a clinician. If you feel very unwell or are worried, seek medical help.
Quick answer
What is muscle weakness?
Muscle weakness means a true reduction in the power of a muscle, so that it cannot do what it normally would — lifting an arm, gripping, climbing stairs or rising from a chair. It is important to distinguish this from general tiredness or fatigue, where the strength is there but everything feels like an effort.
- Get urgent help: Call 999 immediately if weakness comes on suddenly, or affects one side of the body, the face, an arm or a leg — use the FAST test, as this may be a stroke. Call 999 for weakness with face drooping, slurred speech, confusion or a severe headache.
- Self-care: New muscle weakness should be assessed rather than managed at home, especially if it is sudden or one-sided.
About muscle weakness
Muscle weakness means a true reduction in the power of a muscle, so that it cannot do what it normally would — lifting an arm, gripping, climbing stairs or rising from a chair. It is important to distinguish this from general tiredness or fatigue, where the strength is there but everything feels like an effort. The pattern of weakness gives vital clues. Sudden weakness, particularly down one side of the body or affecting the face, arm or leg together, is a medical emergency that points to a stroke. Weakness that spreads over hours or days, or that begins to affect breathing or swallowing, is also urgent. Weakness that fluctuates and worsens with use suggests a problem at the nerve-muscle junction, while a more gradual, symmetrical weakness — for example difficulty rising from a chair or lifting the arms — can come from muscle, nerve, hormonal or inflammatory conditions. Any new, unexplained or progressive weakness deserves prompt medical assessment.
When to get help
Call 999 or go to A&E if muscle weakness comes with any of these warning signs:
- Call 999 immediately if weakness comes on suddenly, or affects one side of the body, the face, an arm or a leg — use the FAST test, as this may be a stroke.
- Call 999 for weakness with face drooping, slurred speech, confusion or a severe headache.
- Seek urgent help for weakness that spreads quickly over hours or days, or that begins to affect breathing or swallowing.
- Seek urgent help for weakness with loss of bladder or bowel control, or numbness around the back passage or inner thighs.
- See a doctor promptly for new, unexplained or progressive weakness in a limb, even if it is gradual.
When to see a doctor
Treat sudden weakness, especially down one side of the body or in the face, arm or leg, as an emergency and call 999 — a stroke needs treatment fast. Also seek urgent help if weakness spreads quickly, affects breathing or swallowing, or comes with loss of bladder or bowel control or numbness around the saddle area. For weakness that develops more gradually — difficulty climbing stairs, rising from a chair or lifting the arms — book a prompt appointment so the cause can be investigated, particularly if it is getting worse, is affecting your daily life, or comes with other symptoms such as numbness, pain or weight changes.
Not sure how urgent it is? It is always OK to call NHS 111 for advice, day or night.
What can cause it
Common causes of muscle weakness
Muscle weakness has many possible causes. Each links to a full, plain-language guide to that condition — what it is, how it's treated and when to seek help.
What helps
Self-care and what you can do
New muscle weakness should be assessed rather than managed at home, especially if it is sudden or one-sided. If a clinician has identified a stable, long-standing cause, the focus is on keeping safe and maintaining strength: stay as active as you safely can within the limits you have been given, use any aids or adaptations recommended, and take care to prevent falls by clearing trip hazards and using handrails. Pace your activities and rest when a muscle tires if your weakness fluctuates. Attend follow-up appointments so the cause can be monitored and any treatment reviewed. The single most important thing with new weakness is to recognise the emergency pattern of sudden, one-sided weakness and call 999 without delay.
Answers
Muscle weakness: frequently asked questions
What is the difference between weakness and tiredness?
Weakness is a true loss of muscle power — the muscle cannot do its job. Tiredness or fatigue means the strength is there but everything feels like an effort. Genuine new weakness, especially if sudden or one-sided, needs urgent assessment.
When is muscle weakness an emergency?
Call 999 if weakness is sudden, affects one side of the body or the face, comes with slurred speech or a drooping face, spreads quickly, or affects breathing or swallowing. Sudden one-sided weakness is a classic sign of a stroke.
Can a thyroid or vitamin problem cause weakness?
Yes. An underactive thyroid and a lack of vitamin D can both cause muscle aching and weakness, often gradual and around the hips and thighs. These are found on simple blood tests, so persistent unexplained weakness is worth getting checked.
Why does my weakness get worse later in the day?
Weakness that worsens with use and improves with rest can point to a problem at the junction between nerve and muscle, such as myasthenia gravis, especially if it affects the eyelids, swallowing or breathing. This should be assessed urgently.
Sources
Where this is drawn from
- NICE CKS: Stroke and TIA.
- Brain and Spine Foundation: muscle weakness.
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