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Muscle weakness
Category: Brain & Nerves · All brain & nerves symptoms
What it can feel like
Muscle weakness means a real loss of power — difficulty rising from a chair, climbing stairs, lifting the arms to wash hair, a foot that drags — as opposed to feeling tired or achy. Patterns matter: one limb, both legs, face involved, sudden or gradual, with or without wasting or twitching.
Possible causes
A symptom can have many causes, and most are not serious. The lists below group conditions this symptom can be associated with — common causes first. They are possibilities to discuss with a clinician, not a diagnosis.
Common causes
Weakness can be associated with deconditioning after illness or inactivity, with pain limiting effort, electrolyte disturbances, an underactive thyroid, and medicines such as steroids used long-term.
Other possible causes
Weakness can also be associated with stroke (sudden, one-sided), nerve root or peripheral nerve damage, inflammatory muscle disease, motor neurone disease (painless, progressive, with twitching and no numbness), and disorders of the nerve–muscle junction such as myasthenia gravis (fatigable weakness).
Red flags — when to seek help promptly
- Sudden weakness of the face, arm or leg — emergency (possible stroke)
- Weakness that is ascending up the legs over days, especially after an infection — urgent
- Weakness with difficulty breathing, swallowing or speaking
- Weakness with loss of bladder or bowel control or saddle numbness
- Progressive painless weakness with muscle twitching
What a clinician may do
A clinician will grade strength in each muscle group, look for wasting and twitching, test reflexes and sensation, and watch walking and rising from a chair. Blood tests, nerve conduction studies with muscle electrical testing (EMG), and imaging of brain or spine follow the pattern. Time-critical patterns are triaged as emergencies.
Watch: related videos
Examination and clinical videos from the MedicalVideos.com library relevant to this symptom. Some clinical footage is graphic — that is the nature of a medical video library.
Related guides on MedicalVideos.com
Frequently asked questions
Why does it matter that my weakness doesn't hurt?
Pain usually means the problem is in muscles, joints or inflamed tissue. Painless, progressive weakness with wasting and twitching points instead to the motor nerves themselves and changes the investigation entirely — it is a pattern clinicians treat as a priority, not a reassurance.
Weakness versus fatigue — how do doctors tell?
By testing: fatigue means the power is there when formally tested but endurance and drive are low; weakness means maximum force itself is reduced on examination. Bring examples — stairs, jars, rising from low chairs — because your functional history is the most sensitive early measure.
Related symptoms — Brain & Nerves
Browse the M section of the A–Z list or return to the Symptoms A–Z hub.