Leg Weakness: Causes and When to Worry

What leg weakness feels like

Leg weakness can be subtle at first. People notice:

• difficulty climbing stairs or standing up from a low chair without using their arms
• knees that buckle or give way
• the toes catching on the ground, or a foot that slaps down
• tripping or falling more often
• legs that feel heavy, like walking through mud

Fatigue, joint pain and poor balance can feel similar. True weakness means the muscles cannot produce normal force. A doctor will test this directly.

Medical terms for leg weakness

Sudden leg weakness: emergency causes

• Stroke: sudden weakness of one leg, usually with the arm and face on the same side. Weakness of one leg alone happens with strokes in the front part of the brain.
• Spinal cord compression: from a disc, tumor, abscess, bleed or fracture. Weakness in both legs, a numb band across the trunk, and bladder problems.
• Cauda equina syndrome: compression of the nerve roots at the bottom of the spine. Back pain, sciatica in one or both legs, saddle numbness and bladder or bowel changes. Needs surgery within hours.
• Guillain-Barré syndrome: the immune system attacks the nerves, usually 1 to 4 weeks after a gut or chest infection. Tingling and weakness start in the feet and climb over days. It can paralyze breathing muscles.
• Transverse myelitis: inflammation of the spinal cord causing weakness, numbness and bladder problems over hours to days.
• Low or high potassium: severe hypokalemia from diuretics, vomiting or diarrhea causes generalized weakness, often legs first.

Gradual leg weakness: nerve causes

• Sciatica and herniated disc: a disc pressing on a nerve root in the lower back causes pain shooting down one leg, with weakness in a specific pattern. An L5 root problem causes foot drop.
• Lumbar spinal stenosis: narrowing of the spinal canal in older adults. Legs feel weak, heavy and achy after walking a distance and recover after sitting or leaning forward on a shopping cart.
• Peripheral neuropathy: diabetes, alcohol, B12 deficiency and chemotherapy damage the longest nerves first, causing numb, burning feet and weak ankles.
• Peroneal nerve palsy: pressure at the outside of the knee from crossing the legs, weight loss or a cast causes foot drop.
• Multiple sclerosis: stiff, weak legs that worsen with heat, often with vision or bladder symptoms.
• ALS (motor neuron disease): painless, progressive weakness with muscle twitching and wasting, often starting in one leg.

Gradual leg weakness: muscle and other causes

• Sarcopenia and deconditioning: muscle loss with age, illness, bed rest or inactivity. Thighs weaken first.
• Medicines: statins (with muscle aches), long-term steroids, and some HIV and cancer drugs.
• Thyroid disease: both overactive and underactive thyroid cause thigh weakness.
• Inflammatory muscle disease (polymyositis, dermatomyositis): thigh and shoulder weakness, sometimes with a rash.
• Muscular dystrophies: inherited, usually starting in childhood or early adulthood.
• Peripheral artery disease: leg cramping and weakness on walking that eases with rest, with cold feet and weak pulses.
• Low vitamin D, anemia, heart failure and depression can make legs feel weak and tired.

One leg vs both legs

How doctors diagnose the cause

A doctor will ask how quickly the weakness started, whether one or both legs are affected, about pain, numbness, bladder and bowel function, recent infections, medicines, alcohol and diabetes. The examination tests strength in each muscle group, reflexes, sensation, walking, and the ability to rise from a squat.

Tests depend on the clues:

• MRI of the spine for compression and stenosis, or of the brain for stroke and MS
• blood tests: potassium, glucose, B12, thyroid function, creatine kinase (a marker of muscle damage), kidney function
• nerve conduction studies and EMG for neuropathy and muscle disease
• lumbar puncture for Guillain-Barré and some inflammatory conditions

Treatment

Treatment targets the cause:

• emergency clot-busting or clot-removal treatment for stroke
• urgent surgery for cauda equina or cord compression
• immune treatments (IV immunoglobulin or plasma exchange) for Guillain-Barré
• physical therapy, pain relief and sometimes surgery for sciatica and stenosis
• blood sugar control and vitamin replacement for neuropathy
• stopping or changing a responsible medicine
• an ankle-foot orthosis (brace) for foot drop

Strengthening and safety at home

For age-related or inactivity-related weakness, progressive strength training is the most effective treatment. Sit-to-stand exercises, step-ups, heel raises and leg presses 2 to 3 times a week build strength at any age. Remove trip hazards, add stair rails and use a cane or walker if a therapist recommends one.

Frequently asked questions

What are the symptoms of leg muscle weakness?

Common symptoms are trouble climbing stairs or rising from a chair, knees that buckle, tripping, foot drop, heavy legs and falls. Weak thighs suggest a muscle cause, while weak feet and ankles with numbness suggest a nerve cause.

What neurological problems cause leg weakness?

Stroke, spinal cord compression, cauda equina syndrome, pinched lower-back nerves, spinal stenosis, peripheral neuropathy, multiple sclerosis, Guillain-Barré syndrome and ALS all cause leg weakness. The pattern of weakness and numbness helps locate the problem.

What is the medical term for left leg weakness?

Weakness of one leg is called monoparesis, and complete paralysis of one leg is monoplegia. If the left arm is also weak, it is called left hemiparesis, which is typical of a stroke affecting the right side of the brain.

When is sudden leg weakness an emergency?

Always treat sudden leg weakness as an emergency, especially with facial droop, speech problems, numbness in the saddle area, bladder or bowel changes, severe back pain or weakness that is spreading upward. Call 911 or your local emergency number.

Can anxiety make your legs feel weak?

Yes. Anxiety and panic can make legs feel shaky, jelly-like or heavy because of adrenaline and muscle tension. The strength is normal on testing and it passes when the anxiety settles. New or persistent weakness should still be checked by a doctor.