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What causes muscle weakness? 41 possible conditions

What Is Muscle Weakness?

Feeling weak is not all that uncommon. Whether you are ill or simply need rest, muscle weakness happens to nearly everyone at some point in their life. 

The definition of true muscle weakness, however, is when your full effort does not produce a normal muscle contraction or movement. You may hear it also referred to as reduced muscle strength, muscular weakness, or weak muscles. 

A voluntary muscle contraction is usually generated when the brain sends a signal through the spinal cord and nerves to a muscle. If the brain, the nervous system, the muscles, or the connections between are injured or affected by disease, the muscle won’t contract normally and muscle weakness is the resultant symptom.

This is different from the weakness you may feel as a result of a tough workout, for instance. The difference is that a workout will exhaust muscles and there is recovery with rest, but true muscular weakness is a sign of something deeper.

Potential Causes of Muscle Weakness

There are many possible underlying causes for muscle weakness. Possible causes include:

  • chronic fatigue syndrome
  • muscular dystrophy
  • Graves disease
  • Guillain-Barré syndrome
  • hypothyroidism
  • hypotonia (lack of muscle tone, usually present at birth)
  • Lou Gehrig’s disease
  • myasthenia gravis (an autoimmune and muscular disorder)
  • neuralgias (sharp burning or pain in one or more nerve)
  • peripheral neuropathy (nerve damage)
  • polio
  • rheumatic fever
  • West Nile virus
  • hypercalcemia (elevated calcium in the blood)
  • botulism (a rare and serious illness caused by the bacterium Clostridium botulinum)
  • polymyositis (chronic muscle inflammation)
  • stroke
  • prolonged bed rest or immobilization

Diagnosing the Underlying Cause of Muscle Weakness

When you experience muscle weakness and there is no normal, logical explanation for it, make an appointment to see your doctor. Your doctor will ask you questions about the weakness, how long you have had it, and what muscles are affected. The evaluation will also determine if muscle atrophy is present.

Your doctor will also check your reflexes, sensation, and muscle tone. If further investigation is needed, the doctor may order tests including:

  • CT scan
  • MRI
  • nerve tests
  • electromyography (tests nerve activity in the muscles)
  • blood tests

Treatment Options for Muscle Weakness

Once the cause of your muscle weakness is determined, your doctor can decide on proper treatment. The treatment will depend on the underlying problem and the severity of the symptoms. In some cases, physical therapy may be helpful. In others, medication may be the best option for relief.

Recognizing a Potential Emergency Situation

In some cases, muscle weakness can be a sign of something very serious like a stroke. If you experience any of the following symptoms, call 911 immediately.

  • Any sudden onset of muscle weakness, such as being unable to move an arm or leg, or problems walking, standing, or sitting upright.
  • Any sudden onset of being unable to smile or make facial grimaces.
  • Any chest muscle weakness resulting in difficulties breathing.

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See a list of possible causes in order from the most common to the least.


CFS (Chronic Fatigue Syndrome)

Chronic fatigue syndrome (CFS) is a debilitating disorder characterized by extreme tiredness that can't be explained by an underlying medical condition.

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Muscular Dystrophies

Muscular dystrophies are a group of inherited diseases that damage and weaken your muscles over time. This damage and weakness is due to the lack of a protein.

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Dermatomyositis is a rare inflammatory disease. It's an inflammatory myopathy, which is a condition that occurs when your muscles become inflamed.

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Poliomyelitis, or polio, is a highly contagious disease that is caused by a virus that attacks the body's nervous system. It is most likely to be contracted by children under five years old.

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Low Blood Sodium (Hyponatremia)

Low blood sodium, or hyponatremia, occurs when water and sodium are out of balance in your body. A quick drop in sodium levels can cause weakness, headache, nausea, and muscle cramps.

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Osteomalacia is a weakening of the bones due to problems with bone formation or the bone building process. It is not the same as osteoporosis, which is a weakening of living bone that has already been formed and i...

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This condition is considered a medical emergency. Urgent care may be required.

A concussion is a mild traumatic brain injury. Usually it occurs after an impact to your head or after a whiplash-type injury. A concussion can cause many severe symptoms that affect brain function.

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Low Blood Potassium

Hypokalemia occurs when the blood's potassium levels are too low. A normal level of potassium is 3.6-5.2 millimoles per liter. Levels below 3.6 are considered low.

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Myasthenia Gravis

Myasthenia gravis is a neuromusclar disorder. It results in weakness of the skeletal muscles, and can cause double vision and drooping of the eyelid.

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Neuralgia is a stabbing, burning, and often quite severe pain that occurs along a damaged nerve. It has several causes, from shingles to diabetes or multiple sclerosis.

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Stroke Overview

This condition is considered a medical emergency. Urgent care may be required.

A stroke (a "brain attack") is a medical emergency in which part of the brain is deprived of oxygen. This occurs when an artery that supplies oxygenated blood to the brain becomes damaged and brain cells begin to die.

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Slipped (Herniated) Disk

The vertebrae in your spine are cushioned by disks composed of a hard outer ring with a gelatinous material inside. Injury or weakness can cause the inner portion of the disk to break through the outer portion.

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Graves' Disease

Graves disease is an autoimmune disorder that leads to hyperthyroidism and causes thyroid swelling.

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Rickets is a nutritional disorder that can develop if you do not get enough vitamin D, calcium, or phosphate. Rickets leads to poor functioning of a bone's growth plate (growing edge), softened and weakened bones...

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Peripheral Neuropathy

Peripheral neuropathy occurs when nerves malfunction because they're damaged or destroyed. You'll notice a tingling, numbness, or weakness, and possibly sweating, constipation, or diarrhea.

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Hypercalcemia is a condition in which you have too much calcium in your blood. Serious cases could cause symptoms like abdominal pain, nausea, constipation, and weakness.

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The thyroid gland produces a hormone that controls how your cells use energy (metabolize). Hypothyroidism occurs when the body doesn't produce enough. Untreated, it can cause complications like obesity and heart disease.

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Duchenne Muscular Dystrophy

One of the nine types of muscular dystrophy, Duchenne muscular dystrophy (DMD) is a genetic condition characterized by progressive weakening of voluntary muscles that leads to death. DMD worsens more rapidly than othe...

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Mini Stroke (Transient Ischemic Attack)

This condition is considered a medical emergency. Urgent care may be required.

During a transient ischemic attack (TIA, mini stroke) blood stops flowing to the brain for a short period of time. TIA doesn't kill brain cells like a stroke does. TIA causes symptoms that mimic those of a stroke.

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ALS (Lou Gehrig's Disease)

Amyotrophic Lateral Sclerosis (ALS) is not contagious. It is a degenerative disease that affects the brain and spinal cord. A chronic disorder, it causes a loss of control of voluntary muscles. The nerves controllin...

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This feature is for informational purposes only and should not be used to diagnose.
Please consult a healthcare professional if you have health concerns.