What Is Muscle Weakness?

Muscle weakness causes difficulty performing normal muscular contractions, resulting in decreased strength and compromised ability to perform active movements. Muscle weakness can make everyday activities and movements of your arms, legs, and body challenging.

If it is severe, muscle weakness can interfere with your ability to move, sit up, stand, walk, and maintain your balance. Muscle weakness can be caused by an underlying disease, but can also result from other causes, such as aging, recovery from intense exercise or strength training, poor physical conditioning, malnutrition, or taking certain medications.

What Causes Muscle Weakness?

Autoimmune, Neuromuscular, and Neurological Diseases

• Amyotrophic lateral sclerosis (ALS): Also known as Lou Gehrig’s disease, ALS is a disorder that causes damage to the nerves that control muscles and voluntary movement. Symptoms of ALS include muscle weakness, atrophy (wasting), stiffening, spasticity, twitches, and cramping.
• Bell’s palsy: Bell’s palsy is caused by temporary weakness and paralysis of the muscles of the face due to damage or irritation to the facial nerve on one side of the face. This can make it difficult for you to perform motions like raising your eyebrows or opening your mouth. While the exact cause is unknown, Bell’s palsy can result from a viral infection or be exacerbated by stress, but symptoms tend to be temporary and resolve over time.
• Cerebral palsy: Cerebral palsy is a developmental disorder that occurs anytime from before birth through two years of age. It is caused by oxygen deprivation to the developing brain. There are several forms of cerebral palsy, but most cause some form of muscular weakness. Often, children with cerebral palsy have difficulty walking and need crutches or a walker. Children with cerebral palsy also demonstrate an abnormal difference in muscle tone or resting muscle tension, making it difficult for them to actively contract muscles to perform daily movements.
• Cervical spondylosis: Cervical spondylosis, or degenerative changes of the bones of the neck, is an arthritic condition that can cause narrowing of the openings for the cervical nerve roots. Compression of the cervical nerve roots that exit from the spinal cord often occurs in this condition due to the narrowed spaces for the nerves to pass through—this is called cervical stenosis. Nerve root compression can cause pain, tingling, numbness, and weakness in the muscles that are innervated by the nerve roots, such as those of the arms and hands—a condition known as cervical radiculopathy.
• Guillain-Barré syndrome: Guillain-Barré syndrome (GBS) is an autoimmune, neuromuscular disorder that causes progressive loss of nerve function, often starting in the feet and traveling up the legs. The exact cause of Guillain-Barré syndrome is unknown, but it often occurs after an infection or increased period of stress. Symptoms tend to resolve over time, but can take up to a year or more for full recovery. Guillain-Barré syndrome creates widespread muscle weakness, and people often lose their ability to walk temporarily until the condition improves.
• Graves’ disease: Graves’ disease results from an overproduction of thyroid hormones. This can cause muscle weakness, and severe cases of Graves’ disease can cause thyrotoxic hypokalemic periodic paralysis, which causes periods of extreme muscle weakness and paralysis.
• Lambert-Eaton myasthenic syndrome: Lambert-Eaton myasthenic syndrome is an autoimmune disease that affects the neuromuscular junction, the area where a nerve cell communicates with a muscle cell via the release of neurotransmitters (chemical messengers). When the transfer of neurotransmitters is disrupted, muscles do not receive the proper signal that causes them to contract, causing widespread muscle weakness and fatigue.
• Myasthenia gravis: Myasthenia gravis is an autoimmune disease that causes inflammation throughout the body. With myasthenia gravis, the body produces antibodies, immune system proteins that target pathogens, that attack the receptors for the neurotransmitter acetylcholine, reducing the body’s ability to contract muscles. This leads to muscle weakness, atrophy, and fatigue.
• Multiple sclerosis (MS): MS is a neurological condition that causes degeneration of the myelin sheath around nerves, which reduces the impulses sent along these nerves to muscles. This results in muscle weakness, which is often more severe on a person’s dominant side of the body. There are many forms of multiple sclerosis, but the condition is often progressive and gets worse over time. 
• Muscular dystrophies: Muscular dystrophies are a group of genetic diseases characterized by a gradual loss of motor function, muscle weakness and atrophy, difficulty walking, progressive respiratory failure, and cardiomyopathy (disease of the heart muscle).

Electrolyte Imbalances 

Certain electrolyte imbalances can also result in muscle weakness, including:

• Hypercalcemia: Hypercalcemia, or elevated levels of calcium in the blood, alter the electrical charge of muscle cells and electrolyte balance. This can lead to muscle weakness due to the compromised ability of muscle cells to contract properly.
• Hypokalemia: In order for muscles to contract properly, they require adequate levels of the electrolyte potassium, which passes through the cell membrane of nerve and muscle cells. When there is not enough potassium in the blood, called hypokalemia, muscles may not be able to contract properly, leading to muscle weakness.
• Hypomagnesemia: Magnesium deficiency, or hypomagnesemia, can lead to an electrolyte imbalance between magnesium and potassium levels. This can result in fatigue and muscle weakness.

Thyroid Disorders

Conditions that affect the thyroid gland and thyroid hormone production can also lead to muscle weakness, including:

• Addison’s disease: Addison’s disease is an autoimmune disease that causes the body to attack its adrenal glands, which produce hormones to help the body function properly, causing adrenal insufficiency. It prevents the adrenal glands from producing enough of the hormones aldosterone and cortisol. Because these hormones help regulate levels of sodium and potassium in the blood and muscles, insufficient levels can cause impaired ability of muscles to contract, leading to muscle weakness.
• Hypothyroidism: Hypothyroidism, or too little thyroid hormones, can cause muscle weakness. It is believed this occurs due to the high amount of thyroid hormone receptors in muscle cells. Without adequate levels of thyroid hormone, muscles cannot function properly.
• Hyperthyroidism: Myalgia, or muscle pain, and muscle weakness are commonly associated with hyperthyroidism, or too much thyroid hormones. Often, these symptoms occur with treatment to reduce thyroid hormone levels, which results in a rapid decrease in levels and relative hypothyroidism and associated symptoms.

Viruses and Infections

Certain viral infections can result in muscle weakness, including:

• Botulism: Botulism is a rare but serious illness caused by the toxin produced by the Clostridium botulinum bacteria, which are often found in contaminated food. Botulism symptoms usually begin with muscle weakness of the eyes, mouth, throat, and face, causing droopy eyelids, poor vision, slurred speech, and difficulty swallowing. Muscle weakness can progress and spread to the arms, legs, and body, and in severe cases, to the diaphragm, a vital muscle that controls breathing.
• Coronavirus (COVID-19): While research is still ongoing on the long-term effects of COVID-19, persistent fatigue, muscle weakness, and generalized deconditioning have been observed in patients after initial recovery from an infection.
• Epstein-Barr virus infection: Viral infections, including those caused by the Epstein-Barr virus like mono, can cause myositis, or inflammation of muscles, causing muscle weakness, pain, and difficulty walking.
• Human immunodeficiency virus (HIV) infection: HIV attacks and destroys the immune system, and can result in myopathies that damage normal muscle cell structure in function. The most common myopathy caused by HIV is HIV-associated polymyositis, which causes slowly progressing and symmetrical muscle weakness.
• Influenza: The flu virus, or influenza, can cause myositis, or inflammation of muscles, causing muscle weakness, pain, and difficulty walking. Myositis most commonly occurs from an infection like the flu virus.
• Lyme disease: Lyme disease is an infection transmitted by tick bites. It can cause a variety of systemic symptoms like fever, fatigue, pain, vision changes, memory problems, and generalized muscle weakness.
• Meningitis: Meningitis causes inflammation of the meninges, the membranes that surround the brain and spinal cord, and can be caused by a bacteria, virus, fungus, or parasite. Meningitis can progress to cause loss of sensation, memory loss, muscle weakness, paralysis, and seizures.
• Rabies: Rabies is caused by the rabies virus that is transmitted through a bite from an animal infected with the virus. Symptoms of rabies include flu-like symptoms, fever, and generalized muscle weakness.
• Rheumatic fever: Rheumatic fever develops after an infection from strep throat, causing fever, painful and swollen joints, fatigue, muscle weakness, and heart problems.
• Syphilis: Syphilis is a sexually transmitted infection that causes a bacterial infection. Untreated syphilis can cause syphilitic myelopathy, which develops from damage to the spinal cord and nerves, causing abnormal sensations, muscle weakness, and impaired coordination.
• Toxoplasmosis: Toxoplasmosis is a parasitic infection acquired through food contaminated by the parasite toxoplasma gondii. While healthy people typically do not suffer serious illness, people with compromised immune systems, especially those with AIDS or pregnant women, can experience serious health problems from toxoplasmosis. It may cause flu-like symptoms, eye problems, and chronic muscle inflammation and weakness.
• West Nile virus infection: West Nile virus is a virus transmitted by mosquitoes. While most people only experience minor symptoms, less than 1% of people who contract West Nile virus develop serious symptoms, including neurological damage, such as arm or leg paralysis, skeletal muscle inflammation, peripheral nerve damage, generalized muscle weakness, and fatigue.

Secondary to Other Issues

Muscle weakness can also develop due to other issues, such as:

• Alcoholism: Chronic consumption of excessive alcohol can cause alcoholic myopathy, or muscle dysfunction due to increased levels of inflammation and oxidative stress. Symptoms of alcoholic myopathy include muscle pain, wasting, weakness, and swelling.
• Anemia: Muscles require adequate levels of iron to function properly due to their high energy demand. With anemia, levels of red blood cells that carry iron are significantly reduced, leading to muscle dysfunction and weakness.
• Cancer: Cancer and cancer treatment can cause cachexia, muscle wasting, and weakness as a result of destruction of motor units of muscle cells that affect muscle structure and function.
• Chronic fatigue syndrome: Chronic fatigue syndrome is a disorder of unknown cause, but may be triggered by an infection, immune system change, or stress, resulting in extreme fatigue, muscle weakness, and muscle and joint pain.
• Diabetes: Patients with diabetes can develop complications like diabetic amyotrophy, leading to muscle wasting and weakness, along with extreme pain in the thighs, hips, and buttocks.
• Fibromyalgia: Fibromyalgia causes widespread pain throughout the body. Common symptoms include pain, fatigue, and tingling and weakness in the arms and legs.
• Herniated disc: It is common for herniated discs to compress the nerve roots that exit from the spinal cord. Nerve compression can prevent the signaling from the nerves to the muscles from being delivered properly, resulting in muscle weakness, numbness, tingling, and pain. 
• Hypotonia: Hypotonia, or a lack of muscle tone, which is the amount of resting tension in a muscle, causes muscles to become flaccid and weak. 
• Insomnia: Insomnia is a sleeping disorder that makes it very difficult to fall asleep at night. Lack of restful sleep interferes with the body’s ability to remove toxins from the body and reduce inflammation, which can result in chronic fatigue and muscle weakness.
• Kidney disease: Chronic kidney disease causes muscle protein degradation due to altered insulin signaling pathways. This results in muscle wasting and weakness.
• Narcolepsy: Narcolepsy is a sleeping disorder that causes excessive sleepiness during the day. Lack of restful sleep can cause generalized fatigue and muscle weakness, and narcolepsy can also cause brief periods of exaggerated muscle weakness, called cataplexy.
• Neuralgia: Nerve pain, or neuralgia, results from damaged or irritated nerves. While neuralgia can occur anywhere in the body, it is common in the face—this type is called trigeminal neuralgia. Along with pain, neuralgia can cause burning, tingling, and numbness.
• Nerve or spinal cord injury: Injury to nerves or the spinal cord can significantly impact the signals that travel from nerves to muscles, reducing the ability of these muscles to contract and leading to muscle weakness.
• Peripheral neuropathy: Peripheral neuropathy refers to conditions that damage the nerves of the peripheral nervous system, which controls sensation and movement of parts of the body outside the brain and spinal cord. Nerve damage from peripheral neuropathy can cause pain, numbness, tingling, burning, and muscle weakness.
• Poisoning: Poisoning can damage and destroy nerve cells, reducing the signals sent to muscles to contract, which causes muscle weakness. 
• Polymyositis: Polymyositis is an inflammatory, autoimmune condition that develops over time and causes muscle weakness, which can make it difficult to perform everyday movements.
• Prolonged immobilization or bed rest: A sedentary lifestyle and prolonged lack of movement from bed rest or immobilization—such as from wearing a cast after an injury—causes muscle weakness and atrophy from lack of use and stimulation.
• Stroke: A stroke, or cerebral vascular accident, can cause damage to the part of your brain that controls sensation and movement. Often, a stroke will produce hemiplegia, or weakness on one side of the body. 

Secondary to Long-Term Use of Some Drugs

Muscle weakness can be a side effect of taking certain types of medications. These include:

• Amiodarone, used to treat irregular heart rhythms
• Antiarrhythmic drugs, used to treat heart rhythm abnormalities
• Antithyroid medications, used to treat hyperthyroidism
• Antiretroviral medication, used to treat HIV
• Chemotherapy medications, used to treat cancers
• Cimetidine, used to treat stomach ulcers
• Colchicine, used to treat gout attacks
• Corticosteroids, used to decrease inflammation throughout the body for many inflammatory conditions
• Illicit drugs, such as heroin and cocaine
• Interferon, used to treat viral infections and cancer
• Leuprolide acetate, used to treat prostate cancer
• NSAIDs, or nonsteroidal anti-inflammatory drugs, like Advil (ibuprofen) and Tylenol (acetaminophen), used to treat pain and inflammation 
• Penicillin, used to treat bacterial infections
• Statins, used to treat high cholesterol
• Sulfonamide drugs, used as antibiotics

Rare Causes of Muscle Weakness

Certain rare conditions can cause muscle weakness:

• Dermatomyositis: Dermatomyositis is an inflammatory myopathy, or muscle disorder, that also causes skin irritation and rash. Due to the inflammation that develops with dermatomyositis, muscle tissue can break down, causing pain and weakness.
• Rheumatoid arthritis (RA): RA is an inflammatory, autoimmune form of arthritis that causes progressive joint inflammation and damage, leaving joints painful and stiff and causing muscle weakness around affected joints.
• Sarcoidosis: Sarcoidosis is a systemic, inflammatory condition of unknown cause with symptoms like arthritis, joint pain, and sarcoid myopathy, which is characterized by muscle weakness, pain, and fatigue.
• Secondary hyperparathyroidism: Secondary hyperparathyroidism, or excessive parathyroid hormones, is a common complication of kidney disease. Secondary hyperparathyroidism can cause joint pain and muscle weakness as increased parathyroid hormone levels contribute to muscle protein breakdown.
• Systemic lupus erythematosus (SLE): SLE is a systemic, autoimmune condition that causes a skin rash and joint inflammation. It also causes myalgia (muscle pain) and myositis (muscle inflammation), leading to muscle weakness.

Diagnosis and Treatment for Muscle Weakness

Your doctor will ask you questions about your medical history, medications you are taking, and any unusual symptoms you are experiencing.

Diagnostic tests that may be ordered to help determine a diagnosis include:

• Bloodwork to assess levels of enzymes, electrolytes, hormones, and inflammatory markers
• Genetic testing to assess for genetic risk
• Magnetic resonance imaging (MRI) of your brain, spinal cord, and nerves to assess for damage
• Electromyography (EMG) to assess the electrical activity of your muscles
• Nerve conduction tests to assess how signals travel from your nerves to your muscles
• Muscle biopsies to examine the quality of your muscle tissue
• Lumbar puncture, also called a spinal tap, to assess the quality of your cerebrospinal fluid within your spinal canal

Only a licensed healthcare provider can determine proper treatment depending on the cause of your muscle weakness. Treatment options include medication, dietary changes, physical and occupational therapy, and in certain cases, surgery.

Physical Therapy

Physical therapy sessions with a licensed physical therapist can help strengthen weak muscles, restore muscle imbalances, and improve your mobility and ability to complete daily activities that might become challenging due to muscle weakness, such as standing up from a chair, walking, and going up and down stairs.

Patients with autoimmune, neuromuscular, and neurological diseases can benefit most from physical therapy, as well as people who suffer from muscle weakness due to a sedentary lifestyle, immobilization, or lack of activity.

Occupational Therapy

Occupational therapy is similar to physical therapy, but focuses more on strengthening the muscles of the hands, wrists, and upper body to improve coordination, fine motor movements, dexterity, and activities of daily living. Occupational therapy can help you regain the strength in your hands and arms to be able to function day to day with fewer limitations.

Medication

Medication may be prescribed to help treat the underlying cause of your muscle weakness. Pain-relieving and anti-inflammatory medications can help alleviate nerve irritation, which can lead to muscle weakness, while thyroid medications can be used to manage thyroid disorders.

Steroids and biologics are also often prescribed to decrease inflammation in autoimmune conditions that can cause muscle weakness. If an infection is present, antibacterial, antiviral, or antifungal medications will be prescribed to help your body recover.

Dietary Changes

Improving your diet and taking supplements can help improve electrolyte imbalances and nutritional deficiencies that can cause muscle weakness. Depending on your doctor’s recommendations, you may have to increase your intake of iron, magnesium, or potassium.

Surgical Intervention

Surgery may be needed for muscle weakness caused by herniated discs or other forms of nerve injuries or compression. It is usually considered when other forms of treatment fail to improve symptoms.

Surgery will involve removing tissue that is causing nerve compression. If hyperthyroidism is unresponsive to other treatment, surgery may also be performed to remove some or all of the thyroid gland.

Summary 

There are many potential causes of muscle weakness, but all are signs that something abnormal is going on. Make sure to discuss your symptoms and history of muscle weakness with your doctor, and seek immediate medical attention for any sudden, unexplained weakness in your muscles.