Upper Arm Weakness: Causes & Treatment

Upper left or right arm weakness can be caused by nerve damage or compression of the shoulder, repetitive strain injury of the shoulder, or a pinched nerve in the neck. Read below for more information on upper arm pain and weakness and when you should seek medical attention.

Weakness in one upper arm symptoms

Experiencing weakness in one upper arm, whether it happens suddenly or over time, can be quite worrisome. Acute weakness in one upper arm can be a sign of a medical emergency such as a stroke. Chronic upper arm weakness should also be examined.

Common accompanying symptoms of weakness in one upper arm

Associated symptoms you may experience with weakness in one upper arm may include:

  • Pain
  • Difficulty lifting the arms
  • Difficulty performing daily tasks: Brushing teeth, combing the hair, grasping objects, etc.
  • Numbness or tingling
  • Limited range of motion

What is true weakness?

When discussing weakness, it is important to differentiate between true weakness and weakness related to other conditions. True weakness is defined as a decrease in muscle power and is not related to pain, joint dysfunction, or generalized fatigue that may occur after a strenuous workout or from trying a new sport.

Diagnosing true weakness requires an exam with your physician. Make an appointment if you experience any of the symptoms above for a proper diagnosis.

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Causes of weakness in one upper arm

Muscle strength is determined by a complex interplay of nerves, muscle protein, and ions that allow muscle fibers to contract and create force. Any process that disrupts this system can result in weakness of the upper arm.

Neurologic causes

Damage or disruption to the nerves that supply the muscles can result in weakness because nerves provide the stimulation for muscles to contract. Without nervous system stimulation, the muscles do not contract and will waste away and atrophy.

  • Central: The central nervous system (CNS) consists of the brain and spinal cord. The central nervous system is the primary control center for all of the tasks we perform on a daily basis. Decreased blood flow to the central nervous system (either from blockage or hemorrhage) can result in death or permanent neurological deficits such as hemiplegia, numbness, balance problems, and many more depending on the area affected. In weakness in one upper arm, the blood vessel in the brain most commonly affected is the middle cerebral artery. Other conditions that cause bleeding within the skull (hematomas) can also result in symptoms of weakness.
  • Peripheral: The upper arm is controlled by a complicated branching system of nerves called the brachial plexus. This plexus of nerves start from the cervical spinal cord, travels down the neck, over the first rib, and into the armpit to provide innervation to not only the arm and hand but also the chest and shoulder. See an image of the brachial plexus here and here. Damage to these nerves from a variety of causes (inflammatory, compressive, hereditary) can result in true muscle weakness.

Muscular causes

A variety of conditions can damage or injure muscles or muscle fibers and result in weakness.

  • Hereditary: There are genetic conditions that cause progressive weakness and loss of muscle mass. For example, muscular dystrophy is a group of muscle diseases in which gene mutations interfere with the proper production of proteins necessary for making healthy muscles.
  • Inflammatory: Inflammatory myopathies are a group of diseases that involve chronic muscle inflammation. Myopathy is a general medical term used to describe a number of conditions affecting the muscles. All myopathies cause muscle weakness and sometimes pain. These inflammatory myopathies can occur in autoimmune disorders where the immune system attacks itself, and also from infectious causes such as bacteria, viruses, and fungi.
  • Drugs and toxins: There are many medications that can cause muscle weakness. From steroids to cholesterol medications, it is important to inform your healthcare provider of any drugs you are taking. They can also assist you in finding support if you are struggling with a usage problem.

Systemic causes

People with a variety of systemic disorders may mistake limitations as weaknesses. This type of weakness is better described as fatigue and is not considered true weakness. Possible conditions that may result in this type of weakness include cardiopulmonary disease, joint disease, anemia, malignancy, chronic infectious or inflammatory disease, and/or depression. However, the lack of use of certain muscles from these conditions may progress to true muscle weakness.

This list does not constitute medical advice and may not accurately represent what you have.

Brachial plexopathy (shoulder nerve issue)

The brachial plexus is a web of nerves between the neck and shoulder, connecting the spinal cord nerves to the arm. There is one web on each side of the neck. Any injury that forces the shoulder to stretch down, and the neck to stretch up and away, can damage these nerves and cause brachial plexopathy.

Sports injuries and car accidents are often involved. Inflammation, tumors, and radiation treatment can also damage the brachial plexus.

Milder symptoms include numbness and weakness in the arm, with a shocklike stinging or burning sensation. A more severe injury can cause paralysis and loss of feeling in the arm, with pain in some parts of the arm, hand, and shoulder.

These symptoms should be seen by a medical provider since permanent damage can result if the injuries are not treated.

Diagnosis is made through electromyography (EMG) testing, CT scan, MRI, and sometimes angiogram.

Treatment usually involves rest and physical therapy. Surgery may be necessary to remove scar tissue or repair the damaged nerves.

Rarity: Uncommon

Top Symptoms: pain in one arm, shoulder pain that shoots to the arm, arm weakness, numbness in one arm, shoulder pain

Symptoms that never occur with brachial plexopathy (shoulder nerve issue): pain in the front middle part of the neck

Urgency: Primary care doctor

Repetitive strain injury of the upper arm

Repetitive strain injury of the upper arm is caused by consistent repetitive use.

Rarity: Uncommon

Top Symptoms: upper arm pain from overuse, upper arm weakness, upper arm numbness

Symptoms that always occur with repetitive strain injury of the upper arm: upper arm pain from overuse

Symptoms that never occur with repetitive strain injury of the upper arm: upper arm injury, severe upper arm pain

Urgency: Self-treatment


Rhabdomyolysis is a syndrome most commonly resulting from muscle injury following extreme exertion such as endurance exercise or weight lifting or following a severe accident. Sometimes rhabdomyolysis may result from medications - most commonly medications to treat elevated cholesterol such as statins. Severity can range from mild to life threatening kidney disease from muscle enzymes entering the circulation.

Rarity: Rare

Top Symptoms: fatigue, nausea, muscle aches, being severely ill, change in urine color

Urgency: Emergency medical service

Stroke or tia (transient ischemic attack)

Transient ischemic attack, or TIA, is sometimes called a "mini stroke" or a "warning stroke." Any stroke means that blood flow somewhere in the brain has been blocked by a clot.

Risk factors include smoking, obesity, and cardiovascular disease, though anyone can experience a TIA.

Symptoms are "transient," meaning they come and go within minutes because the clot dissolves or moves on its own. Stroke symptoms include weakness, numbness, and paralysis on one side of the face and/or body; slurred speech; abnormal vision; and sudden, severe headache.

A TIA does not cause permanent damage because it is over quickly. However, the patient must get treatment because a TIA is a warning that a more damaging stroke is likely to occur. Take the patient to the emergency room or call 9-1-1.

Diagnosis is made through patient history; physical examination; CT scan or MRI; and electrocardiogram.

Treatment includes anticoagulant medication to prevent further clots. Surgery to clear some of the arteries may also be recommended.

Rarity: Common

Top Symptoms: dizziness, leg numbness, arm numbness, new headache, stiff neck

Symptoms that never occur with stroke or tia (transient ischemic attack): bilateral weakness

Urgency: Emergency medical service

Amyotrophic lateral sclerosis (als)

Amyotrophic lateral sclerosis is also called ALS or Lou Gehrig's Disease named after the Hall of Fame baseball player whose career ended when he developed ALS. It is a degenerative disease that destroys nerve cells, which eventually ..

Pinched nerve in the neck

A pinched nerve in the neck is also called cervical radiculopathy. It means that a nerve in the neck, at a point where it branches off from the spinal cord, is being compressed by the surrounding bones, muscles, or other tissues.

It can be caused by a traumatic injury, such as from sports or an automobile accident, especially if the injury results in a herniated disk. It may also arise from the normal wear and tear of aging.

Symptoms include sharp, burning pain with numbness and tingling from the neck to the shoulder, as well as weakness and numbness into the arm and hand.

Diagnosis is made through patient history, physical examination, and simple neurological tests to check the reflexes. Imaging such as x-ray, CT scan, or MRI may be done, as well as electromyography to measure nerve impulses in the muscles.

A pinched nerve in the neck often improves with simply a few days or weeks of rest. Physical therapy, nonsteroidal anti-inflammatory drugs, and steroid injections into the spine can all be very helpful.

Rarity: Common

Top Symptoms: pain in one shoulder, spontaneous shoulder pain, pain that radiates down arm, pain in the back of the neck, severe shoulder pain

Urgency: Primary care doctor

Rotator cuff tendinitis

The rotator cuff is an arrangement of muscles and tendons that holds the head of the upper arm bone within the shoulder socket. Rotator cuff tendinitis is the resulting condition when these muscles and tendons become inflamed or damaged.

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Weakness in one upper arm treatments and relief

Treatment for weakness in the upper arm is largely focused on physical rehabilitation and therapy. Some causes of upper arm weakness discussed above may require specific treatments, such as antibiotics for certain infections or steroids for inflammation. However, once the upper arm weakness results, treatment must be based on physical therapy in order to restore strength, function, and mobility to the arm.

FAQs about weakness in one upper arm

Will I ever be able to use my arm?

Often, in the setting of neurologic causes of weakness or systemic causes of fatigue, dedicated physical therapy (PT) and rehabilitation can help restore some function in the arm. Unfortunately, for some muscular etiologies of upper arm weakness (especially hereditary or autoimmune causes) muscle function can continue to decline despite physical therapy. It is important to realize that many factors may contribute to how well your arm function is restored, such as age and disease severity.

What are the signs of a stroke?

The mnemonic FAST is a good way to remember the signs of stroke and what to do next. Facial droop, arm weakness, and speech difficulty are all signs that it is time to call an emergency responder. Strokes require prompt attention in order to achieve the best outcomes.

How can I identify true muscle weakness?

True muscle weakness is defined as a decrease in muscle power and identified by formal muscle testing. An examiner assesses the strength of each muscle by determining how much force is needed to overcome maximal contraction. A grading system from zero to five is often used and documented as the following:

  • Zero: No muscle contraction
  • One: A flicker or trace of muscle contraction
  • Two: Limb or joint movement is possible only with gravity eliminated
  • Three: Limb or joint movement against gravity only
  • Four: Power decreased but limb or joint movement is possible against resistance
  • Five: Normal power against resistance

Will my upper arm weakness affect my daily activities?

True upper arm weakness can have a profound effect on activities of daily living. Individuals with true muscle weakness often experience complete paralysis and inability to use the affected limb. For individuals with some residual function, completing daily activities such as combing the hair, brushing the teeth, writing, grasping objects, etc. can be extremely difficult without the help of physical therapy.

What kind of exercises will help with my upper arm weakness?

Your physician will most likely suggest formalized sessions with a physical therapist in order to help regain strength, function, and mobility of the upper arm. Exercises and strategies you may encounter include:

  • Practicing everyday tasks repetitively
  • Rehearsing: Imagining doing activities without actually doing them.
  • Constraint-induced movement therapy: This technique involves covering/occluding the unaffected arm to encourage the use of the affected limb.
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Questions your doctor may ask about weakness in one upper arm

  • Do you have any idea what may have caused your upper arm pain?
  • Have you ever been diagnosed with diabetes?
  • Did you just suffer from a high impact injury (e.g., a fall, collision, accident or sports trauma)?
  • Have you been experiencing dizziness?

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  2. Saguil, A. Evaluation of the Patient with Muscle Weakness. Am Fam Physician. 2005 Apr 1;71(7):1327-1336. AAFP Link
  3. Inflammatory Myopathies Fact Sheet. National Institute of Neurological Disorders and Stroke. Updated July 6, 2018. NINDS Link
  4. Warning signs of stroke. American Stroke Association. Stroke Association Link
  5. Levin, MC. Weakness. Merck Manual Professional Version. Updated July 2016. Merck Manuals Link
  6. Upper limb management after stroke fact sheet. Stroke Foundation. Stroke Foundation Link