Read below about weakness in one upper arm, including causes, treatment options and remedies. Or get a personalized analysis of your weakness in one upper arm from our A.I. health assistant. At Buoy, we build tools that help you know what’s wrong right now and how to get the right care.

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Weakness in One Upper Arm Symptoms

Symptoms of weakness in one upper arm, whether it happens suddenly or gradually over time, can be quite worrisome. Often, acute weakness in one upper arm can be a sign of a medical emergency such as a stroke, but chronic upper arm weakness is also a concerning medical finding that requires appropriate follow-up.


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

When discussing weakness, it is important to differentiate between true weakness and weakness that is secondary to other conditions. True weakness is defined as a decrease in muscle power — a condition in which the force exerted by the muscles for any given activity is less than expected. True weakness is not weakness or difficulty moving or using the upper arm due to pain or joint dysfunction or generalized fatigue, such as after a strenuous workout or from trying a new sport [1].

Diagnosing true weakness requires discussion and a physical examination with your physician. Make an appointment promptly if you experience any of the symptoms above in order to properly identify the cause of your symptoms.

Weakness in One Upper Arm Causes Overview

Muscle strength is dictated 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 true weakness of the upper arm.


Damage or disruption to the nerves that supply the muscles can result in true weakness because nerves provide the stimulation that allows muscles to contract. Without nervous system stimulation, the muscles do not contract and will waste away and atrophy [5].

  • 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 (whether via 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 starts 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.


A variety of conditions can damage or injure the muscles and the fibers themselves and result in true 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: The 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 — conditions where the immune system attacks itself, including muscles — and also from infectious causes such as bacteria, viruses and fungi [3].
  • 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.


People with a variety of systemic disorders may interpret difficulties performing certain tasks as weakness. This type of weakness is more related to fatigue and is not considered true weakness. These systemic disorders include conditions such as cardiopulmonary disease, joint disease, anemia, malignancy, chronic infectious or inflammatory disease, and/or depression. People with any of these conditions may be functionally limited, and the lack of use of the affected limb or muscle may progress to true muscle weakness due to deconditioning (infrequent use of the muscle).

A.I. Health Assistant Causes for Weakness in One Upper Arm

The list below shows results from the use of our A.I. Health Assistant by Buoy users who experienced weakness in one upper arm. This list does not constitute medical advice.

  1. 1.Brachial Plexopathy (Shoulder Nerve Issue)

    The brachial plexus is a complex nerve network located in the upper chest and shoulder region. Nerves can be explained as 'electric wires' of the body, passing through signals from the brain to the spinal cord and from the spinal cord to the muscles. The brachial plexus is a bundle of nerves that lies deep to the collar bone, which supplies the shoulder, arm, forearm, and hand. When this bundle of nerves is (partially) damaged, one speaks of a 'plexopathy'. Several causes of damage can be injury or forceful trauma, inflammation or infection. A commonly known cause is sports injury in contact sports like football and rugby. Symptoms can include pain, burning, numbness and weakness in the shoulder and arm on one side, sometimes shooting through the arm to the hand. An acute (sports) injury that causes this condition is often called 'burners' or 'stingers' because of the burning and stinging type of pain. When the cause is inflammation of the nerves, it is often called the Parsonage-Turner syndrome.

    The severity of this condition is highly variable, and dependent on the amount of damage caused to the nerves. Brachial plexus injury following surgery usually has a good prognosis. Recovery times range from 2 weeks to 2 years.

    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
    Primary care doctor
  2. 2.Repetitive Strain Injury of the Upper Arm

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

    Resolves with rest

    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
  3. 3.Rhabdomyolysis

    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.

    Most patients recover in a few days but occasionally will need prolonged hospital care if the kidneys are injured.

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

    Weakness in One Upper Arm Checker

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  4. 4.Stroke or Tia (Transient Ischemic Attack)

    A stroke is a medical emergency. Strokes happen when blood flow to the brain is stopped.


    Top Symptoms:
    dizziness, leg numbness, arm numbness, new headache, stiff neck
    Symptoms that never occur with stroke or tia (transient ischemic attack):
    bilateral weakness
    Emergency medical service
  5. 5.Amyotrophic Lateral Sclerosis (Als)

    Amyotrophic lateral sclerosis is also known as ALS or Lou Gehrig's disease. This progressive, neurodegenerative disease affects nerve cells.


    Ultra rare
    Top Symptoms:
    shortness of breath, decreased exercise tolerance, difficulty concentrating, difficulty walking, hoarse voice
    Primary care doctor
  6. 6.Pinched Nerve in the Neck

    With age, disks separating the cervical vertebrae (which are the bones of your spine in your neck) lose height as well as lose water content, becoming stiffer. The vertebrae move closer together, and nerves that exit between these bones may be pinched, causing pain to travel down the nerve as it passes through the arm. The pain is usually sharp, and some people report a "pins and needles" sensation or even complete numbness.

    Majority of patients get better with time (weeks to months).

    Top Symptoms:
    pain in one shoulder, spontaneous shoulder pain, pain that radiates down arm, pain in the back of the neck, severe shoulder pain
    Primary care doctor
  7. 7.Rotator Cuff Tendonitis

    Impingement syndrome is a common shoulder condition seen in aging adults. The tendons of rotator cuff muscles, whose action is to rotate the arm such such as during a tennis swing, pass in a narrow space between two bones in the shoulder. When the space becomes too narrow, which can happen as a result of an overuse injury, pain may develop as the tendons rub against the bones.

    Impingement may take weeks to months to settle.

    Top Symptoms:
    pain in one shoulder, dull, achy shoulder pain, shoulder pain that gets worse at night, difficulty moving the shoulder, shoulder pain from overuse
    Symptoms that always occur with rotator cuff tendonitis:
    pain in one shoulder
    Primary care doctor

Weakness in One Upper Arm Treatments and Relief

Treatment for weakness in the upper arm is largely focused on physical rehabilitation and therapy. The causes of upper arm weakness discussed above can have specific treatments (for example, antibiotics for certain infectious causes or steroids for inflammatory etiologies); however, once the upper arm weakness results, treatment must be based in physical therapy in order to restore strength, function, and mobility to the arm.

FAQs About Weakness in One Upper Arm

Here are some frequently asked questions 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 there are many factors that may contribute to the restoration of function such as age and severity of the disease.

What are the signs of a stroke?

The mnemonic or phrase FAST is a good way to remember the signs of stroke and what to do in such a situation [4]. Facial droop, arm weakness, and speech difficulty are all signs that it is Time to call 9-1-1 (in the USA) or another emergency responder. Strokes are medical emergencies that 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 by you, the patient. A grading system from zero to five is often used and documented as the following [1]:

  • 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.

Questions Your Doctor May Ask About Weakness in One Upper Arm

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

If you've answered yes to one or more of these questions, try our weakness in one upper arm symptom checker to find out more.

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Weakness in One Upper Arm Symptom Checker Statistics

  • People who have experienced weakness in one upper arm have also experienced:

    • 19% Pain in One Shoulder
    • 6% Pain in One Arm
    • 4% Pain in the Upper Arm
  • People who have experienced weakness in one upper arm had symptoms persist for:

    • 39% Over a Month
    • 22% Less Than a Day
    • 18% Less Than a Week
  • People who have experienced weakness in one upper arm were most often matched with:

    • 63% Rhabdomyolysis
    • 27% Brachial Plexopathy (Shoulder Nerve Issue)
    • 9% Repetitive Strain Injury of the Upper Arm
  • Source: Aggregated and anonymized results from visits to the Buoy AI health assistant (check it out by clicking on “Take Quiz”).

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  1. Miller, ML. Approach to the patient with muscle weakness. UpToDate. Updated June 13, 2017. UpToDate Link
  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