Deltoid Muscles

Your deltoid muscles cover the top of your shoulder. They help you lift your arm to front, side and back. Deltoid muscle pain can affect swimmers, pitchers or anyone who performs repetitive overhead arm movements.


What are deltoid muscles?

Your deltoid muscles are in your shoulder, which is the ball-and-socket joint that connects your arm to the trunk of your body. Deltoid muscles help you move your arms in different directions. They also protect and stabilize your shoulder joint.

Like most other muscles in your body, the deltoids are skeletal muscles. Tendons attach them to bones. Skeletal muscles are voluntary muscles, meaning you choose to move them. Skeletal muscles are different than smooth, or involuntary, muscles (such as your heart) that work without you having to think about it.


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What is the purpose of the deltoid muscles?

Your deltoid muscles work alongside your other shoulder muscles, such as the rotator cuff muscles, to help you perform a variety of movements. Deltoid muscle functions include:

  • Arm abduction, which means raising your arm out to the side of your body.
  • Compensation for lost arm strength if you have an injury, such as a rotator cuff tear.
  • Flexion (moving your arm forward, toward an overhead position) and extension (moving your arm backward, behind your body).
  • Stabilization of your shoulder joint to prevent dislocations as you lift your arm or while you carry weight with your arms at your side.


Where are the deltoid muscles located?

Your deltoid muscles crown your shoulder, covering the front, side and back of the joint. They’re superficial, which means they’re close to the surface of your skin. The deltoid looks like an upside-down triangle. Tendons connect each of the three side to bones.

The base of the deltoids connects to the upper part of your scapula (shoulder blade) and the side of your clavicle (collarbone). The point of the deltoids attaches to the side of your humerus (the arm bone between your shoulder and elbow).


How are the deltoid muscles structured?

The deltoid muscles have three parts, or heads:

  • Anterior deltoids: The front delts that help move your arm forward. They connect to your clavicle. You use your front delts if you reach for an object on a shelf.
  • Lateral deltoids: Side delts that help move your arm out to the side, as well as up and down. They connect to your acromion, a bony nob on your shoulder blade. You use your side delts if you do jumping jacks.
  • Posterior deltoids: Rear delts that help move your arm backward. They connect to the flat surface of your shoulder blade. You use your rear delts if you pitch a baseball.

What are the deltoid muscles made of?

Like other muscles in your body, deltoid muscles in your shoulder contain elastic fibers. These fibers make the muscles flexible, so they can perform lots of movements. Skeletal muscles are red and white, making them appear striated (striped or streaked).


Conditions and Disorders

What conditions and disorders affect deltoid muscles?

Conditions that may affect your deltoid muscles include:

  • Adhesive capsulitis: This condition occurs when the capsule around your shoulder joint gets thick and stiff. It can cause shoulder pain, muscle spasms and stiffness. Another name for adhesive capsulitis is frozen shoulder.
  • Axillary nerve palsy: The axillary nerve supplies sensation to the deltoid muscle. Compression of or damage to the nerve can happen during surgery or due to a traumatic injury or overuse of a crutch. These issues can lead to shoulder weakness or numbness, especially around your deltoid muscle.
  • Bursitis: Shoulder bursitis is inflammation of the bursa (tiny, fluid-filled sacs) in your shoulders. The inflammation can make it hard to move your shoulder joint. It may also cause muscle irritation.
  • Deltoid fibrosis: Repeated shoulder muscle injections can lead to fibrosis. This condition causes the muscle to stop repairing itself. You may experience deltoid muscle pain or loss of muscle strength and mobility.
  • Rotator cuff tears: Sometimes severe rotator cuff tears damage or dislocate the deltoid muscle.
  • Shoulder impingement syndrome: Your shoulder muscles or tendons rub against bones. This friction, called shoulder impingement syndrome, leads to joint pain and inflammation.
  • Shoulder separation: A separated shoulder happens when the ligaments tear between the collarbone and the shoulder blade. In severe cases, surgery may be necessary.
  • Strains and overuse injuries: A shoulder strain is the result of overstretched muscle fibers. Strains can happen suddenly, or they might develop slowly over time due to repetitive overhead arm movements.
  • Tendonitis: Shoulder tendonitis occurs when the tendons in your shoulder get inflamed. Tendonitis can cause delt pain or make it difficult for you to use your shoulder muscles or move the joint.

How common are deltoid muscle injuries?

Shoulder muscle conditions are common. One study suggests that 18 to 26% of adults experience shoulder pain at some time in their lives. But problems affecting the deltoid muscles aren’t quite as common as other shoulder conditions, such as rotator cuff injuries.

Who gets deltoid muscle injuries?

Anyone can have problems with their deltoid muscles. But they’re more common in athletes that perform a lot of overhead arm movements, such as:

  • Baseball pitchers.
  • Swimmers.
  • Tennis players.
  • Weightlifters.

Your risk for shoulder muscle conditions increases if you:

What are the symptoms of deltoid muscle conditions?

Deltoid muscle conditions may cause:

  • Difficulty moving your arm in different directions, especially lifting it overhead.
  • Inflammation or swelling.
  • Joint stiffness or instability.
  • Numbness or tingling.
  • Pain at rest or with certain movements.
  • Spasms.
  • Trouble lifting weight.
  • Weakness.

How are deltoid muscle conditions diagnosed?

Your healthcare provider reviews your symptoms and performs a physical exam. They may ask you to lift your arm to the front, side and back, possibly against some resistance. If your deltoid muscles are working properly, your provider should be able to feel the muscle contract when you lift your arm.

If you can’t lift your arm, it doesn’t always mean you have a deltoid muscle injury. Arm muscle weakness can also be the result of:

  • Cachexia, or extreme muscle loss due to disease or a poor diet.
  • Neuromuscular disorders or myopathies (muscle disorders).
  • Side effects from a vaccine.
  • Your provider may also recommend imaging exams. You may have an X-ray, MRI, ultrasound or CT scan if they suspect any bone fractures, dislocations or tissue tears in your shoulder. An electromyogram (EMG) studies how well your muscles and nerves are working.

How are deltoid muscle injuries treated?

Most deltoid muscle conditions heal with nonsurgical treatments, including:

  • Ice or cold compresses to reduce inflammation.
  • Pain relievers or muscle relaxants.
  • Physical therapy.
  • Shoulder exercises to improve strength and mobility.
  • Sling or other supportive garment to immobilize your shoulder.
  • Steroid injections to relieve pain and swelling.
  • Warm compresses to relax muscles.

Serious deltoid muscle injuries, such as a muscle tear, might require surgery. Your healthcare provider may recommend open surgery or minimally invasive arthroscopic shoulder surgery depending on your injury.

What are the risks of deltoid muscle surgery?

Like any surgery, shoulder surgery carries risks of infection, bleeding, blood clots and scar tissue formation. But it’s also important to note that any shoulder surgery can affect your deltoid muscles. Since these muscles run across most of your shoulder and are near the surface of your skin, surgeons often cut through these muscles when they perform rotator cuff repairs, tendon surgeries or other procedures.

Surgical complications specific to your deltoid muscle can include:

  • Axillary nerve damage, which may result in reduced arm mobility.
  • Blood vessel damage, which can lead to edema (swelling from fluid buildup) in your shoulder and upper arm.
  • Detachment of the deltoid muscle from your clavicle, which requires surgical reattachment.


How can I keep my deltoid muscles healthy?

Take care of your deltoid muscles by:

  • Adhering to sport-specific safety guidelines, such as pitch-count limits in baseball.
  • Not putting strain on your shoulder muscles if they hurt.
  • Resting shoulder muscles after performing a lot of overhead arm movements.
  • Stretching and warming up your shoulder muscles before activity.
  • Using proper technique when throwing, swimming or performing other activities that require repeated shoulder movements.

Additional Common Questions

When should I call my doctor?

Contact your doctor right away if you:

  • Can’t move your shoulder or arm.
  • Can’t feel your shoulder or arm.
  • Have severe, sudden pain in your shoulder or anywhere in your arm.

A note from Cleveland Clinic

Your deltoid muscles play an important role in helping you move your arm in different directions. They also stabilize your shoulder joint and protect it from injuries such as dislocations. People who perform a lot of repeated overhead movements, such as swimmers, pitchers or mechanics, are at risk of injuring their deltoid muscles. Most deltoid muscle injuries heal with nonsurgical treatments.

Medically Reviewed

Last reviewed on 09/24/2021.

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