Shoulder Muscles

What are shoulder muscles?

Your shoulder is a ball-and-socket joint that allows you to perform a wide range of movements. You use these muscles for actions from throwing a ball to reaching an item on a shelf. Also called the glenohumeral joint, it has more range of motion than any other joint in your body. There are about eight muscles in your shoulder that support this joint. They give it strength, stability and shape.

Your shoulder muscles are skeletal muscles. Tendons attach them to bones. They’re voluntary muscles, meaning you control how they move and work. Some other muscles in your body, such as those in your heart, are involuntary. This means they work without you having to think about it.

What is the purpose of the shoulder muscles?

The shoulder muscles serve a variety of functions, including:

• Holding the bones of your shoulder joint in place.
• Moving your arms up, down, forward and backward.
• Protecting your shoulder joint.
• Rotating your shoulder joint.

Where are the shoulder muscles located?

Your shoulder muscles surround the top of your arm where it connects to your body’s trunk. Tendons connect your shoulder muscles to bones. These bones include your scapula (shoulder blade), humerus (bone between your shoulder and elbow) and clavicle (collarbone).

How are the shoulder muscles structured?

The most important muscles in your shoulder are the four rotator cuff muscles. Together with tendons, they cup the front of your shoulder and:

• Help you raise and rotate your arms.
• Provide structural support to your shoulder joint.

The rotator cuff muscles include:

• Subscapularis: This muscle attaches to the middle part of your scapula and stretches to the bottom part of the ball of your humerus. A bursa (fluid-filled sac) separates the muscle from the scapula to reduce friction (rubbing) against the bone.
• Supraspinatus: This muscle stretches from the top of the scapula to the top of the humerus, at the ball of your shoulder joint.
• Infraspinatus: This muscle stretches from the bottom of the scapula and connects to the humerus behind the supraspinatus.
• Teres minor: This muscle attaches to the side of the scapula and attaches to the humerus beneath the infraspinatus.

Other muscles that support your shoulder include:

• Rhomboids: Two rhomboid muscles stretch from the top of your spine (at the base of your neck) to your scapula. They help you lift your shoulder blade.
• Trapezius: The trapezius (traps) is a large triangular muscle at the back of your shoulder. It helps you lift and lower your shoulder.
• Deltoid: The deltoid muscle is on the outside of your shoulder. It helps you move your arm forward, backward and to the side.

What are the shoulder muscles made of?

Like other muscles in your body, shoulder muscles contain lots of elastic fibers. These fibers give them flexibility and allow them to contract (tighten). They are red and white, so they look striated (striped or streaked).

What conditions and disorders affect shoulder muscles?

The shoulder joint is extremely flexible, so the muscles and other soft tissues around it undergo a lot of wear and tear. This makes the shoulder muscles susceptible to injuries and degenerative conditions, including:

• Adhesive capsulitis: Also called frozen shoulder, adhesive capsulitis occurs when the capsule around your shoulder joint gets thick and stiff. It can lead to spasms, pain and extreme stiffness in your shoulder muscles.
• 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 and may cause muscle irritation.
• Rotator cuff injury: Rotator cuff injuries, such as rotator cuff tears, usually affect tendons but can also involve muscles.
• Shoulder impingement syndrome: If your shoulder muscles or tendons rub against bones too much, the soft tissues might become painful and inflamed. Another name for shoulder impingement syndrome is swimmer’s shoulder.
• Strain: A shoulder strain is the result of overstretched muscle fibers.

How common are shoulder muscle injuries?

Shoulder muscle conditions are common. In 2006, more than 7 million people saw their healthcare provider for a shoulder problem. Approximately two to four million of these shoulder issues involved the rotator cuff.

How can I keep my shoulder muscles healthy?

Take care of your shoulder muscles by:

• Not pushing through shoulder pain.
• Resting shoulder muscles between workouts or periods of exertion.
• Stretching and warming up your shoulder muscles before activity.

When should I call my doctor?

Contact your doctor right away if you:

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

A note from Cleveland Clinic

Your shoulder muscles support and stabilize the most flexible joint in your body. They help you perform a wide range of movements, from brushing your hair to throwing a ball. Since we use our shoulder muscles so much, they’re prone to injuries. You can prevent most shoulder pain by resting your muscles when they feel tired and keeping them strong and conditioned.