Sternocleidomastoid (SCM) Muscle

What is the sternocleidomastoid (SCM) muscle?

The sternocleidomastoid muscle (pronounced “stur-nuh-klai-duh-MAA-stoyd”) is the largest muscle in the front of your neck. It’s located just below your skin. You can use your fingers to feel it on both the right and left sides of your neck. You can feel your pulse through your SCM muscle.

It’s a paired muscle (two parts). Your SCM muscle starts at the bottom of your neck, wraps around both sides and ends at the base of your skull. It gets its name from its location and its parts.

• Sterno means your sternum, or breastbone. One part of the SCM muscle (the sternal head) begins at your breastbone. It travels up both sides of your neck, where it merges with the other part of the SCM muscle, the clavicular head.
• Cleido means your clavicle, or collarbone. The other part of the SCM muscle (the clavicular head) begins in the center of your left and right collarbones. It travels up both sides of your neck and merges with the sternal head.
• Mastoid is short for a section of bone called the mastoid process. The mastoid process is located at the base of your skull behind your ears. The SCM muscle ends at the mastoid process.

What does the SCM muscle do?

Your sternocleidomastoid helps you bend your neck and turn and tilt your head. It activates when you:

• Turn your head to face left or right.
• Tilt your head toward your right or left shoulder.
• Tilt your head backward, chin up.
• Tilt your head forward, chin to chest.

Your SCM muscle also helps you:

• Maintain your posture. It helps stabilize your neck even when you’re not moving.
• Breathe. It works with other neck muscles to lift your breastbone and collarbone when you inhale. The movement creates space for your lungs to take in air.
• Chew. It supports the joint that connects your jaw to your skull called the temporomandibular joint (TMJ). The TMJ allows you to open and close your mouth.

Where is the SCM muscle located?

The SCM extends from the base of your skull (mastoid process) and down both sides of your neck until it ends at your sternum (sternal head) or clavicle (clavicular head). The muscle is wider and thinner where it starts and ends. It’s narrow and thicker in the middle where the sternal and clavicular heads merge.

The SCM muscle borders two neck regions known as triangles. The inner part of the SCM muscle bounds part of the anterior triangle. “Anterior” means near the front. The outer part of the SCM muscle bounds part of the posterior triangle. “Posterior” means toward the back.

The triangles contain important nerves, blood vessels, lymph nodes and glands. Healthcare providers sometimes use the SCM muscle as a reference point to locate these structures for surgery.

What does the SCM muscle look like?

Viewed from the front, imagine the SCM muscle as a short, untied scarf that hugs both sides of your neck. It doesn’t extend beyond your breastbone (where the sternal head begins) or collarbones (where the clavicular head begins). The left and right sides gradually come closer together as they travel down your neck to the bones in your chest, but they never meet.

What is the SCM muscle’s structure?

The SCM muscle consists of parallel rows of muscular fibers. The majority (about 60%) are white anaerobic fibers. The rest (about 40%) are red aerobic fibers.

“Aerobic” and “anaerobic” describe how the fibers use oxygen for energy. Generally, white fibers are more powerful and can make stronger contractions, but they tire more quickly than red fibers. With age, the number of red fibers relative to white fibers increases.

There are slight differences in structure between the sternal and clavicular heads of the SCM muscle:

• The sternal head is a rounded bundle of skeletal muscle and tendon. It produces more powerful contractions.
• The clavicular head is a mix of muscular and fibrous tissue.

What are the common conditions and disorders that affect the SCM muscle?

As with any muscle, injuries, sprains, strains, atrophy (wasting away) and tumors can damage your SCM muscle.

Conditions that involve your SCM include:

• Sternocleidomastoid syndrome: An acute or chronic (long-term) condition involving neck stiffness, pain and other symptoms. It happens when part of your SCM muscle develops tightened, sensitive areas, or trigger points. The SCM muscle’s size and complexity make it susceptible to strain and injury. As a result, trigger points may develop in multiple places within the muscle.
• Temporomandibular joint disorders (TMD). TMD occurs when the muscles and ligaments that support your TMJ become irritated or injured. While not all TMD is associated with your SCM muscle, problems with your SCM muscle can cause pain associated with TMD.
• Torticollis (wryneck): Short, tightened SCM muscles can cause your head to naturally turn or tilt to one side. There are different types of torticollis, but it’s usually present at birth.

Where do you feel SCM pain?

You may feel a dull or sharp pain within your SCM muscle. Commonly, people experience referred pain. This means that although the pain starts within the SCM muscle, you feel it in a different place.

The SCM muscle may cause pain in your:

• Face.
• Forehead.
• Eyes.
• Cheek.
• Ears.
• Sinuses.
• Throat (when you swallow).
• Shoulders.

Other symptoms

Other symptoms of a condition affecting your SCM muscle include:

• Headache.
• Dizziness.
• Vertigo.
• Nausea.
• Eye changes (droopy eyelid, red or watery eyes, blurred vision).
• Neck stiffness (including trouble tilting or turning your head).

What are common treatments for the SCM muscle?

Treatments include:

• Hot or cold therapy to ease inflammation and pain.
• Stretches to strengthen and lengthen muscle fibers.
• Massage to relax and release the muscle.
• Osteopathic manipulation treatment.
• Physical therapy.

You may need surgery on your sternocleidomastoid if more conservative treatments haven’t worked and you’re experiencing pain. You may need surgery if there’s severe structural damage, like a major tear or a tumor that’s damaged tissue.

How can I keep my SCM muscle healthy?

To care for your SCM muscle:

• Manage stress and anxiety. Minimize the tension you carry in your muscles from stress and anxiety. Regular exercise and sleep, yoga and meditation are all good options for managing stress, but there are many others.
• Practice good posture. This includes positioning digital devices like cell phones and computers so you’re not craning your neck to use them. Don’t strain your neck when you’re reading.
• Support your neck during sleep. Sleep on your back with a pillow supporting your neck. Avoid sleeping on your stomach.
• Raise your head slowly during sit-ups. You activate your SCM when you do sit-ups. Sudden movements can injure it when you’re already straining to pull your body up.
• Stretch. Daily neck stretches are a good idea, especially if you sit most of the day at work. If you have a job that requires you to maintain an uncomfortable posture for long periods, speak with your healthcare provider about stretches that can protect your SCM muscle. For example, violinists, painters and carpenters work in positions that can strain the SCM muscle over time. Proactive stretching can reduce the risk of an injury.

A note from Cleveland Clinic

Your sternocleidomastoid works alongside the deeper structures in your neck to provide support and ease of movement. Stretching your neck regularly and taking steps to manage stress can help prevent tension and strain that can lead to stiffness and pain in your SCM muscle.