The Anatomy of the Pectoralis Major Muscle

You have two pectoralis majors or "pecs," one on each side of your chest. These large muscles help you move your shoulder.

These muscles help pull your arm across the front of your body. Injury to the pectoralis major can cause shoulder pain and limit your ability to use your arm fully.

The pectoralis major is superficial, making it easy to see and palpate (feel). If you place one hand on the front of your shoulder and slide it in toward your breast bone, your pecs reside under the layer of fatty tissue or breast tissue of your chest.

Anatomy

The pectoralis major is a fan-shaped muscle in the front of your chest wall. The muscle has two heads: the clavicular head and the sternocostal head.

Location

The clavicular head originates from the front of your collar bone (medial clavicle), then continues down your upper arm bone (humerus) where it attaches at the intertubercular sulcus.

The sternocostal head originates from your breast bone (sternum), the upper six costal cartilages of your ribs, and your external oblique muscle. The sternocostal head attaches to the humerus with the clavicular head.

Nerves and Blood Supply

The pectoralis major muscle is supplied with nerves (innervated) from the brachial plexus.

• The upper part of the muscle is innervated by the lateral pectoral nerve that comes from cervical levels five, six, and seven.
• The lower part of the pec is innervated by the lateral and medial pectoral nerve from cervical levels five, six, seven, eight, and thoracic level one.

The blood supply to the pectoralis major comes from the pectoral branch of the thoracoacromial trunk.

Function

The pectoralis major helps you pull your arm across the front of your body (adduction). The muscle also works with your rotator cuff (subscapularis) to allow you to rotate your arm in.

When your arm is fixed or bearing weight, the pectoralis major works with the latissimus dorsi and other scapular stabilizers to elevate your body.

Using your arms to push or using crutches are two examples of when these muscles would work together.

Associated Conditions

While rare, a pectoralis major rupture can happen if the amount of force applied to the muscle overloads the tendon and causes it to tear.

Pectoralis muscle tears are graded according to severity.

• Grade I: Simple overstretching of the tendon
• Grade II: Tendon is overstretched and partially torn
• Grade III: Full-thickness tear of the pectoralis tendon

According to published case studies, the injury is mostly seen in male athletes and is usually associated with weight lifting, particularly the bench press.

Symptoms of a pectoralis major tear include:

• An audible "popping" sound when the injury occurs
• Pain in the front of your shoulder
• Swelling in the front of your shoulder
• Difficulty moving your arm inward or across your body
• A visible or palpable divot in the front of your shoulder
• Bruising in your chest or upper arm

Injuries to your shoulder can also cause problems with your pecs. For example, a rotator cuff tear can place excessive stress on your pectoralis major, and a frozen shoulder can adaptively shorten the muscle and limit motion.

A pinched nerve in your neck can injure the nerve that innervates your pectoralis major, causing muscle weakness or paralysis.

Sitting with a rounded shoulder and forward head posture can put your pectoralis major muscles in a shortened position. This can make standing and sitting upright difficult and may limit your shoulder's range of motion.

Rehabilitation

If you think you have injured your pecs, you'll need to see your healthcare provider. A correct and timely diagnosis is the first step to treating a pectoralis major injury.

If you injure your pectoralis major, you will need to rest and not move your shoulder (immobilization). This will give the tendon time to heal. The length of the initial rest period will depend on how severe the injury is, but 3 weeks is about average.

You may need to wear a sling to keep your shoulder from moving and in an optimal position for healing.

You may need to have surgery to repair the injury with weeks or months of rehabilitation to recover.

Resuming Activity

After a period of rest, you'll be able to start lightly moving your arm. Gently stretching your pec muscles can help improve mobility around the tendon.

A physical therapist will likely be an important part of your recovery. They can show you which movements will be best for your healing shoulder, such as gentle, range of motion exercises.

They may also recommend exercises to help restore shoulder and arm mobility, such as:

• Shoulder pulleys
• Corner pec stretch
• Have you use a towel to stretch your pecs

Gentle loading of the pectoralis major can also be part of rehab for pec tears. These exercises may include internal shoulder rotation with a weight or resistance band, which helps to gradually increase the load-bearing tolerance of the injured muscle.

For these exercises, you'll progress slowly to avoid injury. Full strength should be achieved before attempting a dumbbell or barbell chest press.

Shoulder injuries that can cause pectoralis tightness may require you to stretch both the shoulder and your pec muscles.

If a pinched nerve is causing your pectoralis major weakness, the first step is to take the pressure off the nerve. Pinched nerves usually come from your spine, often as the result of a bulging disc or spinal arthritis.

Your physical therapist can show you exercises that can help free the nerve. Once the nerve is no longer pinched, you can start gradually strengthening your pecs with resistance bands, body weight, or dumbbells.

A Word From Verywell

If you've injured your pectoralis major, the first step in treating the injury is to rest. You may also need to have surgery. Once the muscle has had time to heal, working with a physical therapist will help with proper healing, and improve the range of motion and strength in your shoulder, while avoiding further injury.