Your pectoralis major is a fan-shaped muscle on your chest. Many people don’t realize that the pectoralis major has two divisions:  the clavicular division and the sternal division. These names refer to the bones near the origin for each portion for this muscle. The clavicular division originates on the clavicle (collarbone) and the sternal division originates on the sternum (breastbone).

Here’s more on this important glamour muscle.

Location

The origin of the clavicular division of your pectoralis major is on the anterior surface of the medial half or two-thirds of the clavicle. This means that this muscle originates from about a third or a half of the way in on the collarbone, then along the rest of the collarbone toward the midline of the body.

The origin of the sternal division of the pectoralis major is from the sternum to the 7th rib and adjacent to the upper 6 costal cartilages. The costal cartilages are the parts of cartilage that connect the sternum to the ribs.

The insertion for the both divisions of the pectoralis major is on the upper shaft of your humerus, which is your arm bone that sits in your shoulder socket. As you push on the tissue on the front of your body near your armpit, you feel your pectoralis major insertion point.

Function

Both divisions of the pectoralis major muscle share 4 roles. All of these actions involve moving your humerus (upper arm bone). They are:

1. adduction. This happens when your arms are straight by your sides.
2. medial rotation. If you feel like your shoulders are rounded forward toward the midline of your body, that is medial rotation at the shoulder.
3. flexion. This happens when you lift your arm in front of your body.
4. horizontal flexion. When you reach your arm straight across your body (like when applying deodorant to the opposite armpit), that is horizontal flexion.

The sternal division of the pectoralis major has additional roles. The Concise Book of Muscles says that it “obliquely adducts the humerus towards the opposite hip.” I believe here they’re talking about bringing your arm across your body toward the opposite hip, similar to fastening a seat belt.

My Flash Anatomy Muscle Flash Cards say that the sternal division of the pectoralis major also “extends a flexed humerus.” I would love to explain this to you, but I have no idea what they mean. If you understand what they’re meaning, drop me a line in the comments.

My Flash cards also point out that, because of the movement of the humerus, the pectoralis major can impact the placement of the scapula. It can depress, protract, or rotate the scapula downward.

Common Dysfunction

When the pectoralis major is tight or weak, it rounds the back and closes off the chest. Sometimes, it can also feel like your shoulders are really rounded forward. With this closed-off position of your chest, it can be very difficult to take a deep breath.

Also, a dysfunctional pectoralis major can inhibit lateral rotation and abduction of the shoulder. Lateral rotation of the shoulder is when you try to rotate your humerus away from the midline of your body. This causes a feeling of broadness across your collarbones. Abduction of the shoulder is when you reach your arm away from the midline of the body.

Restoring or Maintaining Health

If you believe you have sprained, torn, or injured this muscle, please visit your doctor. Your doctor can order all of the appropriate imaging, therapy, and medicine necessary to help you recover quickly.

If your issue is minor (like bad posture) and you want to restore health and function yourself, here are some ideas.

• Pec stretch. Reach your arm out like you’re making a “T.” Bend your elbow. Make sure your palm and your face are facing the same direction. Press your elbow, forearm, and palm against a door frame. Stabilize your scapula as you gently step through. This should give you a good stretch. Don’t forget to do the other side.
• Push ups. Whether you’re doing regular push ups or Pilates-style, push ups will build strength in your pectoralis major.
• Sun salutations. Yoga doesn’t necessary have a pectoralis major-building pose, but anytime you’re completing a Plank–Cobra–Down dog transition, you’re working your pectoralis major.
• Hit the gym. If you’re into strength training, there are a ton of exercises you can do to strengthen your pectoralis major. Bench press and dumbell fly are just two of the exercises that would benefit you.
• Use a tennis ball or lacrosse ball. Feel free to roll around to break up any tight spots or fascial adhesions. I recommend standing and rolling on a wall. It sort of feels odd because you’re so close to the wall, but it’s a lot easier than trying to do this while on your stomach on the floor. Just make sure to keep your arm straight by your side while you roll.

More Information

I consulted The Concise Book of Muscles by Chris Jarmey. Recently, the book updated to its third edition. You can find the newest edition on Amazon.

Also, I consulted my Flash Anatomy Muscles Flash Cards. If you really enjoy anatomy and want a tool to help you locate specific muscles correctly, I highly recommend these flash cards. Because of their thoroughness, I turn to them any time a client comes in with pain.

Here’s a link to buy them on Amazon. If you purchase them from this link, I earn a small commission.

What’s your favorite way to strengthen your pectoralis major? Let us know in the comments below.

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