The Shoulder Joint

Editor's Note: When you see these three dots surrounded by a gray rectangle — 1 — you can click on it to get further information about the topic. Click a second time, and the message goes away.

This article was edited and updated on May 10, 2017.

A Complex Joint

The shoulder and the hip are the two most complex joints of the body. The shoulder joint is the most mobile of all of the joints, yet the least stable. It is particularly troublesome when it’s been injured. Just consider all the various ways a normally functioning shoulder can move, and you will understand how quickly it becomes a problem when it can’t.

The shoulder is a ball and socket joint — that is what allows its great movement and flexibility. No less than nine muscles originate from the pectoral girdle and cross the shoulder joint to insert on the humerus. The primary movers are the Pectoralis major, the latissimus dorsi, and the deltoid muscles. The remaining muscles act as stabilizers. 2

Muscles of the Shoulder

Pectoralis major is a large fan-shaped muscle which stretches across the upper chest on both sides of the sternum. Its fibers begin in the sternum, the clavicle (collar bone) and the cartilages of Ribs 1-6. All of its fibers come together and insert on the humerus at a special groove. This large muscle helps you to flex your arm. It also adducts and medially rotates the humerus, as well as elevates the rib cage. This muscle is key in any pushing or throwing movements. See also: Pectoralis Major: The Pecs

Latissimus Dorsi (often referred to as “the lats”) is a large, flat muscle of the mid-lower back. It begins in several levels of vertebrae, as well as 3-4 ribs and part of the pelvis. It moves in a spiral fashion into the same groove of the humerus where the Pectoralis major goes. Latissimus Dorsi is a very powerful muscle; it is useful in adduction and medial rotation of the humerus; it also extends the shoulder joint. It is a primary mover in downward movements of the arm; it is particularly important in sports such as swimming and climbing. See also: Latissimus Dorsi: The Lats

The three Deltoids form the thick muscle that gives roundness and mass to the shoulder. They begin at the lateral portion of the clavicle and two parts of the scapula. Like Pec Major and the lats, they insert into the humerus. When all three deltoids act together, they abduct the arm. But individually, they also help with flexion, medial rotation of the humerus, extension, and lateral rotation as in arm swinging. See also: The Deltoids

Teres major begins on the posterior surface of the scapula and inserts, after joining with the latissimus dorsi into the intertubercular groove of the humerus. Working with the other major muscles of the shoulder, Teres major adducts and medially rotates the humerus; it also extends the shoulder.

This small muscle in the drawing at the left — Coracobrachialis — helps you to flex and adduct the humerus.

The final set of muscles which affect the shoulder are the rotator cuff muscles: Supraspinatus, Infraspinatus, Teres Minor, and Subscapularis.

Supraspinatus, perhaps the most important of the four, stabilizes the shoulder joint and prevents downward dislocation of the humerus when carrying a heavy weight. Infraspinatus and Teres Minor hold the head of the humerus when lateral rotation of the humerus occurs, and Subscapularis works with pec major as a primary medial rotator of the humerus. When this group of muscles gets injured, recovery can be a long, slow process. Surgery is sometimes required.

Some Common Injuries of the Shoulder

Here are some of the most common injuries of the shoulder:

Early detection is the key to preventing serious injuries in the shoulder. Seeing your doctor (and specialists) to assess the damage and prescribe the proper remedies is imperative.

Some Exercises for Stabilization of the Shoulder Joint

Some general rules first:

Front Raise with Free Weights

Front Raise (anterior deltoid): Stand tall and put arms down at side with palms facing back. Lift arms to front, keeping elbows extended and shoulders relaxed. Do not go above shoulder level. Return to starting position.

External Rotation (infraspinatus, teres minor): Bend arms and with palms up place elbows in at waist. Move hands and only the lower arm out to side, keeping elbows bent and close to waist. Return to starting position and repeat.

Bicep Curl with Free Weights

Bicep Curl (biceps): Stand tall with shoulders relaxed and put arms to side with palms facing forward. Bend elbows and lift hands and lower arms up to shoulder. Lower arms back down to side.

Lateral Raise with Elbow Bent (middle deltoid, supraspinatus): Begin with straight arms at side, palms facing back. Bend elbows and bring to your waist with hands out and palms down. Then lift the elbow up to shoulder height and lower back down to waist.

Shoulder Press Above Head with Free Weights

Shoulder Press Above the Head (anterior deltoid, upper trapezius): Stand tall and place arms at the side with palms facing in. Lift arms so elbow is bent at 90-degrees, then straighten arm until hands are overhead and elbows extended. Return to shoulder for the next repeat of the movement.

Lateral Raise (middle deltoid, supraspinatus): Hold arms at side with palms turned in. Lift arms out to sides. Do not go above shoulder level. Return to starting position.

Tricep Extension Overhead with Free Weights

Tricep Extension Overhead (triceps): Lift one arm straight up, then bend at the elbow and have hand touch the back of your neck. Hold, and then bring arm down and repeat with the other arm.

Triceps Extension at the Side with Free Weights

Lat Pulldown (latissimus dorsi, triceps): Place arms straight out at shoulder height, palms down and about shoulder distance apart. Keep one arm straight and move the other hand back to your shoulder and hold. Return to the starting position and repeat with other arm.

Triceps Extension at the Side (triceps, rhomboids): Place one foot forward, keep both feet straight. Place hands at hips with elbows bent. Bend slightly at the hips. Extend elbow and move the arms back. Return to waist.

Shoulder Extension (triceps, latissimus dorsi, lower trapezius, rhomboids, posterior deltoid): Stand tall with hands at side, palms turned in. Keep elbow extended and move arm straight back. Hold and then return to starting position.

You may also wish to read some of these related articles:

Anatomy Charts courtesy of FCIT.

I am a BCRPA-certified fitness instructor in Vancouver, BC. I teach four classes at the West End Community Centre in Vancouver, BC, mostly designed for the older adult. The Inevitable Disclaimer: Everything published here expresses only my opinion, based on my training and research. What you do with the information is entirely your own responsibility. I am not liable for any injury you suffer that seems to be related to anything you read here. Always consult your doctor before beginning an exercise program. For other articles, return to the table of contents.

★ ★ ★

  1. These three dots behave exactly like a footnote. Click on them and you will get more information about the topic. 

  2. As you read through this article, link to the Fitness Term Dictionary to check out the meaning of movements terms such as flex and extend.