Shoulders 101: Everything You Need to Know

The bones in the shoulder form a girdle shape. The shoulder girdle, or pectoral girdle, is comprised of two bones: the scapula and the clavicle. The scapula, or shoulder blade, is a triangular-shaped bone that rests on the upper back, with the lower tip pointing down toward the sit bones. Along the top edge of the scapula is a long, thin ridge called the spine of the scapula. The spine of the scapula extends all the way out to the tip of the shoulder and curves around slightly toward the front of the body, where it attaches to the clavicle, or collarbone. The clavicle is a long, thin bone that extends along the top of the chest and connects at the sternum, or breastbone, in the center.

The outer, upper corner of the scapula forms a small soap dish-shaped surface called the glenoid fossa (about an inch below where the clavicle and spine of the scapula meet). The head of the humerus, or top of the arm bone, rests in the glenoid fossa to form the shoulder joint.

The shoulder, like the hip, is a ball in socket joint. The glenoid fossa of the shoulder joint is significantly shallower than the acetabulum (socket part of the hip joint). For this reason, the shoulder joint has a significantly larger range of motion than the hip joint. In fact, the shoulder is the most mobile joint in the entire body. A group of muscles called the rotator cuff supports and protects the shoulder joint.

Interestingly, the movements of the shoulder joint (where the head of the humerus meets the glenoid fossa) and the movements of the scapula on the back can be separated from each other, though they often work together to perform a given task.

The movements of the shoulder joint (or glenohumeral joint) include flexion, extension, abduction, adduction, medial rotation, lateral rotation, and circumduction.

Flexion is when you lift the arm up toward the front, like when raising your hand in a classroom. Extension happens when you lower your arm back down from flexion or when you lift your arm to the back, like the back swing in bowling.

You are abducted at the shoulder when you raise your arms out to the sides like you would to keep your balance walking on a tightrope. The shoulder joint is adducted when the arms are glued down to your sides.

Medial rotation occurs when you rotate the arm inward toward the body. Lateral rotation is the exact opposite, where the arm rotates outward around toward the back. If you stand with your arms reaching out to the sides (in abduction) with fingers spread out, the arm is in medial rotation when the thumb points down, and in external rotation when the thumb points up or slightly back.

Finally, if you keep your arms parallel to the ground and move them from flexion to abduction and back, that is called circumduction. When umpires make the sign for “safe,” their arms are circumducting.

The movements at the scapula include elevation, depression, upward rotation, downward rotation, protraction, and retraction.

Elevation is when the shoulders move up toward the ears, like when you shrug. Depression is when the shoulder blades press down, creating as much space as possible between the shoulders and the ears.

Upward rotation is when the lower tip of the scapula moves away from center and up. This movement is usually happens with flexion or abduction of the shoulder, like when you reach for a can of soup on the top shelf in your pantry. Downward rotation is when the lower tip of the scapula moves toward center. This happens most during extension or adduction, like when you put your hand into your back pocket.

Protraction is when the scapulae move away from each other, the shoulders come forward, and the chest becomes somewhat concave. Your shoulders are protracted if you hug yourself when it is cold out. Retraction is when the scapulae move toward each other, the shoulders move back, and the chest protrudes forward. You retract your scapulae when you reach behind yourself to pull on a coat.

You’ve probably heard the term “holding a lot of tension in their shoulders.” But what does that really mean?

Because the shoulder has such incredible mobility, it is often rather unstable. The brunt of the stabilization work falls onto the muscles that surround the joint, since the joint structure allows for a great range of motion. Typically, injuries and other maladies are the direct result of an imbalance or misalignment somewhere in the body. As a culture, we spend a lot of time sitting at a desk or computer. The tendency, while seated, is to slouch and slump our shoulders forward. When the shoulders are constantly asked to “rest” in a shape where the bones are not in their natural alignment, the connective tissue around the joint becomes dehydrated and stiff, decreasing the range of motion. When the shoulders are in a slouched position, some muscles are always contracting while others are always stretching. After a lot of time in a slouched position, the muscles that are constantly stretched become strained and can begin to spasm or cramp. This leads to what are often referred to as knots (this is the tension part!) in the shoulders.

Beyond “tension in the shoulders,” the body is designed with a certain amount of space in each joint. When the shoulders are slouched, the space in between the bones in the shoulder girdle decreases, causing friction between the bones, bursas (fluid-filled sacs that act as shock absorbers), muscles, tendons, and ligaments, and may even compress the nerves. All of these imbalances can lead to serious injuries and ailments, not just in the shoulders, but also in the arms, head, neck, and spine.

Align the Shoulders to sustain optimal range of motion, support the strength of the arms, and prevent injury to the shoulders, arms, neck, and spine.

To Align the Shoulders, first pull the collarbone wide—create width between the outer tips of the shoulders without compromising the space between the shoulder blades, then push the shoulder blades down toward the feet—creating space between the shoulders and the ears.

To practice this technique, follow these cues:

1. Inhale; pull the collarbones wide.

2. Exhale; push the shoulder blades down the back toward the feet.

In everyday life, you can Align the Shoulders while carrying a heavy bag. Instead of letting your shoulders slump under the weight of the bag, stand tall and pull your collarbones wide. And then, let the pressure of the bag’s strap remind you to push your shoulder blades down your back toward your feet.

Try our shoulders workout to stretch, strengthen, and optimize the shoulder, and practice our Align the Shoulders technique.

Since the shoulder is the most mobile part of the body, injuries are likely to occur. Common injuries to the shoulder joint include sprains, muscles strains, dislocations, fractures of the collarbone or humerus, rotator cuff tendinitis, rotator cuff tear, shoulder impingement, shoulder bursitis, frozen shoulder, and arthritis.