Everything You Need to Know About The Shoulder

This article is an excellent place to start if you want a better understanding of shoulder anatomy and movement. It will explain the assembly and mechanics in simple terms, but also provide a solid explanation for how the shoulder works.

It's like the cliff notes for a Shoulder 101 course that will prepare you for future articles aimed to fix your shoulder hang-ups.

Shoulder Anatomy– “The Framework”

First, get to know the bones of your shoulder.  They are the scaffolding that supports the entire structure, similar to a wood frame for a house.

Starting at the ground floor with the rib cage. 

This is the bony structure designed to protect your internal organs and also provides a good place to attach your arms. rib cage

Although, as you will learn shortly, the shoulder is not tightly fixed to the rib cage. There’s only a single bony attachment that allows freedom for the shoulder to glide around the contours of the rib cage.

The rib cage is usually not included in the shoulder discussion, but it dramatically impacts shoulder function. Feel how bending and rotating the spine orients the rib cage differently and changes your shoulder position.

The big take-home is that often the shoulder relies on the body's posture to put it in a position to work most effectively.

But for the classic shoulder bones, it comes down to three that make up the joint.

1. The Clavicle

The first piece is the clavicle, often referred to as the collarbone.  It’s a support beam of sorts, forming the one bony attachment of the shoulder to the frame of the body.


2. The Scapula

Next is the scapula, also called the shoulder blade, or as slag, it's referred to as the scap.  The scapula hangs off the end of the clavicle and against the rib cage, held in place by 17 different muscles.

The scap muscles act as guide wires, pulling the shoulder blade into different positions.  On the outer corner of the triangle is the shoulder socket (you’ll see later, it isn’t much of a socket.)



Before moving onward, move your shoulder blade around a bit.  Notice how the arm moves along with it.  The term used to describe how the scapula and arm move together is scapulo-humeral rhythm. The key word rhythm describes the movement of two things in synchrony.

This is all too important for the shoulder.  The scapula and arm must work together as a team, otherwise, it’s just a half working shoulder. What I’m getting at, is your fix for shoulder pain, or building arm strength, must include the muscles that move the scapula as well.

3. The Humerus


Then there is the arm bone. In medical terms, it's the humerus. It has a ball on the end which attaches to the shoulder socket. The benefit of a ball and socket is lots of movement....but it's not a socket. 

Instead, the head of the arm bone is much larger and often described as a golf ball sitting on a tee.  Again, the advantage of this is freedom of movement!

Holding it Together

Shoulder anatomy is that simple— only three bones!

All held together by “tape and rubber bands.”The tape describes the static stabilizers. Things that don’t move and aren’t all that stretchy. They do a good job of holding things in place, kind of like tape. The most talked-about static stabilizers are the shoulder ligaments and the labrum.

The rubber bands describe muscles and their tendon attachment (technical folks refer to the rubber bands as the dynamic stabilizers.) They hold things together but also lengthen and shorten, which makes the arm move. 

The Shoulder Trade-Off

To summarize everything to this point, the shoulder is made for movement. It can work in many different directions. Along with that, it can go fast, for things like throwing, or it can be strong to lift weights and carry bags of dog food, or it can be exact to catch something tossed your way.

Compared to the hip, it’s much less clunky. Free to wave around like those tube dancers that jive in front of car lots. However, as with anything, there is a trade-off.

All that movement freedom can bring about problems. First of all, it’s prone to become unstable when the things holding it together aren’t working right (remember…tape and rubber bands.) Secondly, just like any complex machine, there are many ways things go wrong.

We’ll get to the breakdowns in other articles, but for now, let’s cover how it works when things go right.

Movement of the Shoulder

There are lots of shoulder muscles. Each one has a specific action and combines with other muscles for additional movements.

But you don’t need to know any of those things! More important are the principles behind shoulder movement. So let’s break those down into small movements and big movements.

Small Movements

Small movements are performed close to your body with loads that aren’t too heavy—everyday tasks like picking up a coffee cup or working at a desk.

The minor moves happen mainly by the ball of the arm moving in the socket. These actions rely on the four smaller shoulder muscles around the joint called the  rotator cuff. They connect in a circular pattern around the ball of the shoulder joint to move it around.

Big Movements

Now things get a bit more complex. As movements progress away from the body or overhead, it requires more moving pieces.  For things like washing your hair, reaching into the backseat of the car, or opening the overhead bin on an airplane, only so much can happen with the ball moving around the socket. To achieve the extra range of motion, the scapula needs to move to free up additional ranges of motion.

For example, reach as far forward as you can, and you should feel the scapula wrap around the body; or pull your elbows back and notice how the scaps squeeze together. There is significant scapula movement to bring your arm overhead. Several muscles pull from opposing sides to pivot the scap for this action to happen. Moving the scap aligns the shoulder blade with the elevating arm bone and creates a stable support structure for the arm.

And do you feel like you’re tight? Are you stuck in your range of motion, even without much weight? That’s often because the scapula isn’t moving enough to allow that range of motion.

Even Bigger Movements

What about moving heavy weight, pull-ups, and throwing fastballs?

There are additional pieces for high-performance.

First off, these moves usually need full ranges of motion. (Yet again! Moving the scap is important.)

Then with the shoulder in the right position, the rest relies on the prime movers. Those are the workhorses responsible for strength and power.  These are the muscles we hit in the gym—things like the pecs, deltoids, and lats.

But the rotator cuff still has an important job to do here too.  The muscles of the rotator cuff keep the arm bone centered inside the shoulder socket.

Summing it Up

Working the remote or eating cheeseburgers doesn’t require too much from the shoulder. If this is your only goal, there probably isn’t much reason to worry. But to have an active life, as you can see, there are lots of working pieces that need to be strong and coordinated.

So when pain pops up, it’s usually because one of the parts isn’t meeting the demands. The future articles in this series will apply this understanding of shoulder anatomy and movement to explain the many shoulder breakdowns and how pain flares ups. And of course, we’ll show you some ways to fix it.