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Understanding your shoulder

I was speaking to a good friend yesterday about how we like to be spoken to about our bodies by health professionals, and how this might differ from other people's preferences. Thankfully, I have the luxury of time with my clients, in which I can attempt to explain things to them at a level that they understand and that is relevant to them (I don't always get that entirely right, but I'm working on it!), but I can't imagine how frustrating it must be as a medical professional who has 10-30 minutes with someone in which to cover assessment, diagnosis, and advice.

One thing I think most people would agree with is that we would like the basic concepts explained, so that we can understand how the specifics apply to us. So consider this a primer on how the shoulder works, so that some of the sensations you experience and movements I might get you to perform (which sometimes don't involve the shoulder at all!) might make a little more sense.

The structure

The shoulder girdle - which may not be what you consider your shoulder - is actually made up of four joints:

  • the sternoclavicular (SC) joint, which is where your collarbone joins your breastbone - it's the part of the shoulder girdle closest to your midline

  • the acromioclavicular (AC) joint, which is where your collarbone joins your acromion, the bony prominence at the top of your shoulder blade - you'll be able to feel and even see this one quite clearly at the top of your shoulder

  • the glenohumeral joint, which is what most of us think of as "the shoulder", and is where your upper arm joins the outside of your shoulder blade

  • and the scapulothoracic joint, which isn't technically a joint at all, but is where your shoulder blade meets the back of your rib cage

So two joints involve the collarbone (clavicle), and three involve the shoulder blade (scapula), which means these four joints can all interact to move the shoulder in a variety of specific ways.

The movements

Different types of joints have different ranges of movement, and in the case of the shoulder several of these joints can combine their ranges of motion to create even more movement.

I'll break these down by joint first:

  • the sternoclavicular joint allows the collarbone to hinge from the centre of the chest, as in shrugging, or rounding your shoulders forward

  • the acromioclavicular joint allows the shoulder blade to hinge from the top of the shoulder; moving the shoulder blade around the collarbone isn't something you will do consciously, but it will assist the same movements as the SC joint

  • the glenohumeral joint is where our arm movements happen; as a "ball-and-socket" joint, it has the greatest range of motion of the four joints of the shoulder girdle, including:

    • flexion: lifting your arms up to the front all the way up overhead

    • extension: pushing your arms back behind your hips

    • abduction and adduction: lifting your arms out to the side and back down across the midline

    • internal (medial) and external (lateral) rotation: rolling your biceps inwards so the point of your elbow faces away from your body, and rolling them outwards so the crease of your elbow faces away from your body

    • circumduction: making a big circle with your arm

  • the scapulothoracic joint allows the shoulder blade to glide along the rib cage during any of the movements performed by the other joints, though the one most of us are most familiar with is the action of squeezing our shoulder blades together and/or sliding the shoulder blades towards our back pockets

As you may have guessed from the anatomy of the joints, movement at one joint will require some degree of movement or stabilisation at one or more of the other three joints. Hence the structure being considered the "shoulder girdle" rather than just one joint being known as "the shoulder".

You might notice that the glenohumeral joint does a lot more types of movement than the others: ball-and-socket joints have the greatest range of motion, but in turn are also the least stable. The depth of the "socket" (which isn't even a socket but a little groove along the edge of the shoulder blade) is very shallow, which allows for this even greater range of motion but, again, makes the shoulder less stable than a joint like the hip.

I know nobody wants to hear than the solution is finding a balance, but there is no getting around the fact that a healthy and happy shoulder requires the right balance of range of motion and stability.

Movers vs. stabilisers

To list the muscles that make movement at the shoulder girdle happen would be to list all the muscles of the torso and many of the neck. Because many of us think of the glenohumeral joint as the shoulder, we tend to think of the deltoids (the rounded muscles hidden by your t-shirt sleeves) as "the shoulder muscles". However, since the entire shoulder girdle runs from your breastbone, across your collarbone, around your shoulder blade and your upper arm, all the muscles that span this area of the upper torso will be involved in any movement of the shoulders and arms.

The thing that is most important to note, in my opinion, is the difference between a mover and a stabiliser (for the purposes of this post, I am referring only to muscles, though obviously there is a collection of ligaments and tendons and cartilage that also serve to stabilise the joints, in various ways).

A mover is, unsurprisingly, the muscle that makes the movement happen. It contracts, which pulls one bone towards another around the joint, and that's movement. It's worth noting, however, that several muscles can be involved: one might start the movement, others might do the middle portion, another might kick in just to take you right up to the end of your range of motion.

A stabiliser does the opposite: it holds the other end (or segments) of the bone in place, so you don't lose control of the movement. So if you think about throwing a punch, for example, it's the muscles at the back of your shoulder staying active and strong that stop you dislocating your own shoulder, and allow you to pull your punch back in and regain your posture.

Needless to say, if your movers are stronger than your stabilisers, your joint is going to be pulled further through the range than it is prepared to go. This can lead to a sudden injury like a dislocation or muscle or tendon tear (a "pulled muscle"), or a longer-term "wear-and-tear" injury to the tendons, ligaments, joint capsule or articular surface (i.e. those other stabilisers I mentioned above, which are sort of the backstop of the joint).

Training the shoulder

If you have had a shoulder injury, you'll know how frustrating it is trying to identify, describe, and avoid the specific actions that aggravate it, and how non-linear the process of trying to strengthen, stretch, and rehab it is. The simplest explanation is that anything that affects the shoulder, affects the whole upper body, but that doesn't help you get started.

There are some key principles, however:

  1. If a joint can't move through its full range of motion, you can't strengthen all the muscles that are responsible for that movement (the agonists).

  2. By extension, you can't stretch the ones that do the opposite movement (the antagonists).

  3. Therefore, the antagonists get tighter, which make it even harder to get the agonists working, so your range of motion gets further reduced, and so on

So the only place to start is by making sure you have a full range of motion. You might first do this with the help of a therapist or trainer who can do the movements for you, or by performing the version of a movement with the least resistance, e.g. lying on the floor rather than standing.

If you don't feel restricted, then it's time to start working on mobility: that's the range of motion where your muscles are actually doing the work. So if you find that you can take your arm all the way up over your head when you're lying on your back, but not when you're sitting or standing, that's a mobility issue. Because mobility implies the use of muscle action, working on mobility means working on your strength. We increase strength by resistance training, but remember that gravity is a form of resistance! So if you can't get your arms up straight overhead when standing (but you can lying down, or using a strap, or if somebody else moves your arm), your first step is not to pick up a dumbbell to get stronger: your first step is to use your own arm as a weight, reaching it up overhead until you are strong enough to hold it there.

Once you have improved your mobility, then you can think about adding resistance by lifting weights or pulling against a resistance band. But be careful: if your joint isn't stable enough in that position with that weight, the body will move itself to where it is more stable. It will do this either by moving the weight (e.g. by reaching up past your nose rather than past your ear), which changes the angles at the joints and therefore the muscles you are working, or it will move your body around the weight (e.g. by arching your back or shrugging the shoulder), which changes the angles at the joints and therefore the muscles you are working - in both cases, you end up strengthening the strongest muscles, reinforcing your most-often-performed movements, and taking yourself further away from that balanced shoulder.

Of course, the above process has to be done for all movements possible at the shoulder girdle! Of course, many movements happen simultaneously (for example all four joints will all move as you reach your arm overhead, and depending on how you move some of them may move through more than one plane) and many muscles won't need to be strengthened individually or with the use of added resistance - simply engaging them to perform another movement safely and strongly will activate and strengthen them in the way they need to be strengthened. The key is not to rush to pick up a weight before you know you can move your shoulder through all its possible actions, with control.

The sidekick

Most of us know that everything in the body is connected, but many of us forget just how important those connections are.

One connection often overlooked in shoulder training is the role of the thorax, or rib cage. We already know that one of the joints of the shoulder girdle is the scapulothoracic joint; so if the "thoracic" part of that partnership isn't working as it is expected to, the "scapulo" part has to pick up the slack - in other words, the shoulder blade has to move more frequently or more intensely than it is supposed to. And that will affect the acromioclavicular and glenohumeral joints, as they both interact with the shoulder blade.

The good news, if this is all starting to sound a bit overwhelming, is that paying some attention to your thoracic spine - that's the parts of your spine that your rib cage is attached to - has so many benefits beyond just helping you train or rehab your shoulder more efficiently: better mobility and flexibility in your thoracic spine can improve breathing (your lungs are in there, and need space to expand into) and will fire up your abdominal muscles whilst promoting greater stability in the lumbar spine (which is an area many people experience pain in).

And a bonus entry

Well, if you're still here, you're probably happy enough for me to briefly mention the wrist.

Wrists are super complex, but right now we're just concerned about their role in the movements of the shoulder. You already get the idea that everything is connected, so it's probably no surprise that if you're lacking movement in the upper arm (i.e. the genohumeral joint), the wrist may join in to gain range of motion; you see this a lot in mid rows in the gym, when we are supposed to be pulling our shoulders and elbows back, but if the shoulder blades don't glide back and down the spine, the elbows flare out and the wrist curls in to try and pull further.

At the same time, trigger points (or "knots") in the shoulder girdle quite often send pain radiating down the arm and into the wrist and fingers, which can feel quite convincingly like a wrist or elbow problem rather than a shoulder problem. Once that starts happening, those areas can tighten up, causing further restrictions and compensations.

It's easy to be frustrated by these endless interconnections, but let's instead marvel at how endlessly adaptive our bodies are. They'll sacrifice comfort and efficiency in one joint to give us the movement we asked for in the one we're paying attention to. So let's respect their process, and learn to love it, and start working with it, rather than against it.


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Emma Gray
Emma Gray
Apr 14, 2021

Really interesting and insightful piece! Thank you for all your support and guidance with my own recovery from a shoulder injury and taking the time to explain my body and most specifically my shoulder to me. This article really speaks to me!

Apr 21, 2021
Replying to

Thank you for your trust throughout your recovery process, and for this lovely comment and all your support 💛

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