The acromioclavicular joint, cueing, and perception

 

The shoulder joint is complex. It connects the torso to the arm via four joints; in contrast, the hip joint connects the femur to the torso with one. The four joints comprising the shoulder joint are the glenohumeral joint, acromioclavicular joint, sternoclavicular joint, and  the scapulothoracic joint (Amabile, et.al, 2016). These joints allow the arm to move in a multitude of ways. Interestingly (at least, to me), the cueing of shoulder position often comes from a fixation on what’s going on in the back. “Take your shoulders down and back,” “let your shoulder blades glide on the rib cage,” and “plug your shoulders into your back,” are all cues I have heard in various exercise and movement settings. People that haven’t exercised in years struggle with understanding where the front of their bodies are in space, let alone what’s happening behind them. The first time I tried cueing the shoulder blades with a couple of my clients, I thought they were going to either a) throw something at me or b) walk out and never come back. The amount of frustration they experienced trying to understand how their shoulder blades had anything to do with their arms was valid, and while I jest (sort of) regarding the severity of their responses, it definitely made me wonder if I was approaching shoulder cueing from the wrong side.

Fortunately, I also study somatic lessons, and two years ago, around the time I was questioning my approach, I came across a nifty Feldenkrais lesson that involved arm rotation and the clavicle, which sent me down a rabbit hole, and led me to an alternative way of enhancing a client’s shoulder experience. As you have probably guessed by now, it involves the clavicle, or collarbone, or that long bone underneath the front most of us never think about, tactile feedback, and playing with words. But before I get ahead of myself, a little bit of anatomy.

I should also mention part of the reason the fitness industry focuses on cueing the shoulder from the shoulder blade might be due to the fact most of the research regarding shoulder mobility has been centered around scapular thoracic rhythm, scapula winging, and movement of the scapula during arm movement (Luedwig, et.al, 2004). The fascination with the scapula and its relationship to shoulder mechanics is valid; research suggests the scapula, how it moves, and how it interacts with the thorax is related to shoulder pathologies (Luedwig, et.al, 2004).

The scapula is a triangular, flat bone that rests on the mid back or ribcage area between ribs 2 and 7 (Frank, et.al, 2013). Variations in the size, thickness, and position of the scapula vary. The scapula doesn’t attach to the thorax in the traditional sense. There are no ligaments or capsules allowing for movement; instead, muscles and bursa allow for the sliding which takes place. The subscapularis (a muscle traditionally thought of as a rotator cuff muscle) moves over the serratus anterior what the scapula moves. The serratus anterior is conveniently located on the posterior aspect of the ribcage between ribs 2-7. This isn’t a blog about the posterior aspect of the shoulder girdle, but based on this simple anatomical relationship, one could discern that for the shoulder to work well, the scapula’s relationship with the thorax matters. The scapula can move in a variety of ways to accommodate shoulder motion, including elevation, depression, protraction, retraction, and rotation. When the scapula moves away from the center of the spine and forward on the ribcage, this is called protraction, and is coupled with internal rotation and anterior tilting. When the scapula moves towards the spine, this is called retraction and is coupled with external rotation and posterior tilting. This is what often occurs when we cue the shoulders to move “down and back.” If we instruct someone to maintain that position during a rowing type movement or a pull-up, for instance, think of the limits we are placing on the shoulder joint, and, as we will see in a moment, preventing natural joint motion to occur.

The glenoid fossa of the scapula forms an articulation with the head of the humerus bone, comprising the glenohumeral joint. This is the joint we often think of when we think of the shoulder joint, and is the most mobile joint in the body, with internal rotation of the arm happening almost entirely at the glenohumeral joint (Frank, et.al, 2013). I said above protraction is coupled with internal rotation and anterior tilting. Try this. Reach your arm out in front of you. Move the shoulder blade forward. What direction did your arm naturally rotate, towards you or away from you? Now, hold your arm in front of you. Rotate the arm in, as though you were pouring a cup of water. Do you feel much movement in your shoulder blade while you do that? Maybe you found the arm moved in a little bit when you protracted the scapula. The conclusion might be allowing the scapula to move affects arm position. When you internally rotated the arm in the second scenario, however, you should have felt little movement in your scapula. This might lead to a different conclusion, that the shoulder blade doesn’t need to move for the arm to internally rotate. 

The acromion process of the scapula forms a diarthrodial joint with the distal end of the clavicle involving a capsule, cartilage, and four ligaments (Martistella, et.al, 2014). It’s thin, and we could assume based on it’s proximity to the glenohumeral joint, it probably has something to do with shoulder mobility. The medial end of the clavicle connects with the top portion of the manubrium (the sternum, or breast bone), making up the sternoclavicular joint (Jurik, et.al). Interestingly, this is the only synovial joint between the upper extremity and the axial skeleton. 

These two joints (the acromioclavicular, or ac joint, and the sternoclavicular, or sc joint) contribute to the ability for the arm to reach overhead. During abduction of the arm, the first 30 degrees or so takes place primarily via the glenohumeral joint. After that, the scapula and the clavicle move to allow the arm to continue reaching overhead, with the sc joint and the ac joint contributing at different points in the abduction process (Frank, et.al, 2013). Think about the anatomy. It’s almost like there is this upper loop from your center emanating out to the shoulders. It makes sense both sides of the loop would support arm movement.

Also, consider what happens if you always lock the shoulder blades in place (down and back) when the arm goes overhead. If you never have your client reach overhead and allow the shoulder to move, your client might think he should never let his shoulder move. This would restrict mobility options in the long run. (To be clear, I am not talking about pressing weight overhead. I am talking about taking the arm overhead in basic, unweighted mobility drills).

Try this. Place your left hand on the clavicle. Now reach your arm in front of you. Did the clavicle move? Keep your hand there and reach your arm all of the way overhead. What about now? In healthy shoulders, the clavicle retracts during shoulder flexion (Ludewig, et.al, 2004). You will also be able to feel movement in your clavicle during protraction and retraction of the scapula. (Look at the anatomy. This makes sense. When you move the scapula, the clavicle will be affected). 

Okay, so the clavicle works with the scapula to produce shoulder mobility. Why does it matter? I am going to argue it matters because of perception, and how people experience movement is largely impacted by their perception of how the movement takes place.

First, to be clear, if you work with the general population, chances are slim most new clients that haven’t been active recently are in tune with their shoulder blades. There is a strong likelihood they aren’t really sure what their shoulder blades are or why they have them, let alone how they work when it comes to shoulder movement. And yet, when we are teaching people skills that involve the shoulder joint, things like push-ups, pull-ups, rows, or even more basic things like planks, down dog, or a simple hands and knees position, we try to make people do things with their shoulder blades. “Broaden your shoulder blades,” “don’t let your shoulder blades come together,” “bring your shoulder blades together” or the cringeworthy “squeeze a pencil between your shoulder blades during your row.” What do people do when they hear these cues? They move their backs (and not always the thoracic spine. I have seen interesting things happen in the neck and lower back during classes when people are trying to make sense of how the scapula can be moved in relation to another body part). This has to do with their perception. There is a basic understanding the shoulder blades are located on the back of the body. To move the shoulder blades must have something to do with the back of the body. And so the brain makes the next logical conclusion: move the back of the body (unless the teacher or trainer has spent time using a somatic awareness drill in supine to draw attention to the shoulder blade and how it moves. The feedback from the floor increases somatosensory awareness and makes it easier for the student or client to translate that information into other positions). 

Enter understanding how the clavicle works. Here is the cool thing about the clavicle. You can touch it and feel how it responds to movement. You can also trace it out to the end of the shoulder and imprint where it actually is in space. From a client or student perspective, this enhances self-awareness and gives the student something tangible to work with during cueing. For instance, there is a 5-8 minute clavicle awareness drill I frequently do with clients struggling with shoulder mechanics. This requires the client to feel via touch how the clavicle moves during internal and external rotation. (I use this after I ask, “can you feel what your collarbone does when you rotate your hand up?” When the answer is no, we do this drill).* Once the connection is made that yes, the collarbone does move and I’m not making things up, it enables me to say things like, “broaden your collarbones,” or “imagine your collarbones reach past your shoulders.” My experience with these cues has been they allow the client broaden across the chest without pulling the scapula off the back. This is different than cueing “chest up,” which also tends to result in a more rigid posture (at least in my experience). There is a time and a place for teaching the client how to lift the chest, but that’s not the conversation we are having today.

Cueing and perception in the training and movement science world is interesting to explore. How clients interpret a cue is dependent upon a) self perception and b) what the words said mean to them. Alain Berthoz writes, “The brain labels its perceptions according to its intentions and goals,” (1997). Doesn’t it seem like it would be beneficial if the intentions were occasionally challenged? Instead of always asking a client to perform a plank, for instance, in exactly the same way with the same words, wouldn’t the client benefit from experiencing the plank differently, based on where the attention is drawn and what words are used? Playing with the cueing of the shoulder girdle and shifting the perspective from back to front, or from finding stability through external rotation or adduction can change the entire sense of the exercise. We believe it is beneficial to have multiple degrees of freedom at a joint; this gives us several ways to accomplish a task if, for some reason, our favorite way to accomplish the task isn’t an option currently. Changing cueing and perspective offers multiple ways to experience an exercise, not through increasing range of motion, but by increasing internal awareness. And increasing internal awareness might be a good thing.

Yours in health and wellness,
Jenn
*Video link: https://www.youtube.com/watch?v=V4DyNgXsLKg

References:
Ludewig, P.M., Behrens, S.A., Meyer, S.M., Spoden, S.M., & Wilson, L.A., (2004). Three dimensional clavicular motion during arm elevation: reliability and descriptive data. Journal of Orthopedic & Sport Physical Therapy, 34(3), 140-149.
Frank, R.M., Ramirez, J., Chalmers, P.N., McCormick, F.M., & Romeo, A.A., (2013). Scapulothoracic anatomy and snapping scapula syndome. Anatomy Research Internation, doi: http://dx.doi.org/10.1155/2013/635628
Saccomanno, M.F.,  Ieso, C.D., & Milano, G., (2014). Acromioclavicular joint instability: anatomy, biomechanics, and evaluation. Joint, 2(2), 87-92.
Jurik, A.G., & Sorensen, F.B., (2007). Imaging of the Sternocostoclavicular Region. Springer: Denmark.
Berthoz, A., (1997). The Brain’s Sense of Movement. Harvard: Cambridge.