The Shoulder Complex
Understanding the structure and function of our most mobile joint
The shoulder joint is a complex piece of hardware; it comprises of three very unique bones, the Humerus (Upper arm), the Clavicle (Collar bone) and the Scapula (Shoulder Blade). Additionally you could argue the rib cage is another vital part of the shoulder joint because without it the shoulder blade would not have a base of support to glide over while moving, or fix to while pushing and pulling heavy loads.
The second portion of the shoulder complex is between the humerus and scapula, the Glenohumeral Joint or GHJ. It is the combination of movement from the Scapulo-Throacic Joint or STJ and GHJ that allow the shoulder to be the most mobile joint in the body, however this inherent mobility comes at a trade off for stability, because the bones create a very shallow ball and socket it is the role of our soft tissues (muscles, tendons, ligaments and connective tissues) to provide the control and strength to the shoulder joint.
There are a number of ligaments and muscle tendons that cross and act on the joints of the shoulder. Four of the most famous, or infamous depending on how you come to read this article is the rotator cuff. Although they are muscles they act on the shoulder much more like ligaments. Originating from your Scapula they reach out in a spiral-like manner to grab the head of the humerus and pull it into the very shallow socket of the scapula, this motion by the rotator cuff is the act of centration or keeping the ball centred in the socket of the Gleno-Humeral Joint while the larger more powerful muscles move the upper arm and shoulder blade in its many planes of motion.
Muscle misuse and disuse due to life in the 21st Century
Have you ever been told you have bad posture, told to stand up straight, pull your shoulders back or stop hunching over? This is a common story, but why is it that so many people find themselves in this “bad posture” in the first place?
Posture is often looked at as a static or resting position that people fall into and where they spend a large portion of time, however human beings are not static creatures we are designed/evolved to move! Whether it’s the way we sit, stand or anything in between this is just a snapshot in time, the problem is never one single posture or position but our ability to move from one position to another fluidly, with strength and without pain. If you’re looking for the answer to bad posture it is just that, movement.
The human body is incredibly adaptive and will change and conform to the environment it is placed in. When we find ourselves being slightly hunched over or rounding our upper back, a position that is a frequent part of life in the 21st century from the time spent at our desk, looking down at our phones, behind the wheel, or even while reading this article – our body adapts by recognising this as our strongest and most comfortable position, the more time we spend there the more we will stay there. Unfortunately this is why just pulling your shoulders back and standing upright isn’t enough, because the moment you are no longer consciously thinking about your posture, you will fall back into your most comfortable and familiar position.
Muscles that act on the same joint must work together to balance the forces of creating movement, but when this balance breaks down through either misuse or disuse of a particular muscle group it will create a relative imbalance on the joint. One or more muscles acting on the joint will sit at a tight/shortened position while the other(s) a lengthened/weakened position this in turn affects the muscles’ ability to contract and relax effectively limiting our range of movement, increasing the risk of injury and potentially leading to pain in chronic overuse situations.
Imagine your muscles are like big meaty rubber bands, because they do in fact share a number of qualities when it comes to the way they function. Both muscles and rubber bands can “stretch” and also “recoil/contract”, but the key is the combination of the two, a rubber band left stretched is not very good at recoiling, much like a band that is only kept at its shortened position can stretch as well.
Returning strength and function through movement and exercise
Without the strength and “feeling of” stability provided by the muscles, our ligaments and joints would not make it through the day. The shoulder is acted upon by dozens of muscles, ligaments and connective tissues all working together playing their part to create, absorb and synchronise movements.
Almost all joints within our body operate using the Agonist – Antagonist relationship.The Agonist is the muscle(s) that contract to create movement while the Antagonist muscle(s) lengthen to allow the joint angle to change. It is the balance or push and pull relationship between the two that generate and absorb forces acting on the joints of the body. When this relationship breaks down and one muscle begins to dominate it can create problems. Many of the positions we sit and move into throughout our day dominate one side of this relationship and it is not necessarily a bad thing because to get a focused day of work done we need to lock in and focus on the task in front of us and posture rightly so becomes an afterthought.
The antidote to these resting postures is returning a balance to the body and this is achieved through training the muscles and joints to be mobile, flexible and strong in all positions and planes of motion. This is the case for anyone that finds themselves in a sustained position or repeating a particular task throughout their day, this can be in a workplace and/or a sport/skill based setting. For example, consider the conditions of swimmers shoulder, jumper’s knee, tennis or golfer’s elbow and the same problem arises due to this lack of balance at the joint due to a relative overuse of a particular muscle or muscle group.
As previously mentioned there is no such thing as a bad posture or movement, only our relationship with it, too much of anything can become detrimental much like not enough can lead to similar problems. The key concept to remember is misuse and disuse of movements and muscles get you into this and balanced movement will get you out.
Suffering with shoulder pain and need some help with your rehabilitation? Our Exercise Physiologists can help get you back to your best performaning self. Click here to book in your initial consult today!