Understanding shoulder function and the structures that stabilize and produce movement can make a huge difference in your yoga practice.
In part one of Yoga and Shoulders: It’s A Scapular Matter, we learned how the shoulder is comprised of four joints, the glenohumeral, acromioclavicular, sternoclavicular, and scapulothoracic joint.
In this next installment, we will learn about the supportive structures that stabilize and protect the shoulder joint at a deeper level.
About the supportive structures
1. Glenoid labrum
The glenoid labrum is a thick cartilaginous structure apart of the shoulder blade that supports the head of the arm bone inside the socket.
It deepens the socket and helps keep the humeral head stable in the socket. The labrum acts as a suction cup to hold the humerus in place to avoid dislocation. Injury to the glenoid labrum may gradually develop with repetitive overhead motion.
When you try to catch yourself during a fall or lift a heavy object, traumatic injury can occur to this supportive structure.
The shoulder has a large number of fluid filled sacs called bursae. There are three major bursae known as the subacromial, subdeltoid, and subscapular bursa.
Serving to provide cushioning and lubrication to the shoulder joint, you can think of them as tiny water balloons that slide around to reduce compression and sheering to the soft tissues around the joint.
3. Glenohumeral ligaments
There are three ligaments that make up the glenohumeral ligaments—superior, middle, and inferior. This group of connective tissue serves to provide protection and stability to the front portion of the shoulder joint.
The superior glenohumeral ligament joins together with the coracohumeral (cor-a-co-hu-mer-al) ligament to stabilize the head of the humerus, however, the greatest stabilizer of the three is the posterior glenohumeral ligament.
The four main muscles
There are four main muscles that help to stabilize and assist with movement in the shoulder. These are known as the SITS muscles or rotator cuff.
These muscles help to stabilize the shoulder joint, while the primary mover muscles create the power to produce the movement of the arm. And without these muscles, the head of the humerus would dislocate or slide around in the joint, resulting in little stability and fixation for precise movement.
The SITS muscles include:
- Teres minor
How the SITS muscles work
This muscle is found on the top of the shoulder and follows under the upper traps out to the head of the humerus (upper arm bone). It assists the deltoid or primary mover within the first 30 degrees of shoulder abduction and continues to stay contracted throughout the movement to provide stability in the joint.
It is the most commonly injured muscle in the shoulder and can be easily injured from constant overhead activities. These injuries may result in inflammation and pain, eventually leading to sheering or fraying of the tissues, until finally rupturing completely.
2. Infraspinatus/Teres minor
These muscles assist in external rotation and adduction of the shoulder. They are also essential when attempting Tall Mountain pose or Downward-Facing Dog as they help you to reach above and behind your body.
The infraspinatus is located on top of the shoulder blade and attaches to the backside of the humeral head (arm bone).
Teres minor is located on the upper lateral border of the shoulder blade and attaches to the backside of the humeral head. This muscle is also wedged between the infraspinatus and teres major.
This muscle is located on the inside of the shoulder blade, maintaining the shoulder blade directly on the thorax (rib cage).
Subscapularis allows us to bind ourselves in yoga postures. Weakness of this muscle can result in winging of the scapula, which is where the shoulder blade protrudes off of the back instead of laying flat against the back of the thorax.
Winging is a common dysfunction of the shoulder girdle and is typically associated with poor posture. You will notice this dysfunction when paying close attention to a student’s shoulder blades in Chaturanga Dandasana.
In a healthy shoulder girdle, the shoulder blades will stay on the back and glide along the rib cage. However, in a shoulder girdle with dyskinesia (dysfunction of movement) the shoulder blade will lift off the rib cage and present a wing-like movement.
Every joint, connective tissue, and muscle of the shoulder structure has to move in accordance with one another to create fluidity, strength, and precision.
If there is any dyskinesia present, you could find yourself at risk for shoulder injuries during your yoga practice. This can result in sheering connective tissues, building toward an impingement, or a rotator cuff tear.
Stay tuned for the next installment of Yoga and Shoulders: It’s a Scapular Matter, where we will discuss the muscles that refine our movement and muscular intelligence including primary movers, fixators, and synergists.