Let's start by doing a quick recap of our shoulder anatomy:
· The shoulder or glenohumeral joint is a ball and socket joint that involves the articulation between the head of the arm bone (humerus) and the glenoid fossa of shoulder blade (scapula)
· It is a shallow joint and has the greatest mobility of all joints in the body
· With this range of movement comes instability and a risk of dislocation
· The joint relies on a set of muscles called the Rotator Cuff muscles to provide stability
The Rotator Cuff muscles:
The Infraspinatus lies below the spine of the scapula and inserts on the greater tuberosity of the humerus. It works alongside Teres minor to produce external rotation. These are the only two muscles in the body that facilitate this movement.
The Supraspinatus lies above the spine of the scapula and also inserts on the greater tuberosity of the humerus. It initiates arm abduction and is the most frequent rotator cuff muscle to become injured due to impingement.
The Subscapularis lies beneath the scapula, inserts on the lesser tuberosity of the humeral head and is involved in internal rotation of the shoulder joint.
What is Shoulder Impingement?
The Supraspinatus travels through the shoulder joint and the current belief is that its tendon can become impinged (pinched) between the acromion process of the scapula and the greater tuberosity of the humerus.
There is a common belief in yoga teaching that in asana where we bear weight on the shoulder joint, like Chaturanga, by externally rotating the shoulder joint we create space within the joint and this will prevent shoulder impingement. This belief also therefore condemns internal rotation of the shoulder joint when weight bearing. However there is actually very little evidence to support this theory of shoulder impingement (reference below) or the correlation between pain and tissue damage in the shoulder.
In terms of relating this complex topic to our own yoga practice it is important to remember that we each have unique anatomy and while many of us may feel more spacious in our shoulder joints with a degree of external rotation, some of us may benefit from a degree of internal rotation. Explore this in your own body by standing with your arms by your side and raising your arms slowly above your head while externally rotating your arm bones. Then repeat this while internally rotating your arm bones. Notice which variation felt more spacious and allowed for more smooth, controlled movement. Then repeat this in a Child’s Pose position. How does adding some weight to the arms affect this?
Internal rotation of the shoulder joint is a natural movement that we must be able to perform adequately in order to keep the joint as healthy as possible.
Reference: Lewis JS. Subacromial impingement syndrome: a musculoskeletal condition or a clinical illusion? Physical Therapy Reviews 2011;16(5):388-398