We tend to think that the routine that we do like writing, eating, playing an instrument, etc. are the work of our hands alone. But the truth of the matter is that without the shoulder, the mobility of our hands is limited, the arms would just fall limply on our sides. Even the simple motion of reaching your hand to your mouth would be quite impossible. This is why we should maintain the condition of these body parts through exercise, particularly yoga.
Reflecting on the significance of the shoulders, it is startling to note that they are somewhat vulnerable & unstable joints. Like the pelvis, the shoulder is a joint composed of a ball and socket. But unlike the pelvic joint, the socket on the shoulder is relatively not as deep. The reason for this is for mobility, allowing your arm freedom of movement. With it you can reach your arm in any direction 360 degrees. These kind of movements are impossible to make with your legs.
This innate unstableness makes the shoulder dependent on connective tissues to keep the link together. These soft tissues are composed of tendons, which connect bones to muscles; ligaments, which attach bones to other bones; and muscles, which keep the bones stable and produce movement. There are four muscles that keep the shoulder together and this group is referred to as the rotator cuff. They are wrapped around the joint producing movement every which way.
The rotator cuff is made up of the Supraspinatus, the Subscapularis, the Infraspinatus, and the Teres Minor. Aside from keeping the ball of the humerus within the socket of the scapula, each of the muscles are in charge of a particular arm movement. The shoulder is also braced by the clavicle.
The Supraspinatus muscle keeps the head (ball) of the humerus from sliding off partially out of the socket. This painful condition is referred to as subluxation which happens when the supraspinatus is under paralysis due to a stroke.
The Tadasana or Mountain Pose, which is standing with the arms to the sides then lifting the arms parallel to the ground, Virabhadrasana II or Warrior Pose II, strengthens the Supraspinatus. If you stand in the Tasadana position, then with palms toward your body turn the creases of your elbow forward, this rotates your shoulder outwardly strengthening the Infraspinatus & the Teres Minor.
These are some of the yoga positions that will help strengthen the shoulder preventing possible injury.