The shoulders are one of the most mobile areas of the human body. This makes them both incredibly useful and simultaneously high-risk in terms of pain and tightness. Luckily, yoga asana practice can provide some solutions.
A quick note on anatomy
Since many important shoulder muscles are actually quite difficult to differentiate and isolate, it will be helpful to quickly discuss how stretching works. On a very simple level, when we stretch we're lengthening the muscle being stretched, while contracting (shortening) the antagonist muscle. This means that we’re contracting the muscle that performs the action opposite of the one we’re working on.
This is the case for most muscles in the human body (with the potential exception of the external rotators in the hip which we stretch by finding external rotation and flexion simultaneously). For example, if we’re stretching the hamstrings (back of the leg), we’re contracting the quadriceps (thigh muscles).
Now of course gravity and external forces may also be pulling you deeper into a stretch, however safe and active stretching should involve this type of antagonist contraction.
Back to the shoulders
Because there is so much range of motion in the shoulder, we sometimes need to identify the muscles by their primary movements. This allows us to notice where we’re tight, and easily find the correct (antagonist) motion that we should perform to effectively stretch.
So, let's go through some of the main shoulder muscles and discuss different stretches for each. We’ll cover the muscles of the rotator cuff, which stabilize and move the glenohumeral joint (where the arm bone connects into the shoulder), and we'll cover the scapular stabilizers which position the shoulder blade on the back.
While there are other muscles that help with larger movements of the shoulder and arm, we’re choosing to cover the areas that are often difficult to identify and reach. However, once you get the logic of identifying antagonist movements, you’ll be able to effectively find stretches for any muscles that may be giving you trouble.
The Rotator Cuff
Infraspinatus and Teres Minor - The infraspinatus covers the bottom portion of the scapula below the shoulder blade’s bony ridge and connects to the back of the arm bone (humerus). Its main motion is to externally rotate the arm (rotate the arm so the bicep faces away from the body). Teres minor attaches at the bottom of the scapula and also extends to the back of the humerus. We discuss the infraspinatus with the teres minor muscle, because they both serve more or less the same function.
To stretch the infraspinatus and teres minor - Since the main motion of these two muscles is external rotation, we can stretch them by finding internal rotation. One of my favorite ways to do this is to move into Extended Side Angle pose, then bring the back of the bottom hand to the lower back and tuck the elbow of the same arm on the inside of the front bent knee [see picture]. Push elbow into knee and knee into elbow. Another option is finding Gomukhasana Arms, by reaching your right hand up to the sky, bending at the elbow and dropping your right palm to your mid back, then bringing your left hand up to clasp with the right. This creates internal rotation in the lower arm, which is the focus of this stretch.
Supraspinatus - The supraspinatus is a small muscle that runs across the top of the shoulder just above the bony ridge of the scapula. Its main purpose is to stabilize the head of the humerus, and to a lesser extent, lift the arm away from the body in its bottom range of motion.
To stretch the supraspinatus- Since the motion of the supraspinatus is lifting the arm away from the body (abduction), we want to find the opposite motion of pulling the arms in towards the midline (adduction). One good way to do this is to clasp the hands behind the low back with the fingers interlaced. Then, roll the shoulder blades back and down as your fists reach towards the floor and the chest shines up.