Thawing a Frozen Shoulder
Before you begin stretching, it's a good idea to warm up your body, and your shoulder muscles in particular. Bearing light weight on the arms will not only warm up your shoulders but will also begin some strengthening. What's more, the isometric strengthening (the muscle is working but not changing length) in yoga poses is ideal.
Start with the easiest position, which is on hands and knees. Then lift each arm forward and up a little off the floor, one arm at a time. Just make sure that you keep lifting your torso up out of your shoulders so there's no valley between the shoulder blades. If you can be on hands and knees and lift each arm without pain, you're ready to progress to transitions from Downward-Facing Dog to Plank Pose and back. Though you (or your student) may be apprehensive about trying this, most frozen shoulders actually like mild weight bearing, especially if you do an easier variation, such as Downward-Facing Dog with hands on a chair seat.
Stretches to Restore Motion
With the muscles warm and lightly worked, it's a good time to do some stretching to restore the shoulder's lost range of motion. A typical frozen shoulder can only flex (bring the arm forward and up) to just above horizontal, and abduct (bring the arm out to the side and up) to just below horizontal. Normal range allows the arm to come all the way up to the ear in flexion or abduction. To restore the normal range, you must work carefully, with patience and persistence: Remember, pushing into pain is likely to generate muscle guarding at the time, and a more inflamed, painful shoulder afterward. Will you want to come back tomorrow and do these same stretches again when your shoulder is still very sore from the day before? Probably not, so do your stretches in a comfortable position, lying on your back on the floor. Support your arm in a position where you feel the stretch bordering on mild discomfort, but you can still breathe and relax into the stretch. Learning to relax the shoulder muscles in an open, lengthened position helps your body unlearn the guarding, tightening response that automatically accompanies pain.
While lying on your back, improve shoulder flexion by first stretching your arm up toward the ceiling with the shoulder externally rotated (if both arms are stretching up, the palms should be facing each other). If the shoulder is very sore and tender, use the other hand to help lift the weight of the arm and stretch it up. Then gradually take the arm over your head and toward the floor on the other side, thumb pointing down. When you reach the point of stretch with mild discomfort, stop. Have a friend or helper bring a prop (whether it's a chair seat, block, or folded blanket) to support the arm at just that height. Then at that point of stretch, but not pain, let go of the weight of the arm so the prop supports it fully. Breathe and relax for two minutes or more. Do this stretch at least once a day.
To improve abduction, open your arms out to the sides with palms up, while still lying on your back. Again, use support for the arm at just the right point of stretch sensation. When the arm is at about 90 degrees of abduction, you can also work on external rotation of the shoulder by bending the elbows to 90 degrees and releasing the forearm and back of the hand toward the floor behind you, with the palm up (the hand will be at the same level as your ear). Because this is usually the most difficult movement to restore, use plenty of height in your supporting props, and plan on slow progress.