In this exercise, the rear-most shoulder muscle (posterior deltoideus or ‘rear delt’), and the muscles that pull the shoulder blade in towards the spine (rhomboideus or ‘rhomboid’) are effectively stretched. Together with thoracic flexion movements, this exercise will stretch in between the shoulders, a place where many hold tension.
Once held, use the arm, shoulder and back muscles of the catching arm to draw the arm onto the front of your neck; if you bring the arm onto the chest there may be no stretch at all. Pull the held shoulder down in the direction of the waist, using the big muscle under the arm (latissimus dorsi) to intensify the stretch, as we find that most people tend to shrug the shoulder while doing the exercise. If you can, you may hold the back of your neck as a way of holding the stretch for a while without much effort (photographs 2 and 4).
The contraction is to press the held arm straight away from you gently for a few seconds. Stop pressing, relax and breathe in deeply. On a breath out, increase the stretch by pulling the arm closer to the front of the neck and keep the shoulder held down. Hold for four or five breaths in and out and repeat for the other side.You should feel the effect at the back of the shoulder, and perhaps across the back, and you may feel a small compression sensation in the front of the joint itself.
You can move the effects around to an extent, by letting the upper back slump, or by laterally flexing the spine; to this you can try adding a small rotation of the upper body to both sides. Adding these secondary movements can change the focus of the stretch considerably, and may just find that particular place you need to stretch.