Shoulder external rotation stretch (assisted) (Shoulder internal rotators stretch, with assist, arm bent at side, sitting)

Sit upright in a chair with an assistant sitting to your side.
Ask your assistant to take your arm, with one hand under your elbow and the other at your wrist.
Bend your elbow to 90 degrees and ask your assistant to slowly turn your forearm outward, keeping your elbow close to your body.
When you feel a point of stretch, hold this position, avoiding stretching into pain.