Attach a resistance band to a door anchor. Place the door anchor on a door and adjust the height. Attach a handle to the other end of the resistance band. Stand side-on to the door, grab a handle with far arm. Keep elbow against side with elbow bent approximately 90°.
Pull the handle away from body by externally rotating shoulder until the resistance band almost touches abdomen. Return and repeat. Turn around 180° and continue with the opposite arm.
Maintain the elbow against side and fixed the elbow position throughout exercise.