Sarah is a former collegiate swimmer with a history of left…

Sarah is a former collegiate swimmer with a history of left shoulder pain.  To this point, your primary focus of treatment has been strengthening the rotator cuff to improve the dynamic stability of the glenohumeral joint. In the most recent visit, you choose to strengthen the rotator cuff by performing humerothoracic external rotation in standing using resistive tubing (see picture).  However, you quickly notice the medial border of Sarah’s scapula becomes prominent (i.e. scapulothoracic internal rotation or “winging”) when she is moving into humerothoracic external rotation.  What could be causing this and how would you modify the exercise to avoid it?