Resisted external rotation on a stability ball (Shoulder external rotation strengthening, with band (bilateral), arms at sides, sitting on stability ball)

Sit on a stability ball with both feet firmly on the floor.
Hold a resistance band between both hands.
Find your neutral sitting posture and hold this position.
Bend your elbows to ninety degrees.
Keep your elbows by your side as you pull your hands away from each other to make the band taught.
Control the movement as you bring your hands back to the starting position.