Scapular retraction/protraction side lying stability ball with assistance

Lie on your good side and ask an assistant to help place your weaker arm on top of a ball.
Your arm should be a similar height off the floor to your shoulder.
Bring your shoulder blade back toward your spine.
Slowly roll the ball up toward your head, whilst the assistant helps to keep your arm and hand on the ball.
Remember to keep your shoulder blade still.
Slowly roll the ball back to the starting position.