Set up with a LAX ball or other small ball you can use for soft tissue work with a rack, post, or in a doorframe. Place the ball between the rack and your trapezius muscle at the top of your shoulder. Move your arm around, pinning the trap muscle and stretching it across the ball. Move the ball carefully to a few different spots on the muscle as you open up new spaces. Stay at or below a 3/10 level of discomfort so that your muscles relax into the movement.