How to: From a kneeling position, place 2 arms with palms facing one another and thumbs up, shoulder width apart on a stability ball (55, 65, 75cm ball depending on size). Keep arms straight and locked out at the elbow. Slowly begin to round your spine (similar to a cat stretching). Gently drop your head, keeping the ball stationary or minimally rolling it away. Be sure to have a deep full breathe at the top. This can be done actively for reps of 3 seconds or held statically for 30+ seconds.
Compensations: Watch for bending of elbows and rolling the ball towards you.