Trunk flexion (stability ball) ("Child's pose" Shoulder/trunk extensors stretch, sitting behind stability ball)

Sit upright on a firm surface or chair with your feet slightly wider than hip width apart.
Place a stability ball on the floor in front of you so that it sits between your knees.
Place your hands on top of the ball and slowly roll it forwards.
As you roll the ball forward, bend through your back and look down towards the floor.
Roll the ball back towards you as you return to sitting up tall.