Prone trunk extensions over stability ball (Trunk extension/scapular retraction strengthening, arms 90/90, prone over stability ball (level 1))

Lie on your front bent over a stability ball.
Stabilise your feet on the floor.
You may find this exercise easier to perform by putting your feet up against a wall.
Hold your hands by the side of your head.
Lift your chest upwards and extend your body on the stability ball, drawing your shoulder blades and elbows back. Return to the start position in a controlled manner and then repeat.