Trunk rotation control on stability ball - dumbbells to side

Sit on a stability ball and hold a dumbbell in each hand.
Roll backward on the ball until it is behind your mid-back.
Position your feet hip-width apart on the floor and straighten your hips.
Raise the dumbbells towards the ceiling.
This is your starting position.
Quickly drop both dumbbells to one side, while maintaining your balance.
Slowly return to the starting position and repeat on the opposite side.