Lie on your back with your heels resting on a stability ball hip-width apart.
Loop a resistance band around your hands under moderate tension and rest your hands on your lap.
Simultaneously press your heels against the ball and lift your hips up whilst you raise your hands overhead, maintaining tension on the band.
Try to straighten your hips so that you have a straight line from your shoulders to your feet.
In a controlled manner lower your hips and arms back down.
Repeat.