Get into a press-up position, legs extended with your feet and shins resting on a Swiss ball. Your hands should be directly underneath your shoulders.

Once you're balanced, slowly draw your knees in and to the right. The ball should roll towards you. Don't curl your head under to look at the ball. Your neck should stay in line with your back throughout the exercise. Hold, then extend your legs back to the starting position. Repeat, curling your knees up and to the left. Continue for as many repetitions as you can.