The weighted Swiss ball crunch increases strength and stability of the core and obliques while also improving balance.
Lie back on a Swiss ball with knees bent at a 90-degree angle and feet on the floor about shoulder-width apart. The ball should be under your hips and lower back. Hold a dumbbell to your chest. This is your starting position.
Crunch your torso toward your knees, raising your chest upward. Stop when the middle of your back loses contact with the ball. Pause, then return to starting position.
Avoid pulling on the back of the head.
Avoid sitting too low on the ball. Your abs should be stretched in the down position and fully contracted at the top.