Crunch (on stability ball)

Sit on the stability ball with your feet flat on the ground and your knees bent at a 90-degree angle. Lie back on the ball until your lower back is supported and your upper body is parallel to the floor. Place your hands behind your head or across your chest. Engage your abs and lift your upper body towards your knees, curling your torso forward. Pause for a moment at the top of the movement, then slowly lower your upper body back down to the starting position. Repeat for the desired number of repetitions.