There's some serious juvenile novelty to this balance-testing move, which is scarier looking than it actually is to do. Your abs and lower back are the main targets here, but your core will benefit, too.
- Take an exercise ball and lie on top of it with your shins on the ball and your palms on the floor under your shoulders.
- Now use your abs and legs, rolling the ball to your middle, lifting your hips and keeping your head down between your arms. (Your body should be in an inverted "V" shape.)
- Hold here for 1 count and then roll back to the start.
- Do 10-12 reps. Be sure to pull your abs in and keep your head even with your spine as you move in and out of the "V".