Ball Sit

How to Do It: Sit on a large stability ball, with your arms straight out in a T, feet flat on the floor, abdominals engaged, and spine tall. Lift your right knee, letting your right foot dangle an inch or two off the floor. Build up to holding this position for 20 to 30 seconds, trying not to wobble while you maintain the pose. Switch legs and repeat for one set. Do two sets total.

What It Does: As you remove one point of contact with the floor, your body has to work to keep the ball from rolling around underneath you, which strengthens your core.

Make It Harder: Do the move as above, but lift your arms straight overhead in line with your body, palms facing forward. Hold for 20 to 30 seconds. Rest, then repeat for one set. Do two sets total.