Works: obliques Lie faceup on ball, knees bent, arms extended above head. Crunch up as you pull an imaginary rope with right arm (as shown), then left arm. Continue until you're sitting. Reverse movement to return to start for 1 rep. Do 12 reps.
The Flat-Abs-Fast Secret: Lie faceup with hands behind head, elbows out, ball between feet, legs extended above floor. Lift left shoulder and crunch right knee to left elbow (as shown). Return to start; repeat on opposite side for 1 rep. Do 12 reps.
Works: abs, lower back Sit on ball and lean back with hands on floor behind you, palms down and turned out, legs extended. Bring right knee toward chest (as shown); return to start. Repeat with left knee for 1 rep. Do 12 reps.