Sit on the floor with legs spread (wider is easier, narrow is difficult). Lace your fingers behind your head, and keep your back straight. Tip to the right, allowing your right elbow to touch the floor. Keep those elbows drawn back. Straighten your back and tip to the left. Back and forth. Do three sets of 12 to 15 repetitions.

Popularity: 24% [?]

Sit on the edge of a bench, grasping on the sides of the bench with your hands to maintain steady balance. With your legs extended outward, slowly pull your knees into your chest, squeezing the abdominal muscles during the contraction. Hold this position for two seconds and then slowly extend your legs before repeating the motion. Try to keep from rocking and bouncing. Do 3 sets of 25 reps for this exercise

Popularity: 20% [?]

Lie on your back. Put your hands beneath your buttocks and bend both knees up to your chest. Extend one leg straight up towards the ceiling. As you bend it with a pedaling motion, extend the other. Repeat up to 20 times. Do not attempt this exercise if you suffer from back pain.

Popularity: 23% [?]