A challenging way to intensify your abdominal work is to perform a reverse curl with an oblique crossover curl. This will engage the sides and lower section of your abdominals in one move. If you have tight hamstrings, you can modify this move by bending your knees.
Lie face-up on a padded surface or mat. Place your hands behind your head with elbows pointed outward. Raise your legs in a straight or bent position, making sure that your knees are directly over your hips. On an exhalation, contract your abdominals and raise your head, shoulders and chest off the floor. Pause for two breaths, then release your upper body to the floor.
Perform this move again, but this time press the palms of your hands together while keeping your elbows straight. On the exhalation, rotate your left shoulder to the right and reach your arms to the outside of your right thigh when you contract up. Pause in the air, keeping your hips square to the ceiling and your left shoulder raised off the floor as high as possible. Hold for three breaths. Lower your upper body to the floor and repeat on the other side.
Voight is the creator of a line of fitness DVDs, including "Full Body Stretch" and "Ballet BodySculpt."