1. Bicycle Maneuver: Lie flat on the floor with your lower back pressed to the ground. Put your hands beside your head. Bring your knees up to about 45-degree angle and slowly go through a bicycle pedal motion. Touch your left elbow to your right knee, then your right elbow to your left knee. Keep even, relaxed breathing throughout.

2. Captain's Chair: Stabilize your upper body by gripping the handles and lightly pressing your lower back against the back pad. The starting position begins with you holding your body up with legs dangling below. Now slowly lift your knees in toward your chest. The motion should be controlled and deliberate as you bring the knees up and return them back to the starting position.

3. Crunch on Exercise Ball: Sit on the ball with your feet flat on the floor. Let the ball roll back slowly. Now lie back on the ball until your thighs and torso are parallel with the floor. Cross your arms over your chest and slightly tuck your chin in toward your chest. Contract your abdominals, raising your torso to no more than 45 degrees. For better balance, spread your feet wider apart. To challenge the obliques, make the exercise less stable by moving your feet closer together. Exhale as you contract; inhale as you return to the starting position.

4. Vertical Leg Crunch: Lie flat on the floor with your lower back pressed to the ground. Put your hands behind your head for support. Extend your legs straight up in the air, crossed at the ankles with a slight bend in the knee. Contract your abdominal muscles by lifting your torso toward your knees. Make sure to keep your chin off your chest with each contraction. Exhale as you contract upward; inhale as you return to the starting position.

5. Reverse Crunch: Lie flat on the floor with your lower back pressed to the ground. Put your hands beside your head or extend them out flat to your sides-whatever feels most comfortable. Crossing your feet at the ankles, lift your feet off the ground to the point where your knees create a 90-degree angle. Once in this position, press your lower back on the floor as you contract your abdominal muscles. Your hips will slightly rotate and your legs will reach toward the ceiling with each contraction. Exhale as you contract; inhale as you return to the starting position.

Because the hip flexor muscles work during ab exercises (which might take a way from the work of the abs), the researchers measured that, too, and found that the exercise ball, even though it did not generate the most activity in the rectus abdominis and obliques, did generate significantly less activity in the hip flexor. They reported that because of this, the exercise ball may be the best overall ab exercise of the exercises studied.