Jason Todd

Ever wonder why you still don't have a 6-pack after doing endless crunches? The crunch, although effective if performed correctly, mostly targets the upper abs.

In other words, you're missing obliques, lower abs, and other muscles that can shrink your middle and define your tummy. What's more, if you do crunches incorrectly you can end up with back pain, a stiff neck, and minimal results.

Why not try this Move of the Week instead? The Leg Drop is better at reaching those lower ab muscles, and when you hold a large stability ball between your legs it engages your inner thighs as well.

Be careful not to lower your legs so far that you arch your lower back, as this can cause back pain. Also make sure to engage your stomach muscles as you raise your legs to the starting position (straight up in the air)--don't use momentum to get it done.

To make this move even tougher, link fingers behind your head, elbows out, and curl up until your shoulder blades are off the floor. Hold this position as you move legs down and up.

Try this move: Leg Drop

What to do: Lie on your back with arms at the sides, palms down, legs long with a stability ball between lower legs. Engage abs and lift legs, bringing ball directly over hips. Keeping lower back pressed firmly into the floor, slowly lower legs toward the ground (try not to let them touch floor). Do 3 sets of 15 reps.