The Target: Your abs, lower back and hips
Assume a push-up position. Your body should form a straight line from your head to your ankles. Tighten your core by trying to make your stomach as skinny as possible, and hold that contraction for the entire exercise [A]. Keeping your arms straight and your body rigid, shift your weight onto your left arm and rotate your torso up and to the right until you're facing sideways. (Pretend you're reaching upward.) Pause for three seconds, then lower back down the starting position, rotate all the way to your right and hold again. Continue to rotate back and forth.
Next, try the Swimsuit-Ready Workout