Lie on your back with your arms out to the sides, palms down, and lift your legs with your knees bent at 90 degrees, stacked over your hips. Keeping your knees together, lower them toward one side - halfway to the floor is the target - then pull them back up to center and lower to the other side. Your shoulders and palms stay pinned to the floor throughout; the rotation happens through your waist, and your abs control every degree of it.

Works: obliques, abs, lower back

Breathing: Exhale as you pull the knees back up to center, inhale as you lower them to the side.

Common Mistakes: Letting the opposite shoulder peel off the floor as the knees drop, dropping the legs with gravity instead of lowering them under control, and letting the knees drift apart mid-rep.

Make Easier: Shrink the range - lower the knees just a quarter of the way - or pause at center between sides to reset. You can also start with Twists to groove the rotation.

Make Harder: Lower the knees further toward the floor while keeping both shoulders down, or straighten the legs and move on to Windshield Wipers.