This one is great for your obliques, your little inner corsette. Lie on your back with your legs up, bottoms of your feet toward the ceiling. Keep your arms straight out in line with your shoulders with your palms against the floor to stabilize your upper body. Squeeze your glutes to tuck your tailbone and engage your core before you begin. Slowly lower down toward one side, keep your feet together the whole time. Use your core to pull your legs back up to the starting position. Repeat on other side.