Start lying on your back with both legs extended toward the ceiling, pressing your lower back into the floor. Rest your arms on the floor next to your body. Cross your left ankle over your right.
Using your lower abs, raise your hips a few inches off the floor, then immediately lower them with control. Keep your feet directly above your hips. That's one rep.
Do eight reps. Then cross your ankles with the right foot on top, and do eight more.
Jenny Sugar is a former PS staff writer. She reports on all things fitness, but especially loves CrossFit and yoga.