Works: obliques, trunk, abductors (outside of hip), and shoulders
Lie on your side with your elbow directly under your shoulder. Keeping both feet flexed, use your obliques to lift your hips- don't arch your back! Lift your right leg and crunch it in. Extend your leg back out for one rep, then lower it. Repeat 10 times, then switch to left leg.
Source: Equinox South Beach