SETUP: Lie flat on the floor with your arms out for support. Raise both legs to a 90* angle, keeping feet together and a slight bend at the knee.
REP: Keep your abs tight and lower your legs to one side in an arc-like motion, getting as close to the ground as you can without losing form. Squeeze your obliques to pull your legs back in that arc-like motion until they’re dead center again. Now do the same thing to the opposite side.
TIP: There should always be a slight pause when you return to center, this prevents momentum from creeping in and makes the exercise 100x better.