Chris ShipmanFrom Health magazine
1. Lie on your back with your hands behind your head, elbows wide, and knees bent to a tabletop position, with your heels together and toes turned out.
2. Press your legs up and out, keeping your heels and toes in the same position and squeezing your inner thighs as you crunch your head up off the floor. Be careful not to strain your neck by pulling on the back of your head with your hands. Bend knees back into the starting position, and lower your head to the floor (or you can keep it lifted the entire time for a more advanced move) to complete 1 rep.
Do 8–10 reps a week, and your tummy should be trimmer in just 3 weeks.