Not sure what the exercise is called, but if you have a friend who can assist, lie on the floor with your head between their feet. Grab on to their ankles and slowly raise you legs to their hands. Make sure your legs are straight and together. Have your friend push your legs down to the front, left and right, making sure that your ankles never hit the floor. Keep bringing your legs back up to their hands for about 100 reps.......that one really hurts me.