PREPARATION
1.Lie on your back, with your
  knees bent and feet flat on the
  floor.

2.Place your hands behind your
  head, elbows out to the side. 

3.Cross your right foot over your
  left knee. Breathe in.

EXERCISE
1.Breathe out as you raise your
  left shoulder toward your right
  knee. Keep your right elbow on
  the floor.

2.Hold briefly, then breathe in as
  you lower your shoulder back to
  the floor. Do not relax your
  abdominals between reps.

MAINLY FOR: External obliques