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

2.Place your hands behind your
  head.

3.Tilt your pelvis forward, so
  your lower back is pressed
  against the floor. Breathe in.

EXERCISE
1.Breathe out as you raise your
  right shoulder and left foot.
  Twist at the waist, drawing your
  right elbow and left knee
  together.

2.Breathe in as you lower your
  shoulder and foot back to the
  floor.

Try not to relax your abdominals
between repetitions.

MAINLY FOR: External obliques