Hook a rope attachment to one end of a cable crossover machine and an ankle strap to the other, and load 5 to 15 pounds on each weight stack. Set the pulleys to their lowest position. Wrap the strap around ankles and lie faceup between the pulleys, holding an end of the rope in each hand. Extend arms over chest and raise legs a few inches off the floor.
Pull knees toward chest as you crunch up, lifting shoulders off floor. Return to starting position. (If this is too challenging, keep knees bent the entire time.)