Extend your right leg out to the side and your right arm up in the air. Balancing on your left leg, squeeze your abs in tight and pull your right knee and right elbow together doing an oblique crunch. Repeat the crunch twice, and for the third crunch extend the arm and the leg making a longer lever. The rhythm of this movement should be: 1) knee to elbow, 2) knee to elbow, 3) long arm long leg.
Repeat this 1,2,3 sequence 10-15 times. Repeat on the left side.