Perform Moves One and Two on right leg, and, without resting, add Move Three: Bring the right knee in toward the chest no further than your elbows. Hold for one second—your abs will feel it. Then fully extend the leg back out to the starting position. Do this 20 times, followed by six push-ups with leg raised, as before. Rest for 20 seconds. Switch legs and repeat Moves One, Two, and Three. (That's one set.) Do the whole circuit again for a second set. Rest for 20 seconds with both knees on the floor.