Superset: do the straight-leg crunch for 15-20 reps, then immediately go into 20 reps of bicycles. Rest 30 seconds between supersets, and aim to do 3-5 supersets total.
STRAIGHT-LEG CRUNCH (UPPER ABS) Start: Lie faceup on the floor with your legs extended in the air, perpendicular to your upper body. Extend your arms toward your feet. MOVEMENT: Contract your abs to lift your shoulders off the floor as you reach with your hands toward your feet. Reverse the motion, but don’t return all the way to the floor; stop just short and begin your next rep.
BICYCLE (LOWER ABS AND OBLIQUES) Start: Lie faceup on the floor with your knees bent and feet flat on the floor. Place your hands lightly behind your head. MOVEMENT: Simultaneously crunch up and cross your right shoulder toward your left knee while pulling that knee in toward your chest. Alternate from side to side; once to each side equals one rep.