30-Minute Abs: Week 3, Workout IX
Sets: 3-4 Reps: 10-15 Rest: 90 Seconds
Hold a medicine ball straight overhead and stand with feet staggered . Throw the ball straight down into the floor as hard as you can  and catch it on the rebound. That's one rep. Switch the leg that's forward on each set. Do not allow your speed to hurt your form.