And we're going to go down to the floor for crunch ... If you have more than one medicine ball, you might find that you want a lighter one for some exercises and a heavier one for others.

Let's start with a waist crunch. Have a seat on the exercise mat ... You can, for instance, hold onto a medicine ball -- or how about some weights as well? Again, you start with five repetitions ...

This makes ab workouts with a medicine ball more effective at burning calories and engaging your core than if you did the same workouts without one. There's no fitness baseline you need to work ...