- Ab Machine Crunches | Ab Workouts - Another fantastic workout for your abs. Using an ab machine you isolate the abs for a targeted workout. Depending on your fitness level you can adjust the weight on the machine to increase the intensity of the workout. br br Even though free weight and body weight ab exercises work additional muscle groups besides your abs the ab machine is a great addition to your ab workouts. It provides a little variety so you don't get bored with the same old exercises every workout session.