Here is is!!
I love incorporating the punches into an ab workout. First of all because they are fun and I don't have to be on the floor for a while. Second, doing cardio right after you pump up one specific muscle, causes your body to burn fat in that area like an inferno! The worked up muscle is like a space heater, concentrating your calorie burning efforts to that area. And last, because if you maintain proper form, you will be engaging your abs while punching. Twist at the waist and throw your left fist to right side and your right fist to your left side.
Notice there is not a number of times to repeat. You know what is challenging for your own body. But go past where you think you need to stop.