Alright, its my understanding that the body does the following things in this order when performing cardio:
1. Burns energy you've obtained from food
2. When food has been burnt, fat stores beging to get burnt off
3. Muscle stores start to get burnt
Now I can understand why its best to workout on an empty stomach because you skip #1 and jump right to #2, but whats stopping your body from burning fat and burning muscle simutaneously and if #1, #2, and #3 above are in the correct order, what tells the body to go to #2 before #3 and what tells it when its time to switch.
Hope that wasn't too confusing