I'm interested in the debate: cardio on an empty stomach in the morning VS cardio after a good breakfast.
Myself, I always do heavy cardio after I have had some food. It makes me feel stronger during the work out. When I do it on an empty stomach I tend to feel a bit weak.
My way of thinking is that after I have eaten, not only am I going to feel stronger (so mentally, the cardio session wont feel sluggish), but my body will more readily use calories as it is fully fueled up. If I do it on an empty stomach, then my body will be less likely to use calories. I'm specifically talking about the afterburn calorie usage here. I do HIIT, so the afterburn calorie usage is very important to me.