That seems to make sense.
But it brings me to a similar question, since we are able to convert back and forth, carbs/fat/fat/carbs, it would seem like you would still be drawing from the total available. If you have your body in a run for 1 hour, you're body is going to have to find that fuel and use it. Hypothetically if it were 2-3 hours, that fuel would be burnt by physical requirements at the moment.
As far as I remember, HIIT's benefits for fat loss were that your body continues to burn at a higher rate for 10 hours or so after the workout. But not necessarily during the excersize? I'm mostly trying to figure out how to give these guys the most efficient workout I can. At the moment I don't think (this one) can crank out some good sprints without crashing and sliding along the ground.
I was thinking about the idea of "self selection." When I was young, 16-20 or so. I was just a lean kid. From that moment if I got into track and distance running, I would've developed into that build. Instead I boxed, and eventually developed the build of a fighter. If I were a sprinter, then I'd have that build. I agree though, that I never could've trained my way to be a 7 foot tall center, or a 250 pound sumo. But I could reasonably be a very lean runner, or at some other polar end of my genetic range.