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I usually stick to HIIT because of the "hamster on a wheel" thing. That and it burns a hell of a lot of calories if the intensity is high enough.
Doesn't running or sprinting on whatever increase mitochondrial density which then spares muscle glycogen and uses more lipids instead? So maybe that somehow contributes to the overall calorie burn?
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Depends on how hard and how long you go. Anaerobic exercise like sprinting is going to primarily use anaerobic energy systems (i.e., ATP and glycolytic). This is going to run your ATP & CP stores down and start to call on your glycolytic energy system to break down glycogen. Once you breakdown enough glycogen though, you will exceed your lactate threshold and will be forced to decrease intensity and use your aerobic energy systems, thus metabolizing carbs, fat, and protein for energy. I think this is why ABC's authors state that they think a combo of HIIT and steady state cardio may be best for fat loss.
Its my opinion though, that hitting the cardio quick, hard, and often will keep your EPOC high and burn more calories. When you break it down, its calories in vs. calories out, when proper nutrition and training are considered. I intend to do more writing in the near future after releasing Part 2 of EPOC-alypse (the writing is down, I just need to type it when i get home) about energy flux or "G flux" that encourages increased calories and activity to keep your metabolism at its absolute peak.