Does your training zone determine the fiber type used? Does fiber type determine aerobic or anaerobic pathways, carbs or fats? We answer these questions by looking at evidence and concepts that show that fast twitch fibers can be just as aerobically capable as slow twitch fibers, nearly as good at burning fats, and why that might be. We dissect a paper on elite cross-country skiers, and another paper on whether or not fast twitch fibers had been recruited at relatively low intensity. In-depth discussion follows on fiber type distribution, muscle mass recruitment and force availability, why endurance athletes defy the expected metabolic properties of fast twitch fibers, and why these expectations may have started with cats.