But much more intense exercise, such as intervals, can lead to after-exercise higher metabolism for at least several hours. I don't think that's true of lower-intensity. Also, it doesn't really matter what you burn (fat or carbs). The main point is to burn calories, so again the higher intensity shorter workout does fine. Also also, I believe there is some evidence that longer low-intensity workouts are catabolic, that is that they can lead your body to eat into muscle more than shorter more intense workouts (this hardly proves it, but look at sprinters vs long-distance runners for body composition). Finally, the nutrients you use depend on the macronutrient balance in your diet, as I understand it. If you are on a low-carb diet, for example, your body can get the energy from fat. So, I wonder whether those results in those graphs are invariant to the sort of food they're eating, particularly the macronutrient balance.