Borghe, I don't agree with your 30-40 minute thing. One, because depleting glycogen stores takes about 90 minutes, and two because it's irrelevant except in terms of increasing total caloric burn.
When you exercise for any kind of cardio activity, you'll burn both glycogen and fat. The actual percentages differ based on intensity (HIIT is most effective per unit of time), but it's irrelevant again.
Say you theoretically use 100% glycogen for your run. No fat was burned during the run. During the rest of the day, caloric intake is pushed to glycogen and the energy requirements of your body come from fat stores.
Say you use 100% fat for your run. Caloric intake will not be used to refill glycogen, and instead will be pushed to fat stores.
Do you see what I'm saying? Burning fat during your run is not important. Total caloric expenditure is 95% of the puzzle for running.
Then again for a variety of reasons focusing on running and cardio in general is a poor way to lose fat anyway. Cut calories and do resistance training, it's more effective.
When you exercise for any kind of cardio activity, you'll burn both glycogen and fat. The actual percentages differ based on intensity (HIIT is most effective per unit of time), but it's irrelevant again.
Say you theoretically use 100% glycogen for your run. No fat was burned during the run. During the rest of the day, caloric intake is pushed to glycogen and the energy requirements of your body come from fat stores.
Say you use 100% fat for your run. Caloric intake will not be used to refill glycogen, and instead will be pushed to fat stores.
Do you see what I'm saying? Burning fat during your run is not important. Total caloric expenditure is 95% of the puzzle for running.
Then again for a variety of reasons focusing on running and cardio in general is a poor way to lose fat anyway. Cut calories and do resistance training, it's more effective.