All three energy systems "happen" when you are doing exercise, that is fat burning, carb burning both aerobic and anaerobic. Which is doing "more" at any given time depends on intensity.

One of the reason the low intensity workouts or "fat burning" zones is actually useful for me and my clients, because it keeps then from feeling like failures. most studies have pretty much shown that if you have a short time to workout and do race pace type intensities, you can burn as many calories or even more than the lower intensities. BUT most people don't have the fitness for those hard workouts. So they might try on, and puke or feel horrible, and then quit. So thats when you introduce periodization, and working up to those types of workouts.

Don't worry about the number of calories from the total activity. the right workout is the one you will do. whether its running, or biking or a cardio class. the right time of day, again is the one that suits you. if you prefer mornings, great, afternoons are good too. no point in forcing yourself to do a workout and hate it. which will actually release more stress hormones and actualy prevent weight loss. your exercise shouldn't be work at all. it should be PLAY

Smile

han