Quote Originally Posted by tulip View Post
To burn fat and lose weight, I understand that it's best to do sustained aerobic workouts in which your heartrate is between 60% and 80% of max. If your goal is losing weight, it might be something to keep in mind
That's a misconception. At low intensity it's true that a greater percentage of the calories expended are coming from fat. But the total number of calories burned is so low, that you still burn more total fat at high intensity in a fixed amount of time, you're just burning more glycogen as well.

What low-intensity activity is good for, is allowing people to exercise who couldn't otherwise, and also allowing people to burn more total calories by light exertion over long periods of time. Simply put, most people aren't in shape to be able to maintain very high intensity for more than an hour or so. (In fact, most of the people that that "guideline" is usually aimed at, aren't even in shape to be able to maintain 85% of MHR for longer than 10 or 15 minutes.) Whereas almost anyone can walk or ride a bicycle at 60% of MHR for one, two or five hours a day and burn hundreds of calories worth of fat doing that.