Fat Burning and Calorie Expenditure
You will use different sources of fuel to produce energy, depending on the intensity of exercise. The lower the intensity of exercise, the higher the percentage of fat used to produce energy. That is why it is often said that you should exercise at a low intensity for a long period of time to burn fat. To a certain extent that is true, but, if you have a limited amount of time to exercise, you would burn more total calories working at a higher intensity.
If your goal is weight loss, it is important to make sure that you expend more calories than you consume. Building muscle helps to increase your basal metabolic rate, so that you burn more calories all day. At rest, each pound of lean muscle burns between 35-50 calories a day. Building an extra 10 pounds of lean muscle could burn as much as 500 calories a day. Each pound of fat contains 3500 calories, so in one week you could lose 1 pound of fat just from having those extra 10 pounds of muscle. Maintaining that increased lean muscle mass for a year could make a 50 pound difference in your bodyweight.