To lose 1 pound of body fat, you must burn 3,500 calories more than you consume over a period of time. In a long cardio workout, you exercise at a consistent, moderate level for the entire session; in a high-intensity interval training workout, or HIIT workout, you alternate periods of moderate intensity with bursts of high intensity. Either type of exercise can help you lose weight. Talk to your doctor before beginning an exercise program.
Fat Burning Zone
When you exercise at a low to moderate intensity, about 60 percent of the calories you burn come from fat stored in your body, according to physical trainer Cedric Bryant. When you exercise at a high intensity, your body uses carbohydrates for fuel instead, and only 35 percent of the calories you burn come from stored fat. Because of this difference, a moderate exercise level that does not elevate your heart rate dramatically is sometimes referred to as the fat burning zone.
One of the advantages of moderate-intensity exercise is that you can sustain it for a long time, because you are not working hard enough to fatigue your system. Unless you are in particularly good physical condition, you probably will not be able to do HIIT for as long as you can exercise at a moderate pace. However, according to Michael Bracko of the American College of Sports Medicine, you don't have to -- you can get the same benefits from a shorter HIIT workout as you get from a longer, more moderate workout.
Even though a long, gentle cardio session burns a higher percentage of calories from fat, a HIIT workout of the same length will help you lose weight faster. When you exercise at a higher intensity, you burn calories at a much faster rate. Only 35 percent of them come from fat, but 35 percent of a high number can be more than 60 percent of a lower number. Additionally, HIIT speeds up your metabolism -- you can burn extra calories for a whole day after high-intensity exercise, according to Bracko.
HIIT works your body harder than long cardio sessions do, so all other things being equal, HIIT will give you faster results. However, it is hard on your body, and you should not attempt it unless you are already in good shape and looking for a way to push yourself. If you need to lose a large amount of weight or you are unaccustomed to exercising, start with gentle, moderate exercise until your fitness level improves and your doctor advises you to increase the intensity of your workouts.