Many people still believe that since you burn more fat calories during a moderate-intensity session, this is the best way to burn body fat. While it is true that working at a moderate heart rate will make your body burn more calories from fat, the more important thing to look at is the total number of calories you burn.

When you perform high-intensity interval workouts, you burn more calories per minute than when you work out at a lower intensity. Granted, you may not be able to last as long, but the number of calories you burn during both sessions is actually quite similar. But the advantage of interval training is that it causes your body to burn a significant amount of calories after you have finished your workout. This means that you will continue burning calories at a higher rate for numerous hours afterward, thus causing the total number of calories burned throughout the day to be higher, translating into a greater fat loss.

High-intensity interval training also tends to help preserve muscle tissue, whereas long moderate-intensity workouts can become catabolic in nature (breaking down muscle).

However, an important point to keep in mind is that you cannot perform high-intensity cardio every day; either alternate high- and moderate-intensity sessions or space out your high-intensity workouts within the week. If you do wish to perform some moderate-intensity sessions, they should last at least 20 minutes so that your body can get into its fat stores; for the first 20 minutes or so, you will most likely just be burning carbohydrates that you have consumed in recent hours. For your intense workouts, you can see benefits — both from a fat-burning and a health benefit standpoint — from doing short 6- to 10-minute workouts.