This is a question I get very often from people because there is a lot of misinformation in the fitness field. There are several reasons why high intensity/short duration cardiovascular exercise is superior to low intensity/long duration. High intensity/short duration cardiovascular exercise, such as sprinting interspersed with periods of rest then sprint repeated several times (i.e interval training), is far better for fat-burning and for improving cardiovascular fitness (V02 max).

The reason people believe low intensity/long duration cardiovascular exercise is better for fat-burning is because they are going by the target heart rate/zone training belief. The advocates of training in the right target heart rate zone point to a greater amount of fat being burned at a specific intensity. They say that if your training intensity is too high you will be burning carbohydrates for fuel and that you need to be at a certain lower intensity zone to burn fat. The people who promote this method of training are missing the whole point of exercising and there are several reasons why this method of training is flawed. It is true that at a higher intensity a greater percentage of carbohydrates are used for fuel than at a lower intensity but the total amount of fat and calories burned is greater at a higher intensity. Also if training at a lower intensity is better because it burns a greater percentage of fat than carbohydrates then sitting on the couch watching television is the best way to train because 95% of the calories burned at rest are fat.

That leads me into the final and most important reason why target heart rate training for long durations is flawed. The greatest amount of fat and calorie burning are done in the hours after exercise and the degree to which this happens is in direct proportion to the intensity of exercise. Exercise is the stimulus to put you into an enhanced fat burning zone and if the intensity is high you will elevate your body's fat burning mechanisms and hormones for hours and hours after exercise. Exercising at a low intensity does not achieve this same effect. If the workout is done correctly a person can elevate their metabolic rate (rate at which you burn calories) and growth hormone levels (the most potent fat burning hormone in the human body) for 24 to 48 hours later. That is 24-48 hours of enhanced fat burning. This makes the amount of calories you burn during exercise minimal in the grand scheme of things.

As you can see intensity of exercise, not duration, is the key component and one of the best ways to get the intensity level up is to exercise using interval training. Sprinting interspersed with periods of rest or low intensity training such as jogging, like I stated earlier in the article, is an example of interval training. This type of exercise is much more anaerobic than aerobic in nature with the duration being short. When I have my clients do their cardiovascular or anaerobic training the workouts rarely lasts more than 20 minutes with some people getting the desired training effect in 8 to 10 minutes or less. This being said I advise one to slowly and gradually increase the intensity of their cardiovascular exercise/anaerobic interval training routine and not just jump into high intensity exercise such as sprinting. Everyone's starting point is different and what one person may consider high intensity the other may consider low intensity and vice versa.

Many times it takes a few workouts for my clients to find out what their correct starting point is. From there it is important to vary the workout on a regular basis and make changes to it. The human body can adapt very quickly to the same program no matter what type of training you are doing. Most people never think of changing their workout programs and even if they do they only think of it as it pertains to weight/strength training. Making changes to your anaerobic interval training program is just as important to your long term success as making changes to your weight/strength training program. Discussing the type of changes, how to make them, and when to make them would beyond the scope of this article but the point is to not let the body adapt to a specific workout. The body adapts to anything and everything from the type of exercise, to the rest intervals, to the time of the high intensity intervals so varying all of those are important for long term success.