By Maria Artime

The body uses or “burns” three sources of fuel for energy.

• These are known as carbohydrates, lipids (a.k.a. fats), and proteins.

Stored carbohydrates are the body’s primary and preferred source of energy. One gram of carbohydrate yields approximately 4 kcal of energy.

Stored body fat, known as triglycerides is an ideal source of energy when doing long bouts of exercise. This is due to the fact that one gram of fat contains about 9kcal of energy, which is over twice the amount of energy derived from carbohydrates and proteins. When the body needs fats, they can be broken down or “burned” via a process known as lipolysis.

During exercise, fats and carbohydrates play the biggest role in energy supply. Which source of fuel is being burned is determined by several factors, including a person’s diet and the intensity and duration of the exercise. For example, if consuming a high fat/low carbohydrate diet, the fat metabolism will be considerably high in comparison to the carbohydrate metabolism during exercise.

There are sufficient amount of studies to show that the body will burn whichever source of fuel it has to burn in the greatest abundance. In regards to exercise intensity, low intensity exercise relies primarily on fat as fuel while carbohydrate is the primary source during high intensity exercise. During low intensity, prolonged exercise the amount of fat utilization will increase linearly with time.

What does this all mean? Putting diet aside (that’s another article all together), the current debate is whether high intensity/shorter duration exercise is better or lower intensity/longer duration will burn more fat. The argument for high intensity is that although the majority of the calories during the exercise session will be coming from carbohydrates stores, the amount of fat burned post exercise is significant enough to produce a high fat burning effect.

This is achieved because the intensity of exercise is high enough to significantly raise one’s core body temperature and resting metabolism for several hours after the exercise session. On the other hand, the traditional long exercise bout of at least 1 hour at a moderate intensity usually prescribed as 65-75% of ones maximal heart rate (MHR) will derive the majority of the calories burned through fat metabolism during the exercise session and is much less stressful on the body. So, what is better?

The answer is; it depends on you.

First and foremost, there are two very important questions you need to be asking yourself. The first is; what is my current physical condition? The second is; how much time do I have? If you are a “beginner” or have not exercised in a considerable amount of time (i.e. over one year), or consider yourself “out of shape” you are better off with the low intensity/longer duration exercise prescription. This is simply because you will not be able to produce the amount of effort during the exercise session required to achieve the post exercise raised metabolic rate.

If you are in decent to great shape and are pressed for time, you are better off with the short duration (20-30min)/high intensity exercise prescription. Here is the bottom line, they are both exactly the same. At the end of the day, the game is played by counting how many calories went in your body versus how many calories did you expend. That equation is the real secret to fat burning.

Studies show that both of these types of exercises will produce about the same amount of over all calories burned. The difference is that the short duration will burn the majority of calories after the exercise session while the longer one burns the majority of calories during exercise session

Most of you who read this will fall into one of the two categories just described above. However, I know that there are some of us who are real fitness enthusiast, are in great shape, and have a bunch of time. You read these articles time and again and wonder what is best for me?

In recent years, a very popular trend has emerged in the fitness industry to cater to your needs. It is called interval training. Interval training combines high intensity with low intensity exercise. It can be done for a short time or longer periods of time.

If you are in great shape and have all the time in the world, you will most likely notice that any form of cardiovascular exercise that you can take your heart rate up to your 92%HRM and then back down to your 65%HRM over and over again will produce the best results. You are combining the two forms of exercise described above and therefore will get the benefits that both produce and burn the most amount of fat during and after your exercise session.

In summary, exercise burns calories. If you are burning more calories throughout the day than you are taking in, your body will begin to burn off excess fat as fuel. Something to think about is the fact that carbohydrates are burned when the body is doing heavy intensity work.

What is the opposite of heavy intensity work? Rest! That’s correct, the contribution of fat as fuel is greatest when the body is resting. So you may be wondering how come you can’t sleep all day and lose weight? It is quite simply a numbers game. When you are resting, even though the majority of the calories being burned are coming from fat sources, the amount of calories that you are burning is too insignificant to make a dent in the overall fat thatyou are carrying. The trick is to increase the total amount of calories being burned!