The Fat Burning Zone

tim_fitbuilt4life

There is a lot of discussion about what is the best fat burning zone to be in. This fat zone is a contentious issue with a number of people offering different opinions. This article investigates what happens in each zone and why its happening.
In order for a muscle to function it needs energy. Muscles have three options for this fuel, namely carbohydrates, fat and protein. Protein is only used by the muscle under depleted circumstances and won’t be concentrated on.

The muscle also has two places that it can find these fuels, within the muscle itself or through the blood stream.

• Blood Stream: Carbohydrates inside the blood stream are found in the form of glucose, fat in the blood stream comes from a process called liposys. This is the process of releasing fat stores from your body and into your blood stream for use as energy. This is the process we want more of when we want to lose our excess body fat.

• Intra muscular energy: Inside the muscle the carbohydrates source of energy is Glycogen, which is a mixture of glucose and water. The fat store inside the muscle is called triglyceride. The muscle would prefer to hang on to the internal stores as they are limited and it would prefer to use them only when necessary.


When using energy your muscle uses a mix of carbohydrates and fats, this is based on a number of factors, one of them being the intensity and duration of the activity.

Fats require more oxygen than carbohydrates to burn. As a result this implies that as the intensity of the exercise goes up and less oxygen is available the body shifts from a fat burning zone to using carbohydrates for energy in order to maintain the activity. This doesn’t however mean that less fat is burnt.

Fat provides the bulk of energy at lower intensities and as the intensity increases the amount burnt is increased, just in a lower percentage to the contribution of carbohydrates. So as intensity is increased more fat is burnt. This lasts up to moderate intensities and begins to taper off at higher intensities. This was the basis for the low intensity fat burning zone. This doesn't however give the full picture and what becomes more important than fat vs. carbohydrates is rather where the source of this energy is coming from.

So as a person does low intensity exercise, such as walking his intensity could be described as 2 out of 10 on the scale. At this point fat would be the primary source of energy as oxygen is plentiful. The muscle would choose mostly fat from the blood stream as it a much more plentiful source of energy than the fat stored inside the muscle. The rest of the energy would come from glucose. This was traditionally called the fat burning zone by most people advocating low intensity activity. Although the fat source being used is the one we are looking for, the total amount of calories burnt is ineffective as any form of weight loss.

So we ramp up the intensity and start working harder, running moderately, say 6 out of 10 on the intensity scale. Our muscles need more oxygen and energy so our heart starts beating faster to get the blood to the muscle quicker. Our muscles produce heat which needs to be released, so blood carries this to our skin. This increase in requirements for blood to run these two processes takes blood away from the procedure of loading fat into blood stream. The increase of this process as an energy source to the muscle therefore levels off; however the muscles rate of burning fat still increases. To make up for the deficit the muscle turns to it own fat stores (triglyceride). This is most optimal fat burning zone however we have not reached the intensity levels required for HIIT.

Our intensity is increased again to working very hard, about an 8 out 10 on the intensity scale. Our muscles are now not getting sufficient oxygen so the muscle turns more to carbohydrates than fat. As with the fat, the greater the intensity, the less supply of energy is in the blood stream, the more the body turns to its own stores. In this case it burns the glycogen in the muscle.

If intensity is increased again beyond the point where the body can consume enough oxygen, 9 or 10 out of 10 on the intensity scale, the body starts to create lactic acid at a rate faster than it can clear it out of the muscle. At this point the muscle begins to fail.

So if you only take into account the fuel type, carbohydrates or fat, the maximum fat burning zone occurs at a point of moderate intensity (and not low intensity). This however doesn’t explain why High Intensity is much better for fat loss than medium or low exercise in the fat burning zone. The secret is in the afterburn or the period directly after the high intensity. This is what makes HIIT work.

laddyboy

Thanks for the info....this explains a lot.

jroulo

Bump.

Amandac6772

I'm a true believer in the afterburn effect of HIIT workouts.