THE “FAT BURNING ZONE” MYTH
Step onto a treadmill, bicycle, or elliptical machine and you are likely to see a diagram or possibly even a program that is called “Fat Burning Zone”. Sounds great right? Well, lets look deeper at the process and see if it is the most effective fat burning strategy.
The Background:
When the body has been fed (you have eaten within the last 3 to 4 hours) it uses a mix of fat and carbohydrate to fuel the energy needs of our cells. Researchers can quantify this mix with high accuracy in an exercise physiology laboratory. When the exercise is of a low intensity, our bodies preferentially use fat as fuel. Thus, low intensity exercise does predominantly rely on fat to fuel contracting muscles.
As the exercise intensity increases, the body progressively switches to a predominance of carbohydrate utilization. By exercising at a lower intensity a greater percentage of fat is being utilized for energy. This is the rationale for equipment manufacturers creation of the “fat burning zone”.
A Closer Look:
Below is a table of energy expenditure for 60 minutes of cardiovascular exercise at three different intensity levels of 30, 50 and 70 percent of maximum heart rate. As the exercise intensity increases so do the total number of calories burned. You may also notice that as intensity increases the percentage of energy from body fat decreases. However, the increase in calories is substantial enough to out weight the decrease in body fat utilization. You will burn more body fat at a higher intensity level. Thus the “fat burning zone” is a myth. Don’t just take my word for it. Google “Fat Burning Zone Myth” and see for yourself.
INTENSITY Calories Burned % Fat Utilization Total Fat Burned
30% of MHR 300 60% 180
50% of MHR 480 50% 240
70% of MHR 660 40% 264
100% Fat Burning:
Now, I am going to take this example one step further, and change the way you think about burning body fat. The above example demonstrates that the body uses carbohydrates and fat. The carbohydrates come from the food we eat. Let me ask you, what if the person exercising runs out of carbohydrates? What does the body use then?
The human body can only hold about 300 calories worth of glycogen in the liver. Once that is gone, the body then relies completely on body fat for energy. This means that if you exercise when no carbohydrates (Glycogen) are available, you are burning 100% fat!
The more calories you burn, the more body fat that has to be broken down to meet caloric needs.
Many people mistakenly think that the body will utilize muscle for energy. Muscle is made up of chains of amino acids. The body will break down muscle only when it needs amino acids to repair cells. It does not break down muscle for energy. Muscle is not an energy source. People who lose muscle while dieting or restricting calories do so because their body needs the amino acids. A restricted calorie diet is also going to be limited in amino acids. This is why your nutrition program has adequate amounts of protein. This ensures that your body will not have to go hunting for amino acids in your muscle cells.
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