The Truth About The “Fat Burning Zone”

Truth About Fat Burning Zone

For a long time, many so-called fitness experts have been advising people to exercise in their “fat-burning” heart rate zone during cardio workouts. By fat-burning zone, they mean exercising at a low level of intensity, as measured by heart rate, because doing so causes the body to utilize a higher percentage of fat as fuel than high intensity cardio. Certainly, if you are only interested in losing fat, as opposed to sports conditioning, this would be the way to go, right?


The truth is, things like the “Fat Burning Zone” are fancy-sounding ways to justify not working out hard.  As my good friend Luke Carlson of Discover Strength points out, it is a technique people use to “engineer the hard work out of the workout”.

Although it is true that a low intensity routine will utilize a higher percentage of fat as fuel, you will burn more fat on a higher intensity program, which I will explain by sharing with you the results of a 1994 study which appeared in Fitness Management magazine (Pocari, 1994). Before we get to that, let me explain what METS are for those who don’t know.

METS stands for metabolic equivalent. METS are frequently used to measure the intensity and energy requirements of an activity. One MET is equal to the energy expenditure needed for the uptake of 3.5 ml of oxygen per kilogram of body weight per minute at rest. Thus, an activity that requires an oxygen consumption of 35 ml/kg/min would be identified as a 10 MET activity. Some examples of MET values for common activities are as follows:
1 MET- sitting at rest
2-3 METS- walking at 2 MPH
4-5 METS- walking at 3.5 MPH, badminton, softball
7-8 METS- basketball, cycling at 12 MPH, mountain climbing
10+ METS- soccer, wrestling, sprinting

Now, back to the 1994 study on fat burning. The study consisted of 2 groups, a low-intensity group and a high-intensity group. Each group performed an aerobic workout on a treadmill for 30 minutes while having their metabolism monitored (breathing into a tube, like on those Gatorade commercials). The low intensity group walked on the treadmill at a speed of 3.8 MPH (the “fat burning” zone), while the high intensity group ran on the treadmill at a speed of 6.5 MPH. The results were as follows:

Group:                                   low intensity        high intensity

Time:                                     30 minutes           30 minutes

Total calories burned:                  240                       450

% of Carbohydrate as fuel:    60% (144 cal.)       75% (342 cal.)

% of Fat as fuel:                    40% (96 cal.)         25% (108 cal.)

Observe that the trainees in the high intensity group burned almost twice as many total calories as those in the low intensity group in the same amount of time. Total calories is the number one measurement for weight loss; thus, the low intensity group had an inferior workout by that standard. Also note that although it is true that the low intensity group burned a higher percentage of fat (40%) than the high intensity group (25%), the calories burned from fat was actually more for the high intensity group (108 vs. 96).

The results of this study demonstrate what anyone with common sense already knows-namely, the harder you work, the more calories and fat you will burn and the better shape you will be in.

Here’s one last example to bury the “fat burning zone” myth once and for all: This past summer, we all enjoyed watching the 100 meter sprinters in the Brazil Summer Olympics-the fastest human beings in the world. How long did it take these athletes to cover this distance? Somewhere between 9 and 10 seconds, running all out, at 10+++ MET pace. Hardly the “fat burning zone” that is often recommended to us normal humans just trying to lose a few pounds! As you watched these athletes fly, did you see any visible body fat on these people?

I already know the answer: NO. So much for the fat burning zone!

Exciting News!

Rock Solid Fitness will be offering High Intensity Cardio Workouts at our new Dunedin Facility! Visit this site often for the latest news about our move to 2110 Main Street in Dunedin – we will be there in just a few more weeks!

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