The Fat Burning Zone – Fact or Fiction?

Live Fit : Fat Burning ZoneWhat is the Fat Burning Zone?

Every now and then somebody will make reference to working out in the “fat burning zone”. This is still common “knowledge” for many gym-goers. But is their an exertion level (or zone) a person stay in to burn the most adipose tissue possible?  Or is this zone a piece of marketing fiction?

I’m not sure how it was initially popularized though, most cardio machines have a “fat burning zone” setting. Maybe they originated it to help boost sales. No matter, the truth is the same, a higher percentage of fat is burned at a lower intensity of activity. Once again, a higher percentage of total calories comes from fat when your body is at a low intensity – than when at a high intensity. This means that, as I sit here typing; I am using a higher percentage of fat than if I was walking, running or climbing stairs, etc.

Sit and Burn?

Cool. Let’s all sit around and burn fat, right? No! That doesn’t sound right, does it? That would be too easy. But walking on a treadmill will burn more fat than running on a treadmill, right? Sort of.  The lower the intensity, the more the body relies on fat for its energy. Turning fat into the usable fuel (glucose then ATP) takes time and oxygen. There is plenty of both available to meet the demands during a low intensity “activity” (or no activity) and less as intensity increases.

Live Fit : Fat burn vs. carb burn

Fat vs. Carb burn “X”

So, you might be hearing that sitting, standing and walking uses more fat than higher intensity activities like running, right? No. These low intensity activities derive more of their energy from fat than from glucose – meaning a higher percentage of fat is being used.

Take a look at the chart to the right. It shows that as the demand for energy increases the percentage of where that energy comes from shifts from fat to CHO (carbohydrates).

Greater Percentage Does Not Equal Greater Calories

Let me explain it this way. If I sit in a chair for an hour I might burn 60 calories. Ninety percent (or so) of those calories will come from fat and equal about 54 Calories. Now, if I jog on a treadmill for one hour I might burn 500 Calories, yet only 50% of those Calories would come from fat. Since 90% is a bigger number than 50% many people interpret this as being a better way to burn body fat. But 50% of the 500 Calories burned running is 250 Calories. Therefore, the total Calories and fat Calories used during the higher intensity activity are much greater (250 Calories is greater than 54 Calories).

Put Another Way

Would you rather have 90% of $1 , or 10% of $100?

Most people would take the $10.

The greater the exertion – the greater the energy use (and fat loss).

The Harder You Work — The More Energy (Calories) You burn

Another factor to consider is the afterburn. The technical name for this is EPOC (excess post-exercise oxygen consumption). I like “afterburn” better, as it is more to the point and easier for most people to understand. Afterburn is the amount of energy above your normal metabolic rate that is being used after an activity. This means, if you exercise really hard, such as heavy weight training, sprinting, etc. you will continue to use energy while you recover due to the elevated state of your metabolic system. This elevated state is a direct result of the need the muscles have to replenish the carb stores within the muscle tissue to be ready for the next event, the body repairing damage and waste products being removed. The afterburn effect is negligible with low intensity exercise such as  in the “fat burning zone”.

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The best way to burn stored body fat (adipose tissue) is to exercise at a high intensity several times a week. Your fat burning zone is a high intensity workout that is a 7.5 or higher on a relative exertion scale (1 to 10) or 75% or your max heart rate. It is not necessary to maintain this high effort for your entire workout, in fact I recommend doing intervals. I will explain intervals in another post. For now, get on that bike, treadmill, track, pool, or crossfit class and bust your butt. The harder the better. Go in spurts with high intensity phases that last 10 to 20 seconds, then recover at a moderate intensity until you recover enough to do it again. Consider running at full speed, then jogging until you are recovered enough to sprint again.

The Bottom Line

The harder you work the more energy you burn and the greater your afterburn AND fat burn will be. Therefore, the fat burning zone is the same as the Calorie burning zone – the more, the more.


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