The Fat Burning Zone Myth: Don’t Be Fooled

 by Marc Perry, CSCS, CPT | April 1, 2013 | Updated: March 24, 2013 | 11 comments

The fat burning zone is one of the most pervasive myths in the fitness industry that just won’t go away. Magazines constantly promote workouts in the fat burning zone as an effective way to burn fat and most cardio machines around the world have some type of sticker, or image clearly visible (see image to your right).

The idea is if you keep your heart rate in the “fat burning zone,” which is roughly 55% to 65% of your max heart rate, then you will magically burn more fat than at higher levels of exercise intensity.

Why work harder, when you can take it easy and burn more fat, right?

Well this, my friends, is why the fat burning zone myth is so attractive. The truth is at best, the fat burning zone is very misleading, and at worst, it’s complete misinformation.

This article will teach you 2 specific reasons why the fat burning zone is a myth so you can workout to optimally burn fat.

The Fat Burning Zone Confuses Absolute vs. Relative Fat Burn

To understand the fat burning zone myth, you need to understand how your body uses energy during exercise. To keep things simple, during exercise your body draws energy from primarily two places: fat stores, or glycogen stores. Glycogen is stored carbohydrates in your muscles and liver.

The fat burning zone was conceived because at lower exercise intensities more fat is burned relative to glycogen. Isn’t this awesome? Now you can hang out on the couch and lose a bunch of fat. I hope you are starting to smell something fishy with this idea of a fat burning zone.

At 50% of your max heart rate, your body burns a ratio of 60% fat to 40% glycogen. At 75% of your max heart rate, the ratio is 35% to 65%, and at even higher intensities, the ratio is even lower.¹

So why the heck would you want to workout so hard if you burn so little fat?

The reason why is because it’s all about calories. You burn a lot more calories when you workout intensely than you do when you are sitting on the couch.

So here’s what the breakdown looks like assuming 30 minutes of exercise for a low vs. high intensity group. The high intensity group will likely burn double the calories as the lower intensity group, or 200 vs. 400 calories:

So now you can see you burn more fat calories at a higher exercise intensity than a lower exercise intensity (140 vs. 120) despite a smaller percentage of fat being burned. But I know you need more convincing because the higher intensity exercise represents only a 20% difference in fat calories burned for a 50% increase in intensity. Not a good tradeoff.

There is something important we are missing in these calculations, which you will learn in the next section.

The Fat Burning Zone Has No Afterburn Effect

When you exercise at low exercise intensities, you burn very few calories after the exercise is completed. When you exercise intensely such as during a HIIT workout, there is a metabolic disturbance that burns calories after the workout is completed. This is known as the afterburn effect.

Estimates of the afterburn effect vary wildly depending on the exercise method, the intensity of the workout, and even how its measured.

In a study by Dr. Christopher Scott and the University of Southern Maine, the total calorie burn of low intensity exercise vs. high intensity exercise was examined. A low intensity exercise group cycled at a steady rate of 3.5 minutes. The higher intensity exercise group required three 15 second sprints as fast as the subjects could run.

What was the difference in calorie burn? Quite substantial.

The cycling group burned 29 calories vs. 4 calories for the sprinting group during the exercise. But when you take into account the calories burned after exercise, or the afterburn effect, the numbers look much different – 39 calories burned for the cycling group vs. 65 calories burned for the sprinting group. A surprising 95% of the total calorie burn occurred after the sprinting exercise!² Keep in mind the cycling group exercised for almost 5x longer than the sprint group (3.5 minutes vs. 45 seconds).

If this isn’t enough convincing, one study showed a significant amount of fat was broken down from fat stores in the muscle following high intensity cycling sprints.³ During high intensity exercise, you are burning primarily glucose, but after is when you burn the fat. This is the crux of the fat burning zone myth and the afterburn effect.

While low intensity exercise certainly has its place within an exercise regimen, relying on exercise in thefat burning zone to burn fat is not an efficient approach. Contrary to popular belief, getting up early in the morning to do low intensity cardio on an empty stomach will not help you lose more body fat versus other more intense methods. For busy people, interval training and circuit training workouts are substantially more efficient to help you burn far more calories in much less time, and burn more fat in the process.

With all that said, I highly recommend not relying on exercise to “burn fat” to get lean. In the context of a fat loss program, exercise helps you keep your muscle, stay fit, make modest increases to your metabolism, and burn some fat. Because it’s a scientific fact that you must eat less calories than you burn to lose fat, nutrition has a much more powerful impact on this equation and consequently, it should be your main focus.

http://www.builtlean.com/2013/04/01/fat-burning-zone-myth/?utm_source=newsletter&utm_medium=email&utm_content=fatburning&utm_campaign=weekly+newsletter&inf_contact_key=77330cf6789fc5a340b3f489d91a34868691cbd972dd69ad9a1bf6c7ce73975b

Thanks for this. Very informative. I never pay attention to the fat burning zone anyway, but good to know that I'm doing something right. Also, didn't know about the afterburn effect. Freaky.

Glad you enjoyed.

Oh yes , the afterburn effect is amazing.  I havent done a long time cardio session in probably 2 years.  I either do my cardio through supersets which will activate the afterburn effect or a High Intensity Interval Traingin (HIIT).  My favorite is either the 30/30/30 or M-100.  Both takes 3-10 minutes.

Yes, if anything, you gotta be in the "Cardio Zone". I find that heart rate zone more accurate at the gym to coincide with higher intensity training and actually better fat burning.

Not that I really need to burn fat lol. All I am doing lately is trying to get extra definition, lean cut muscle for my honeymoon in the next month or so! I've got 4 solid abs, the blasted bottom 2 are the hardest because that is the one place a body naturally stores a bit of fat pooch.

Right now I'm 150-155 pounds with only 6% body fat.

I basically follow the Advocare 24day challenge meal/workout plan, but I use my own supplements rather than their overpriced stuff.

I typically run for about 40 minutes a day, starting at 4mph, then jump to 6.7 after 5 minutes, and later gradually increasing by .3 every 5-6 minutes.

I usually end up doing ~5miles.

Is this good, or should I try something else?

It depends on what you want.  If you like long runs then go for it but a HIIT can burn just as many calories in a fourth of the time. Plus you will be losing calories after the workout as well.  If you are running a triathalon or some kind of event it would be useful doing endurance runs but if you are doing it for looks and you want to save time then do an HIIT.  They are hard but well worth it.  If you run anyways try a 30/30 and see if you like it.  30 seconds of jogging about 50-70% max and then sprint  at 90-95%  for 30 seconds.  Alternate that for about 5-10 minutes and see if you like it.

I've done that a couple times and it was excrutiating. But, if it saves time, I'll give it another shot. Didn't know how much it actually burned.

Are you measuring your bf% yourself?  at 6% bf you should have a full 6 pack.  usually 8-12% bf is when you see your 6 pack.  If you truly are at 6% bf I'd recommend doing some ab building routines, although this may require you to take in a little extra calories to build some muscle.  

Either way congrats on the marriage and glad to see you taking care of your body :)

You should try varying the tempo abit, for example, sprinting for 2 minutes, then slow jogging for one minute, sprinting for another 2 minutes

I usually stick to your method of slowly increasing the tempo tho, i find easing myself into the cardio and making it get more rigourous keeps me going longer.

Also, ive never understood people walking on treadmills, saying their gonna burn fat, if your gonna go gym, make it worth it with the time you have. Sprint on that treadmill like your rocky with the eye of the tiger!

Why are you so persistent in never including a source of the article??