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The Fat Burning Zone Myth: Don’t Be Fooled

By Marc Perry / July 1, 2017

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 workout to optimally burn fat., 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 if that is your goal.

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 two places: fat 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:

30 Minutes of Exercise Fat Calories Burned Glycogen Calories Burned Total Calories Burned
Low Intensity Group (50%) 120 80 200
High Intensity Group (75%) 140 260 400

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 the fat 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.

Want to burn fat without losing muscle fast? Then start my 12-Week Body Transformation Program.

Show 3 References

  1. Source: Bryant, Cedric X. 101 Frequently Asked Questions about “Health & Fitness” and “Nutrition & Weight Control“. Sagamore Publishing, 1999.
  2. Scott, Christopher. “Misconceptions about Aerobic and Anaerobic Energy Expenditure.“Journal of the International Society of Sports Nutrition 2.2 (2005): 32. BioMed Central. Web.
  3. 3. Available at: http://www.builtlean.com/2011/06/29/afterburn-effect-of-exercise-qa-with-dr-christopher-scott-phd/. Accessed March 14, 2013.


  • Katherine says:

    I used to be down on extended periods of strolling for exercise, but I have come to realized that one of its most underrated functions is to get people in the worst shape out of the house and away from easy snacking when they are most bored. I now recommend it as a "gateway" exercise.

  • uncadonego says:

    Agreed Katherine, going for a walk is definitely a good way to curb the desire to mindlessly snack and get your body moving. :-)

  • Michi_Modele says:

    They Neglect to tell you that though your body is burning more calories at HIIT it is getting the majority of these calories by consuming your existent muscle, sure you'll lose the weight quicker but you'll be losing muscle, and we all know the higher your muscle content the faster metabolism, so at some point even though you're training your ass off, your weightloss will plateau. Slow and steady wins the race...

    • Marc Perry, CSCS, CPT says:

      Hey Michelle, thanks for your participation!..but the exact opposite of what you are saying happens when you do HIIT - you maintain your muscle and lose fat. Slow and steady is definitely one very viable option to lose body fat, but there is no question that interval training helps burn fat faster while retaining muscle mass. There is mountains of research about this, check out my interval training article on BuiltLean. If you have a research report or two showing muscle loss with HIIT and a non-extreme calorie deprivation, please share.

  • JJay_schwarb says:

    Brilliant article.

    • Kristin Rooke, CPT says:

      Glad you enjoyed it!

      -Kristin, BuiltLean Coach & Managing Editor

  • Tolga says:

    Thank you for this informational article. High intensity training is a great way to burn calories in a very short period of time however your body can't last long with high intensity. In the example, you say that one group burnt 39 calories and other group burnt 65 calories, cycling group can continue their exercise for hours but sprinter group can't do it so long. Therefore, lower intensity training seems a better way to burn more calories in total. After doing HIIT, my body can't recover for several days also.

    • Kristin Rooke, CPT says:

      Thanks for sharing your insights and experiences! While it's true that you can typically workout longer while performing lower intensity exercises, and therefore burn more calories, it's not only the calorie burn that contributes to the weight and fat loss effects of high intensity intervals. HIIT also elicits a hormonal response (specifically, catecholamines, cortisol, and growth hormone), while simultaneously affecting heart rate, venous blood glucose, and metabolic reactivity. All of these responses play a role in the effectiveness of HIIT to reduce body fat. All that being said, because HIIT is so metabolically intense, it's not a workout style you want to do more than 3x per week. It has a huge effect on the central nervous system, which is why it's a workout method that takes longer to recover from.

      -Kristin, BuiltLean Coach & Managing Editor

  • S. Pal says:

    Hello and thanks for the article, this clearly shows the total calories burnt during high intensity cardio (75% of max. heart rate) burns way more fat calories specially because of the after burn effect, something I learnt more precisely today. However, it also shows that high intensity cardio burns a LOT more (more than 3 times!) muscle glycogen than low intensity cardio , and that's bad, because if we've more muscle mass, we burn calories more (I've heard it, but I can't cite a reference!). So, why, combining all these conflicting factors, high intensity cardio is better? Thanks in advance!

    • Marc Perry, CSCS, CPT says:

      Sorry for not responding to this sooner, it slipped by me! Glycogen is stored in both the liver and muscles. Most of the fat-burning happens after the exercise with high intensity interval training, which is really the point of the article. Comparing the relative percentages of how much fat is burned during the workout for HIIT vs. Steady State does not reflect the true picture of what's happening. Thanks for your question

  • Frank says:

    Say that to my knees. They love low intensity workout, just enough to work a sweat. But I will keep at it for hours a day no problem. But anything near high intensity cardio, and it hurts as hell and I feel I have done "enough for the day".

    While I agree that food intake should be your main source of fat burning, being able to do low-intensity workout while watching your favorite tv-shows is a great addition to that. And something you can keep doing every day till you are at your optimal weight.

    HIIT is scary, intensive, and potentially painful. Leave that for the pro's who want to really increase their physical capabilities. Low intensity workouts, preferebly in moments where you'd otherwise be sitting (like watching tv) is a great option for fat-burn aka weight loss.

    I've seen a friend drop weight like crazy, his method? Just binge watch his favorite tv-shows while on a stationary bike. He'd watch em anyways, just now on a bike :)

    Become a sci-fi fan if you aren't already, start with Star Trek then do Stargate. You'll have lost all your weight before you finish them :)

    • Marc Perry, CSCS, CPT says:

      Thanks for sharing your thoughts, Frank. HIIT is certainly not the only way to reach your goal weight and you are absolutely right - it's not for everyone.

  • Manuel says:

    i think i agree with this article, thanks for u Marc Perry.. In http://www.webmd.com/diet/default.htm says " Weight loss is a matter of simple arithmetic: To shed pounds, you must burn more calories than you consume. And when it comes to burning calories, the greater the exertion, the greater the rate at which calories are burned."

    • Kristin says:

      Totally, Manuel! That's absolutely right. And an added bonus to more intense exercise, like weight lifting and HIIT, is that it induces the afterburn effect. That essentially means that you're burning more calories for hours after you're done exercising. These workout methods also help keep your metabolism high and tell your body to keep lean muscle mass, even when you're eating a reduced calorie diet. Glad you enjoyed the article.
      -Kristin, BuiltLean Coach & Managing Editor

  • Luis says:

    Hello Marc,

    What would be your recommendation on HIIT vs. Fat burning zone cardio when you are on a limited caloric intake(around 1500cal/day)? I am currently doing two hours of low-intensity cardio per day(at 0330 and 1900), and I do weight training on a four days on, one day off rotation. I am 30 years old and would like to get down to about 175lbs and somewhere between 10-15% body fat. I have tried HIIT training, but I often find that I do not have the energy when I am weight training or the next time I do cardio. I also tend to take longer to recover physically. So I limit the HIIT for once every 3-4 days. Yes, I can burn 1000 calories an hour doing a high-intensity workout, but I cannot do that twice a day, six times per week. Whereas walking 3mph, at an incline of 8-10% (depending on what my hr is), I can do twice a day, six times per week. Thanks in advance!



  • Marc Perry, CSCS, CPT says:

    Hey Luis - As long as you are regularly exercising and creating a calorie deficit, you should be able to lose the fat. You have a very low calorie diet, I would probably bump it up to 1800 to make things more manageable if you are exercising so much. If you were more sedentary, 1500 could work but it would still be a bit low. The goal would be to lose 1 pound of fat per week like clockwork. The method of exercise is less important then getting the calories right and sticking with it. The purpose of this article was more from a time-efficiency standpoint, HIIT is better than steady state and burns incrementally more fat, but either works. So do what works for you and you want to do