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.
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- Source: Bryant, Cedric X. 101 Frequently Asked Questions about “Health & Fitness” and “Nutrition & Weight Control“. Sagamore Publishing, 1999. ↩
- 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. Available at: https://www.builtlean.com/afterburn-effect-of-exercise-qa-with-dr-christopher-scott-phd/. Accessed March 14, 2013. ↩
How/where exactly does low intensity exercises fit an exercise routine? I loathe cardio so I do it all as HIIT & I rest as little as possible when strength training. Maybe yoga? But even in that I do quick flow Vinyasa which can be intense
great article! I always see people walking on the treadmill at some steep inclines…somebody should tell them, its all about the HIIT!
Suffice to say, I am a firm believer in incline training for several reasons:
1. It’s much easier on the joints and targets the hamstrings and glutes
2. Increasing the strength of the hamstrings and glutes helps to strengthen, support, and stabilize the knee.
3. And by the same token, a 15% incline at a speed of 3-4 is no joke either (especially when you perform it hands-free) and is relative to a speed of 6 or 7 on a flat, or stair machine at level 5
In conjunction with various HIIT/circuit burst movements for 1-2 hours, this style of training presents an adequate workout for me.
True…but you can do low intensity for hours and burn a lot of calories if you’ve got the time.
You can also do it every day without concern, if I walked an hour every morning before breakfast that would burn a lot of calories over a month.
Yes, sure John, if I’m watching the latest episode of Castle like last night, I’m sitting anyway…might as well pedal. So sure, burning calories low intensity is OK, but in addition to…not in lieu of the real workouts.
HIIT is promoted as being one of the most effective cardio-based workouts for fat loss. At the end of an HIIT session, I see that I burn about 25-30% more calories than a normal cardio workout but I feel more than 2X tired. Is this the way fat loss is supposed to work?
@Sree – Fat loss works by eating less calories than you burn. HIIT can assist with this by helping you burn more calories in a shorter period of time and helping increase your metabolism post workout. The fact you feel 2x more tired is because the workout is more intense.
Did he say in the article that you burn more fat when your do lower intensity training? Because I don’t understand
Hi Saurav – that’s correct. Your body burns more fat during lower intensity exercises, and more glucose during higher intensity exercise. While that makes it sound like low-intensity, long-duration is the way to go for fat loss, that’s not quite the case. Doing HIIT induces the afterburn effect, which means that you’re burning more calories for hours after you’re done exercising. It also encourages your body to maintain lean muscle, so that you mostly lose fat while following a reduced calorie diet. By doing HIIT and strength circuits, you can achieve that lean & muscular build.
Personally, I think that doing 1-2 days of HIIT and 1 lower-intensity cardio day is ideal (in combination with strength training 2-3x per week). This combination helps you build a solid cardiovascular base of fitness while also challenging your speed and power.
At the end of the day, nutrition plays the biggest role in fat loss. You have to eat fewer calories than you burn if you want to lose fat and weight. With the right combination of exercise and nutrition, you can absolutely get lean and strong. Hope that helps! If you have more questions, feel free to ask.
-Kristin, BuiltLean Coach & Managing Editor
I was quite lean one year from doing a lot of walking and having less than enough sleep. Except for the walking to and from work, I hardly did any exercises. So it is possible (for me) to do low intensity exercises and lose weight. Now, I do at least 2 interval style of at least 15-minute workouts a day, seven days a week, and I still don’t look as lean as when I was then. On the positive side, the 14 mini-workouts per week lowers my stress level.
@Ken_K – Absolutely you can do low intensity exercise and lose body fat. The point of this article was to dispel the myth that low intensity cardio is optimal for fat loss, which I don’t agree with. At the end of the day, any exercise is going to help you burn incrementally more calories than if you weren’t exercising, which will certainly help. I also wrote an article about 30+ reasons to exercise in addition to body fat loss => 31 Reasons To Get In Shape & Exercise. Good luck!
When I am in a calorie deficit, I deplete my glycogen stores…so if I am in that state won’t HIIT burn my muscles instead? I would think if the goal is fat loss, on top of the calorie deficit, the best exercise beyond weight training would be hours and hours of slow walking. To minimize the muscle loss. Am I missing something. I think HIIT would be better to increase your fitness level when you are not in calorie restriction.
Ha! Ha! I used to worry about getting huffy and puffy and tired…..until I realized that was the point!!!
A lot of of people take up exercise not necessarily to get lean. One of the benefits of regular moderate intensity cardio ( 20-30 minutes of high heart rate exercise at least 3 times per day) is supposed to be a reduction in the risk of coronary artery heart disease and also prevent hypertension, metabolic syndrome etc. I think this effect is independent of the effect of cardio on fat loss .
Would the cardioprotective benefits be the same for moderate cardio, high intensity cardio and HIIT ? Any studies which provide a clear answer? Thanks
@zorba – there are a lot of studies that show the benefits of HIIT from both a cardiovascular improvement and fat burning perspective.
I have HIIT references at the end of these two articles:
1) High Intensity Interval Training (HIIT): Best Cardio to Burn Fat
2) Get Cardiovascular Benefits Without Doing Cardio? Here’s How…
Hope that’s helpful!
I am eating a nice fresh apple as I read this 🙂
Yet Another helpful article Marc, you seem to have answered almost every question there is in fitness
@Dan – Thanks a lot, Dan!
great article as always Marc! i agree with what you say and from my personal weight loss experience i think that the “fat burning zone” is, or should be, geared more towards people with a lot to lose. when i started working out i would do low intensity cardio for long periods of time, usually at least an hour, hour and a half, six to seven days a week and it worked, i lost 2, 3, 4 pounds or more per week but i also ate a lot less than i ever had before so i would end up with big calorie deficits at the end of the day. the age old calories in, calories out does work for fat loss, and for larger people, the lower intensity is safer. exercise is rough on bones and joints when youre 100 or 150+ lbs overweight and also you dont usually have a very good muscular structure or the balance to support HIIT at that time so i think thats where the low intensity has its place to get a person accustomed to working out and conditioned to be able to handle higher intensity exercise down the road. oh, and i also think you really hit the nail on the head in your last sentence, diet really is as important, more important really than anything when youre just looking to lose fat. i really see that now that i weigh so much less and i have less to lose. when im not on with my diet, i dont lose no matter how hard i work. it sucks, but you really cant outwork a bad diet!
Thanks for sharing Mike!
Thank you for this article Marc.
Your writing always make a clear difference between all what’s posted on the internet.
Furthermore, it correlates and bring answers to my personal research
It’s been 8 months now that I tested various Hiit methods and grabbed data with a cardiofrequence meter.
What I discovered that was pretty well working for me is the following:
Subject : male – 47y.o – 1.63m – 63kgs – 9%bf
engine : elliptic
180sec warmup low intensity (level 3 on elliptic)
9 x 24sec highest possible intensity (level 20 to 25 max on elliptic)
9 x 36sec low to no intensity (level 3)
180sec cooldown low intensity (between level 5 and 10 due to hiit stress)
this makes a 15mins Hiit routine allowing me to burn 300+Kcal
Concerning heart rate:
at warmup : around 65% of max, mine being 173bpm (220-age)
during Hiit : between 75 and 95%
at cooldown : from 90% to 65%
Very long and efficient EPOC, I could feel I was kinda breatless for hours after the workout.
Using low intensity I achieved the same result in about one hour (static bike) but then no EPOC at all.
Thanks for the references Marc. By the way, when I say cardiovascular improvement, I didnt necessarily mean improvement in heart/cardiac muscle and function- what I was looking was demonstrable improvement in the rates of atherosclerosis and coronary artery disease.
@Mark: In your chart, heart rate zones over 85% are considered in the ‘danger zone.’ How does that fit in with doing HIIT? I can get my heart rate up to 182-184 (Which is over 100% according to the max heart rate calculators ;b) and always do when doing HIIT. A few times I got it up to 194! I thought it was an error the first time, but it happened a second time and both times I was so tired afterward I slept for the rest of the day.
On a search I saw you can damage your heart doing HIIT but I was not able to find out much in the way of details. I assume this is true? Or does the body protect itself? Another site commented that it is hard to know one’s true max heart rate as it is really hard to get your heart to max out, and the estimates are broad estimates. (yep the devils is in those darn details 🙂 ) So, as the charts are just an estimate, how hard should you push yourself? I wonder if going to 182 is too high, but I have never suffer any repercussions.
Also, thanks again for another great article!
Hey Kristin, I think the “danger zone” should probably be a separate article! I think intensity really depends on fitness level and age. For someone who is fit and athletic, 95% of max heart rate is what is expected in a tough workout. 85% of max heart rate is definitely NOT the danger zone for someone who is in good shape. For someone who hasn’t exercised in a few months in their 70’s, 85% of max heart rate may cause nausea etc. and is likely dangerous. I wrote an article about max heart rate and how it can be highly variable => How to Calculate Max Heart Rate?. In my opinion, if you are concerned about your workout intensity, I would wear a heart rate monitor and cross reference how you feel with your heart rate. Also consider as you get in better shape, it will be harder to maintain a higher heart rate.
Hi Mark. I am new to workouts, started them a couple of months ago. Before starting, I made a meticulous research on how to do it and methods in more than a hundred sites (I am not exagerating), papers, and other sources. I am on my 50s, lots of work, no time to lose with unnefective techniques. I can tell you that your site and your propositions, methods are the most logic I ever found. They really are bringing me results. I subscribe to your site with another one as the basis for information for my workout programs. Thank you for that. I do not want to get out of the subject of this article, but by reading your comment above on the nausea feeling. I used to practice karate when a teenager. I remember having strong nauseas at that time when doing the aerobic exercises. As I grew older, nausea reduced and since 10 years ago disappeared no matter how much I do aerobic exercise, including HIIT. Is that something I should check? Thank you for your advice.
@Phil – Sounds like you are in better shape, you are more properly fed/hydrated before you workout, or maybe as you aged you became more accustomed to exercise. Any way you slice it, it’s a positive thing that you are not getting nauseous, so I don’t think there is anything to get checked out. Thanks for the kind words regarding the site and happy to hear you are doing well with the workouts!
Ha! I gave you a new topic to write on ;b
The Max Heart Rate article slipped under my radar. Sweet, statistics/standard deviations! Thanks!!! That explains everything, and I think I am good for my high end zone.
I do wear a HR monitor (which is why I knew where I was at) and I know my HR tends to run a bit high anyhow (I think I am one of those high beaters?). I’ve been working out for many moons now though, so I don’t think I will see a huge improvement over where I am at. I had my V02max and lactic threshold tested not too long ago. Doc said I could improve on the lactic threshold a bit but but the VO2max looked fine. Hey, there is another article topic. Can’t say I fully grasp VO2max & lactate threshold, but I was getting some other tests done and they weren’t that much more to add on.
@kristin – sounds like a plan. Will consider a VO2Max/Lactate Threshold article, but it may be too technical for most readers!
Excellent article. There is no doubt that your method works well.
I thoroughly enjoyed both this and the “Best Hit Treadmill Workout” article. Quick question though, Is there a substantial difference between using say an elliptical vs. a treadmill? I have very bad knees is why I ask this and 5 days a week running leaves me in serious pain.
Hi Ben (sorry I’m not Mark) but the elliptical is not as high impact as running, which is why it is not as hard on your knees. Personally, I’d stick with what does not cause you pain (your knees are probably telling you something). As long as your heart rate is getting up to where it should be on the elliptical, your cardio system isn’t going to know the difference. You should be doing something like weights though to counter not doing high impact cardio to keep your bones strong. Alternatively, you can crosstrain, like doing elliptical one day and running the next. I can only run so much myself due to a foot injury, so I intermix my running with biking 🙂
Thanks for the “advice”, i love to walk for hours, so now if i go do it everyday i will feel like I’m doing good for myself and maybe see some results.
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.
Agreed Katherine, going for a walk is definitely a good way to curb the desire to mindlessly snack and get your body moving. 🙂
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…
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.
Glad you enjoyed it!
-Kristin, BuiltLean Coach & Managing Editor
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.
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
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!
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
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 🙂
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.
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.”
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
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!
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