T Nation

Fat Burn Zone Myth


I saw this mentioned in another thread, but I think it deserves a thread of it’s own.

The “fat burn zone” heart rate is largely a myth from what I’ve studied. You will burn more calories (from fat) at a higher intensity than you would at a lower intensity for the same amount of time. The misconception comes from the PERCENTAGE of energy that comes from fat vs carbs. Your body is always burning fat for fuel. It does not make physiological sense that this would stop or slow down this process. So what we end up seeing with increased intensity is a slight increase in fat metabolism, but huge increases in carb metabolism.

Now lower intensity exercise becomes more relevant when you start to consider compliance, endurance level, and people going for distance rather than time.

It’s not really a “myth”, just bad marketing/choice of wording.

All three energy systems are always being utilized, but depending on the intensity of the exercise, one will be the primary energy system while the other two are secondary. For instance, marathon runners (who’s sport is most definitely aerobic in nature, and thus utilizes fat as it’s primary fuel source) need to eat tons of carbohydrates during the week leading up to their event (a practice known as carb loading) to prevent themselves from “hitting the wall” during their race (the point at which the body’s glycogen stores become completely used up and intensity/speed must be significantly decreased in order to finish the race.

I’m on board with the idea that people need high intensity training to get as lean as possible, but not because I don’t think that lower intensity aerobic activity isn’t important or beneficial for fat loss. Higher intensity exercise should be performed to tax the muscular system (aka strength/strength endurance work) and the goal should be to convince the body that it needs muscle to function well. Lower intensity work should be utilized to tax the circulatory system (heart, lungs, and blood vessels), and yes will burn more of a percentage of calories from fat.

In reality they are both important and both serve beneficial functions regarding body composition or performance goals. Trying to discredit or eliminate either is usually not the best course of action.

[quote]Sentoguy wrote:
It’s not really a “myth”, just bad marketing/choice of wording.

All three energy systems are always being utilized, but depending on the intensity of the exercise, one will be the primary energy system while the other two are secondary. For instance, marathon runners (who’s sport is most definitely aerobic in nature, and thus utilizes fat as it’s primary fuel source) need to eat tons of carbohydrates during the week leading up to their event (a practice known as carb loading) to prevent themselves from “hitting the wall” during their race (the point at which the body’s glycogen stores become completely used up and intensity/speed must be significantly decreased in order to finish the race.

I’m on board with the idea that people need high intensity training to get as lean as possible, but not because I don’t think that lower intensity aerobic activity isn’t important or beneficial for fat loss. Higher intensity exercise should be performed to tax the muscular system (aka strength/strength endurance work) and the goal should be to convince the body that it needs muscle to function well. Lower intensity work should be utilized to tax the circulatory system (heart, lungs, and blood vessels), and yes will burn more of a percentage of calories from fat.

In reality they are both important and both serve beneficial functions regarding body composition or performance goals. Trying to discredit or eliminate either is usually not the best course of action.[/quote]

Agree with this. Too many people are too narrow minded and only believe in one approach or the other, when in reality there is benefits to be had from both.

[quote]DAVE101 wrote:
…It does not make physiological sense that this would stop or slow down this process…[/quote]

Can you elaborate on this point please?

[quote]Sentoguy wrote:
It’s not really a “myth”, just bad marketing/choice of wording.

All three energy systems are always being utilized, but depending on the intensity of the exercise, one will be the primary energy system while the other two are secondary. For instance, marathon runners (who’s sport is most definitely aerobic in nature, and thus utilizes fat as it’s primary fuel source) need to eat tons of carbohydrates during the week leading up to their event (a practice known as carb loading) to prevent themselves from “hitting the wall” during their race (the point at which the body’s glycogen stores become completely used up and intensity/speed must be significantly decreased in order to finish the race.

I’m on board with the idea that people need high intensity training to get as lean as possible, but not because I don’t think that lower intensity aerobic activity isn’t important or beneficial for fat loss. Higher intensity exercise should be performed to tax the muscular system (aka strength/strength endurance work) and the goal should be to convince the body that it needs muscle to function well. Lower intensity work should be utilized to tax the circulatory system (heart, lungs, and blood vessels), and yes will burn more of a percentage of calories from fat.

In reality they are both important and both serve beneficial functions regarding body composition or performance goals. Trying to discredit or eliminate either is usually not the best course of action.[/quote]

Don’t marathon runners have specific adaptations (ex: increased HSL, muscle triglycerides etc.) in order to spare that glycogen while they run? It is absolutely correct to say that once the glycogen stored have been depleted the game is pretty much over hence the carb loading, however they will be burning predominantly fat during the race (and relatively more fat than an untrained individual). So in a chronic sense, more fat will be used based on the muscles preference to use it’s TCGs in beta oxidation.

As for the acute response to this “fat burn zone” it really all comes down to the RER. You technically DO burn much more fat during a lower intensity exercise than a higher but NOT for a given amount of time. You would have to exercise longer in order to overcome the high intensity benefits. I guess this would mean that in the end it would all balance out (10 min of high intensity vs 30 min of low intensity…yes these are just numbers i pulled out of my ass).

First, I agree 100% with Sentoguy.

As for this:

[quote]setto222 wrote:
As for the acute response to this “fat burn zone” it really all comes down to the RER. You technically DO burn much more fat during a lower intensity exercise than a higher but NOT for a given amount of time. You would have to exercise longer in order to overcome the high intensity benefits. I guess this would mean that in the end it would all balance out (10 min of high intensity vs 30 min of low intensity…yes these are just numbers i pulled out of my ass). [/quote]

When people say “you only need to work 10 minutes” is that 10 total minutes of WORK or does that include rest intervals? If I’m doing a session of 60 seconds of work followed by 90 seconds of rest or slower-paced work, in order to get 10 total minutes of work I would need to workout for 25 minutes. Still faster than 60 minutes, but longer than “10 minutes.”

You also need to factor in how long can you workout for a given intensity. After about 10 intervals I’m usually done, but I can do some slower-paced work after that.

Finally, you need to consider recovery ability. Takes longer to recover from high-intensity stuff, so you really shouldn’t do it every day. Slower-paced worked, however, can be done daily.

[quote]MikeTheBear wrote:
First, I agree 100% with Sentoguy.

As for this:

[quote]setto222 wrote:
As for the acute response to this “fat burn zone” it really all comes down to the RER. You technically DO burn much more fat during a lower intensity exercise than a higher but NOT for a given amount of time. You would have to exercise longer in order to overcome the high intensity benefits. I guess this would mean that in the end it would all balance out (10 min of high intensity vs 30 min of low intensity…yes these are just numbers i pulled out of my ass). [/quote]

When people say “you only need to work 10 minutes” is that 10 total minutes of WORK or does that include rest intervals? If I’m doing a session of 60 seconds of work followed by 90 seconds of rest or slower-paced work, in order to get 10 total minutes of work I would need to workout for 25 minutes. Still faster than 60 minutes, but longer than “10 minutes.”

You also need to factor in how long can you workout for a given intensity. After about 10 intervals I’m usually done, but I can do some slower-paced work after that.

Finally, you need to consider recovery ability. Takes longer to recover from high-intensity stuff, so you really shouldn’t do it every day. Slower-paced worked, however, can be done daily.
[/quote]

All very valid points :slight_smile:

I would say that the fat burning zone isn’t so much of a myth as it is encouragement that if you don’t want to exercise ball-to-wall you can still burn substantial amounts of fat. But it will take more time per session.

I don’t think many informed people really believe that low intensity cardio is the be all end all to burning away fat (compare somebody who jogs a lot with somebody who sprints a lot, I doubt either would be “fat”).

Believing that either method is the be-all-end-all would be a mistake.

I will say though that the majority of competitive bodybuilders prefer lower intensity longer duration cardio during their contest prep, and they are among the (if not THE) leanest athletes out there as a population. In fairness to high intensity cardio though, they are also eating a SUPER strict clean calorie restricted diet, and are engaging in intense resistance training 4-6 days a week. So replacing low intensity cardio with HIIT would likely push them beyond their recovery limits, likely reduce the productivity of their resistance training workouts, and provide a greater chance for injury (more people tear or pull muscles while using them explosively than using them slowly and steadily).

For someone who isn’t on such an extreme diet and resistance training regimen, HIIT would probably work fine.

I totally agree that both moderate intensity and high intensity have their place. I didn’t even mean to come across as “HIIT > steady state.”

My main take away was: If you’re going to do 30 minutes of cardio, why walk if you can jog? (or walk vs run, or walk vs walk faster, etc). Granted there are times to limit the intensity.

[quote]setto222 wrote:

[quote]DAVE101 wrote:
…It does not make physiological sense that this would stop or slow down this process…[/quote]
Can you elaborate on this point please?[/quote]
It does not make sense to me that, as we work harder and harder, our body would limit one of it’s energy production capacities, aka burning fat for fuel. As intensity increases, carb metabolism increases, but fat metabolism doesn’t have to slow down. It just takes a smaller role when you consider total calories burned.

Where did you get that diagram from?

[quote]DAVE101 wrote:
I totally agree that both moderate intensity and high intensity have their place. I didn’t even mean to come across as “HIIT > steady state.”

My main take away was: If you’re going to do 30 minutes of cardio, why walk if you can jog? (or walk vs run, or walk vs walk faster, etc). Granted there are times to limit the intensity.

[quote]setto222 wrote:

[quote]DAVE101 wrote:
…It does not make physiological sense that this would stop or slow down this process…[/quote]
Can you elaborate on this point please?[/quote]
It does not make sense to me that, as we work harder and harder, our body would limit one of it’s energy production capacities, aka burning fat for fuel. As intensity increases, carb metabolism increases, but fat metabolism doesn’t have to slow down. It just takes a smaller role when you consider total calories burned.[/quote]

I think people are lazy and just look at the percentages to justify a lesser workout (like you said). But this doesn’t really hold true for all conditioning levels or all subjects

ex:
-obese people probably can’t jog for nearly as long as they can walk and therefore would probably burn substantially more calories while walking.
-Fasted state cardio will benefit more from long SS vs higher intensity
etc.
-Untrained individuals would hit their lactic threshold pretty damn easily in a running vs walking scenario

As for your second comment I believe it would come down to metabolic speed. During lower intensities beta oxidation can easily keep up with metabolic demand of the contracting musculature. Blood flow will tend to be moving through periphery and fat stores allowing sufficient circulation of hormone sensitive lipase.

As you move up in intensity, in order to keep up with the metabolic demands, your glycogen is much more readily available. In very high intensities you will often find that your blood will shy away from periphery and the only fat your body will want to metabolize will be intramuscular.

So you are correct that fat utilization does not decrease, but it doesn’t necessarily increase at the same rate as glycogen utilization. Once your glycogen stores are depleted (which would occur faster) you will eventually “hit the wall” and all exercise is over (really over simplified and ignoring gluconeogenesis). So you should be able to exercise for longer and therefore burn more fat at the lower intensity.

All of the above COMPLETELY ignores EPOC and refers to one exercising to failure or for extended periods of time. In a short amount of time, or on a per-minute basis, jogging will just about always be better than running provided your body can handle it.

[quote]setto222 wrote:

[quote]DAVE101 wrote:
I totally agree that both moderate intensity and high intensity have their place. I didn’t even mean to come across as “HIIT > steady state.”

My main take away was: If you’re going to do 30 minutes of cardio, why walk if you can jog? (or walk vs run, or walk vs walk faster, etc). Granted there are times to limit the intensity.

[quote]setto222 wrote:

[quote]DAVE101 wrote:
…It does not make physiological sense that this would stop or slow down this process…[/quote]
Can you elaborate on this point please?[/quote]
It does not make sense to me that, as we work harder and harder, our body would limit one of it’s energy production capacities, aka burning fat for fuel. As intensity increases, carb metabolism increases, but fat metabolism doesn’t have to slow down. It just takes a smaller role when you consider total calories burned.[/quote]

I think people are lazy and just look at the percentages to justify a lesser workout (like you said). But this doesn’t really hold true for all conditioning levels or all subjects

ex:
-obese people probably can’t jog for nearly as long as they can walk and therefore would probably burn substantially more calories while walking.
-Fasted state cardio will benefit more from long SS vs higher intensity
etc.
-Untrained individuals would hit their lactic threshold pretty damn easily in a running vs walking scenario

As for your second comment I believe it would come down to metabolic speed. During lower intensities beta oxidation can easily keep up with metabolic demand of the contracting musculature. Blood flow will tend to be moving through periphery and fat stores allowing sufficient circulation of hormone sensitive lipase.

As you move up in intensity, in order to keep up with the metabolic demands, your glycogen is much more readily available. In very high intensities you will often find that your blood will shy away from periphery and the only fat your body will want to metabolize will be intramuscular.

So you are correct that fat utilization does not decrease, but it doesn’t necessarily increase at the same rate as glycogen utilization. Once your glycogen stores are depleted (which would occur faster) you will eventually “hit the wall” and all exercise is over (really over simplified and ignoring gluconeogenesis). So you should be able to exercise for longer and therefore burn more fat at the lower intensity.

All of the above COMPLETELY ignores EPOC and refers to one exercising to failure or for extended periods of time. In a short amount of time, or on a per-minute basis, jogging will just about always be better than running provided your body can handle it.

[/quote]

Wasn’t EPOC overrated? I read this somewhere here…

[quote]Carnage wrote:

[quote]setto222 wrote:

[quote]DAVE101 wrote:
I totally agree that both moderate intensity and high intensity have their place. I didn’t even mean to come across as “HIIT > steady state.”

My main take away was: If you’re going to do 30 minutes of cardio, why walk if you can jog? (or walk vs run, or walk vs walk faster, etc). Granted there are times to limit the intensity.

[quote]setto222 wrote:

[quote]DAVE101 wrote:
…It does not make physiological sense that this would stop or slow down this process…[/quote]
Can you elaborate on this point please?[/quote]
It does not make sense to me that, as we work harder and harder, our body would limit one of it’s energy production capacities, aka burning fat for fuel. As intensity increases, carb metabolism increases, but fat metabolism doesn’t have to slow down. It just takes a smaller role when you consider total calories burned.[/quote]

I think people are lazy and just look at the percentages to justify a lesser workout (like you said). But this doesn’t really hold true for all conditioning levels or all subjects

ex:
-obese people probably can’t jog for nearly as long as they can walk and therefore would probably burn substantially more calories while walking.
-Fasted state cardio will benefit more from long SS vs higher intensity
etc.
-Untrained individuals would hit their lactic threshold pretty damn easily in a running vs walking scenario

As for your second comment I believe it would come down to metabolic speed. During lower intensities beta oxidation can easily keep up with metabolic demand of the contracting musculature. Blood flow will tend to be moving through periphery and fat stores allowing sufficient circulation of hormone sensitive lipase.

As you move up in intensity, in order to keep up with the metabolic demands, your glycogen is much more readily available. In very high intensities you will often find that your blood will shy away from periphery and the only fat your body will want to metabolize will be intramuscular.

So you are correct that fat utilization does not decrease, but it doesn’t necessarily increase at the same rate as glycogen utilization. Once your glycogen stores are depleted (which would occur faster) you will eventually “hit the wall” and all exercise is over (really over simplified and ignoring gluconeogenesis). So you should be able to exercise for longer and therefore burn more fat at the lower intensity.

All of the above COMPLETELY ignores EPOC and refers to one exercising to failure or for extended periods of time. In a short amount of time, or on a per-minute basis, jogging will just about always be better than running provided your body can handle it.

[/quote]

Wasn’t EPOC overrated? I read this somewhere here…[/quote]

Never read anything like that. Would love to see where you read that?

One theory concerning EPOC was dispoved (by Brooks et al iirc) which suggested that the highter EPOC of HIIT was due to metabolism replenishing glycogen as well as clearing lactate. But that doesn’t change the large amount of recovery VO2 from HIIT compared to SS

As Meb Keflezighi’s (4th Place London Olympics) training assistant and massage/stretch therapist for the last 5 years, I can honestly say this is one of the most informative and competent threads I have come across in a loonngg ass time.

I was also with the 1996 US Olympic Sculling team and got to train with them and watch them for a six month period.

What I came away with was this. Both Coaches, Igor Grinko ('96 sculling team) and Bob Larson (Ucla, Meb’s personal coach of 17 years) both understood/ understand that If on a limited time schedule you are better off
to Train at a Maximum heart rate for as long as possible than to train steady state.

There analogy is the gas in the tank. You only have so much to burn so burn it with maximum output. It has also been found to be true that output of heartrate above 85% will transfer over into endurance while the opposite is Not true.

As American Alpinist Marc Twight once famously said “You always have sometime to burn, even if it is Grey Matter”.

Your body can only produce so much ATP at a time at the anaerobic level but has a near unlimited capacity to produce this at a lower heart rate level.

When Meb is two weeks out from a major Marathon he is doing a LOT more speed work twice a week while doing his long runs 22+ miles at a more moderate level AND usually on An Egg, a sausage and a piece of toast. To say he is lean would make John Meadows look fat…no offence to John.

Lets please keep this thread going in this positive direction…killerDIRK.

Im the one on the bike, Ha ha…http://www.youtube.com/watch?v=_P1Y6b1RXM0

[quote]killerDIRK wrote:
As Meb Keflezighi’s (4th Place London Olympics) training assistant and massage/stretch therapist for the last 5 years, I can honestly say this is one of the most informative and competent threads I have come across in a loonngg ass time.

I was also with the 1996 US Olympic Sculling team and got to train with them and watch them for a six month period.

What I came away with was this. Both Coaches, Igor Grinko ('96 sculling team) and Bob Larson (Ucla, Meb’s personal coach of 17 years) both understood/ understand that If on a limited time schedule you are better off
to Train at a Maximum heart rate for as long as possible than to train steady state.

There analogy is the gas in the tank. You only have so much to burn so burn it with maximum output. It has also been found to be true that output of heartrate above 85% will transfer over into endurance while the opposite is Not true.

As American Alpinist Marc Twight once famously said “You always have sometime to burn, even if it is Grey Matter”.

Your body can only produce so much ATP at a time at the anaerobic level but has a near unlimited capacity to produce this at a lower heart rate level.

When Meb is two weeks out from a major Marathon he is doing a LOT more speed work twice a week while doing his long runs 22+ miles at a more moderate level AND usually on An Egg, a sausage and a piece of toast. To say he is lean would make John Meadows look fat…no offence to John.

Lets please keep this thread going in this positive direction…killerDIRK.

Im the one on the bike, Ha ha…http://www.youtube.com/watch?v=_P1Y6b1RXM0[/quote]

Yeah if you are only going to have 3 hours a week to train then higher intensity training is going to give you more bang for your buck. But if you have more resources in terms of time available, you would probably be better served with training modalities that more specifically illicit your desired training response (be that improved leanness, speed, strength, etc…).

To compare it to diet, a bodybuilder could potentially just eat quinoa with some olive oil on it (since quinoa is technically a complete protein, as well as a complex carb, and the olive oil would provide EFA’s) morning noon and night and probably be at least fairly healthy (would probably need to take a multivitamin as well). Probably more heathy than one who only are Chicken or one who only ate grapefruit, but eating a diet consisting of a variety of foods, specifically chosen to satisfy specific nutritional needs, is probably going to yield better results.

Not saying that you are saying otherwise; you even mentioned how Meb (a competitive marathoner) did some speed work during his race prep. Just saying that a lot of people (coaches included) tend to get hung up on one type of cardio or another and some even seek to discredit the other type.

In regards to the discussion on EPOC, my understanding has always been that it was believed that the body increased it’s metabolic and cardio respiratory rate to make up for the “oxygen debt” it had incurred during the intense exercise. But really, all that matters from a fat loss perspective is that we know the body DOES increase it’s metabolic rate post intense exercise. This is also true of pure resistance training (provided it is actually intense in nature) as well though and not unique to only HIIT sessions.

Not saying that you are saying otherwise; you even mentioned how Meb (a competitive marathoner) did some speed work during his race prep. Just saying that a lot of people (coaches included) tend to get hung up on one type of cardio or another and some even seek to discredit the other type.

And this is the problem some people have with the “blind” following that crapfat(crossfit) has seemed to generate. People do not do their homework OR are just looking for the latest and greatest and getting nowhere.

What happened, in this case, to sticking with the solid basics: Squat Bench Deadlift Overhead Press et all ?

Your last paragraph has been a proven scientific priciple for along time now. We do know that either strength training or cardio will raise ones resting metabolism for a period of up to 48 hours post training session.

As far as food consumption I could not live off of only chicken, brocc and rice. I would go nuts…mmm nuts ; )

Anyway…all valid points to this point !

[quote]killerDIRK wrote:
And this is the problem some people have with the “blind” following that crapfat(crossfit) has seemed to generate. People do not do their homework OR are just looking for the latest and greatest and getting nowhere.
[/quote]

Yeah, I’d like to join you in the CF bashing, but I’ll refrain from going down the negativity or name calling road. After all, for all it’s shortcomings, it is at least getting people active and motivated to improve their bodies, so it’s not all bad.

[quote]
What happened, in this case, to sticking with the solid basics: Squat Bench Deadlift Overhead Press et all ?

Your last paragraph has been a proven scientific priciple for along time now. We do know that either strength training or cardio will raise ones resting metabolism for a period of up to 48 hours post training session.

As far as food consumption I could not live off of only chicken, brocc and rice. I would go nuts…mmm nuts ; )

Anyway…all valid points to this point ![/quote]

Yeah, totally agree. And lol a out the food variety comment. Not only are most people like you in that regard, but eating a more varied diet is actually healthier for you as well. Even physique athletes who eat super strict, very limited food choice diets only do so for short periods of time and for very specific reasons.

Thanks for the additions to the thread, and really cool that you get the chance to work with Oly athletes.

Thanks Bro. Even though I have been an Endurance Athlete my entire life, I do the Heavy lifting of Squat, Bench, Deadlift per Louie Simmons westside template (Heavy and dynamic) for the months of Nov-Feb and then transition into more of the 3-5sets of 25 reps for the same movements in season.

It has kept my strong during the winter and injury free, then lite and quick during the GO months…

[quote]Sentoguy wrote:
Believing that either method is the be-all-end-all would be a mistake.

I will say though that the majority of competitive bodybuilders prefer lower intensity longer duration cardio during their contest prep, and they are among the (if not THE) leanest athletes out there as a population. In fairness to high intensity cardio though, they are also eating a SUPER strict clean calorie restricted diet, and are engaging in intense resistance training 4-6 days a week.
[/quote]

Also I would like to point out that the kind of weight training many bodybuilders use during contest prep is, in itself, very similar to HIIT–lactic acid training with incomplete rest periods. While I do not believe the same will hold true for say…bicep curls…nobody can tell me that leg supersets with no rest do not constitute HIIT style training. If you do, I will respond that you have obviously never trained with enough intensity to squat properly :). All one needs to do is look at the kind of training Tate and Meadows get into on their Saturday leg-fests. The work:rest ratio is definitely high enough to qualify as is the proportional amount of muscle mass in action during work periods.

So, in essence, many bodybuilders are already doing HIIT style work during their weight training regimens in contest prep. Viewed from this angle I can say it is much less surprising that many prefer low intensity cardio.

[quote]killerDIRK wrote:

There analogy is the gas in the tank. You only have so much to burn so burn it with maximum output. It has also been found to be true that output of heartrate above 85% will transfer over into endurance while the opposite is Not true.

[/quote]

Good post. Where can I find the source for this? I have somebody I might want to show it to…