The fat burning zone

[lylemcd]

A question that comes up very often is akin to the following

I think someone mentioned, Lyle?, that there really is no fat burning zone for things like cardio....

Not sure...but I guess we all burn calories during aerobic or anaeorbic exercise....the question becomes how much?

But I always figured the harder I work out the more bang for my buck....but then I saw a post (I hope this is not out of context) in which Lyle states:

"fat cannot be oxidized under anaerobic conditions"

This got me thinking about my "pushing my limits" when I do cardio and trying to get into the anaerobic state (i.e. about 85% maxHR)...and perhaps this is why I am having problems targeting my FAT vs. anything else??? Is that why some refer to the "fat burning zone?" as generally slower than anerobic...in other words..the aerobic only rate? If FAT cannot be oxidized under anaeorbic conditions...what is my body burning when I'm in the anaerobic state of cardio exercise?

Okay..I know I'm an idiot...I'm still learning...so can you explain in simple terms?

My answer:
Simplistically
As you move from lwo intensities to higher intensities, the amount of fat vs. carbs burned shifts from one to the other

At low intensities, you may burn near 100% fat
At the highest intensiy (acually just about anything above lactate threshold), you burn 100% carbs

at any intensity between, you burn a proportion of the two. As you move from lower to high intensity, you burn proportionally less fat and proportinally more carbs until you reach a point taht the body can only burn carbs.

The issue with the 'fat burning zone' concept is that people confuse %ages with absolutes

Say you're walking at 3mph and burning 5 cal/min, but you're burning 100% fat. That's 5 cal/min of fat.

Say you're running at 6 mph and burning 10 cal/min but you're burning 50% fat.

Ruh roh, that's less fat, isn't it? No, it's not. 10 cal/min * 50% 5 cal/min of fat. It's the same amount of fat in absolute terms although it's a lower percentage. But you're also burning 5 cal/min of carbohydrates.

Say that at 6 mph you're burning 10 cal/min but still 65% fat. That's still lower by %age than at 3mph. But yo'ure burning 6.5 cal/min of fat which is higher. And you burn more total calories. And you deplete some of the carbohdyrate in your muscle.

Some studies have shown that that maximum absolute amount of fat burned occurs right around the lactat tehreshold (the highest, hardest, most painful intensity that you can sustain for an extended period) although it depends on training status and some other factors

When you deplete muscle glycogen (via burning it during exercise and/or carbohdyrate restriction), this increases whole body fat oxidation. And, for the most part, what you burn during exercise is less relevant than than what you burn the rest of the day and none of this matters if you aren't in a deficit). So say you do a hard session where you burn a combination of fat and carbs. Not only did you burn those calories, by depleting muscle glycogen

a. your body will burn more fat for the rest of the day (I'm not saying more in terms of 'metabolic rate' is increases, but more in terms of the proportions used)
b. incoming carbohdyrates tend to go to refilling muscle glycogen instead of being used for energy

Which is why, to a certain degree, it doesn't matter what you do as long as the calorie burn is roughly similar

Low intensity activity is sort of a direct fat burner, you burn mostly fat for fuel but that's all you get out of it.

Higher intensity burns some proportion of fat/carbs but impacts more greatly on what you burn later in the day

Intervals burn only carbs during training but the glycogen depletion and other factors may make you burn more fat later in the day

I think the bigger issue is that, if you do too much high intensity activity too frequently, you get overtrained and that causes too many problems.

Elite athletes do 75% or more of their volumes at low intensities, what makes fitness people think that they can handle more than this?

[jw8725]

Hello Lyle,

Just joined up, this is my maiden post here. With respect to your above post. How do you rate HIIT?

Thanks

update:
ah ha! Have now stumbled across the other sticky. Loving the wealth of information here. About to buy your protein book!

[lylemcd]

read the blog

I started examining the issue of steady state vs. intervals about a week ago and have a least another week of posts to make about it

[DannyN]

Lyle what do you think of programs that are claimed to be more effective at burning fat by using only high intensity cardio like stairs exercises, up hill running, rope jumping, sprints using the rationale that they raise EPOC?

[Nigeepoo]

Isn't that question answered here?

[DannyN]

Originally Posted by Nigeepoo

Isn't that question answered here?

I don't think so. The high intensity cardio I was talking about is not based on specific intervals, it's just high intensity.

[Nigeepoo]

Originally Posted by DannyN

I don't think so. The high intensity cardio I was talking about is not based on specific intervals, it's just high intensity.

High intensity cardio cannot be maintained for very long. Therefore, it's effectively done in intervals.

[faz]

Originally Posted by DannyN

I don't think so. The high intensity cardio I was talking about is not based on specific intervals, it's just high intensity.

do you mean say running for 30mins at a higher intensity(rather than jogging) compared to intervals.

most of the studies like tabata etc seem to be HIIT versus low-intensity,i have always wondered if it was HIIT versus medium to higher intensities would the results be a lot different.

[lylemcd]

Originally Posted by DannyN

Lyle what do you think of programs that are claimed to be more effective at burning fat by using only high intensity cardio like stairs exercises, up hill running, rope jumping, sprints using the rationale that they raise EPOC?

READ THE BLOG

[DannyN]

Is there any truth to the claim (made by steady cardio fans) that high intensity cardio is more catabolic and a natural would lose lot of muscles not just fat?

I have also heard the opposite claim. That steady cardio is more catabolic and high intensity cardio less. They use the example of the physique difference between the sprinter and the marathoner (both not lifting weights) but one being more skinny as having less muscles.