Other/Mixed Why you don't burn much fat during HIT, and why it does not matter

[conor78]

@mprevost
Do use battle ropes or prowler sleds? The gym I use has them and I use them at end of my training. Generally load the prowler with 50kg and push 20 yards up 20 yards back. Rest till heart rate drops below 140 and go again for another 4 repeats. With the battle ropes I go for about 15 seconds and then rest til heart rate gives below 140...
I used to use what I thought were tabatas but your post has confirmed they were something else entirely..

 

[mprevost]

@mprevost
Do use battle ropes or prowler sleds? The gym I use has them and I use them at end of my training. Generally load the prowler with 50kg and push 20 yards up 20 yards back. Rest till heart rate drops below 140 and go again for another 4 repeats. With the battle ropes I go for about 15 seconds and then rest til heart rate gives below 140...
I used to use what I thought were tabatas but your post has confirmed they were something else entirely..

Not currently using anything like that because I don't have access. But I have. Love the prowler.

 

[mprevost]

Oh OK so not really anything they were doing in the study. More like what we do with A+A.

Yes, probably, though I have not read the A + A stuff.

 

[North Coast Miller]

As exercise intensity increases, you release more "fight or flight" and catabolic hormones. Insulin production decreases but many other hormones increase. Note that HIT is performed at or near 100% VO2 max typically.
View attachment 4374
Epinehprine is a strong activator of hormone sensitive lipase, which is the enzyme in the adipocyte (fat cell) that breaks down triglycerides into fatty acids and glycerol. So....you would think that at higher exercise intensities that the proportion of fat burned would increase. However, this is not the case. See below:
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So, why this paradox? It turns out that lactate and hydrogen ions play a key role in suppressing fat oxidation. Hydrogen ions inhibit hormone sensitive lipase and lactate stimulates the resynthesis of fatty acids. Therefore, even though high intensity exercise increases epinephrine production (a stimulator of hormone sensitive lipase), fat oxidation is reduced. But here is why it does not matter. The higher the intensity of exercise, the greater the shift in respiratory exchange ratio (R) after the exercise session. R is a measure that tells us what fuel we are using. See below:
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What we see is after high intensity exercise, there is a prolonged shift (up to 48 hours!) towards a lower R, which means more fat oxidation during recovery, after exercise, even though you burned little during exercise.

Question about the second graph showing decreasing % of fat contribution as VO2 approaches top-end. While the percentage contribution is dropping, the contribution in terms of total calories broken down for ATP recharge has to be increasing as the total demand for fat and carb/per unit of time goes through the ceiling.

Is there a break point where the decreasing % contribution and increasing quantity balance out or drop off, leading to an actual decrease in total fat used for energy?

I ask, as I've read other research that showed the same trend but also claimed the total fat burned is higher anyway per unit of time than what would have been burned at a lower intensity/higher % contribution - you're burning more fat anyway for a given time frame, but burning a much larger amount of carbs as well.


Here's a chart from a paper I saved, looks like the break point is (or used to be understood to be) about 65% Vo2

here's another showing a different breakdown contribution over time:

 

[North Coast Miller]

@mprevost Can you elaborate more on the role of hormones during recovery? The higher intensity I train, I seem to be able to recover better/faster after a while. However, when I train at lower intensities, it seems my ability to recover gets worse over time.

I find this as well. Is self-reinforcing up to a point where I will start to feel some burn-out, but the lower intensity I train, the less I retain ability to do so. It holds out for a few and doesn't seem to be related at all to overall aerobic fitness.

I have read some research that showed fat processing in mitochondria was relatively steady state based on mitochondrial density, while pyruvate throughput increases or decreases with intensity range - repeated training at higher intensity improving the rate of the reaction as much as 15% or more compared to controls who only trained at lower intensities...IIRC? Been a few since I read that.

Anecdotally I find it to be true, but the research didn't go into details of how durable the adaptation might be. For me about 2 weeks.

 

[Steve Freides]

The higher intensity I train, I seem to be able to recover better/faster after a while. However, when I train at lower intensities, it seems my ability to recover gets worse over time.

Interesting that a number of folks are getting good results by combining higher intensity A + A training (w/ kettlebells swings and/or snatches) with LSD running or cycling (lower intensity). It sounds like a very good combination to me.

-S-

 

[Deleted member 5559]

Interesting that a number of folks are getting good results by combining higher intensity A + A training (w/ kettlebells swings and/or snatches) with LSD running or cycling (lower intensity).

By lower intensities I should say lower training volume load or whatever the technical term might be. I think where I'm seeing issues is with a training volume load that does not induce enough fatigue to force supercompensation or makes that window on the SRA curve too small that I cannot hit it right and experiencing involution. The training volume load of the A+A protocols seem to be fatiguing enough to create a larger supercompensation window from the experimenting I've done of it.

 

[mprevost]

Is there a break point where the decreasing % contribution and increasing quantity balance out or drop off, leading to an actual decrease in total fat used for energy?



Here's a chart from a paper I saved, looks like the break point is (or used to be understood to be) about 65% Vo2

here's another showing a different breakdown contribution over time:

For sure. 65% VO2 max is about right. It will vary somewhat though. 65% VO2 max is a pretty light intensity, certainly well below the intensity used in any HIT protocol.

 

[mprevost]

Interesting that a number of folks are getting good results by combining higher intensity A + A training (w/ kettlebells swings and/or snatches) with LSD running or cycling (lower intensity). It sounds like a very good combination to me.

-S-

Me too! Some basic strength work, a sprinkling of high intensity work (just a little), a bit of mobility and some easy paced steady state cardio (even walking) is a recipe for a healthy life.