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

[mprevost]

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.

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:

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:

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.

 

[Michael Scott]

Wow, that is interesting information....truly interesting. Especially when you expect the reverse to be the case. Thank you for sharing this information.

 

[Deleted member 5559]

@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.

 

[Anna C]

which means more fat oxidation during recovery, after exercise, even though you burned little during exercise

@mprevost Can you clarify the use of "more" in this sentence? I can think of 3 possible meanings, just want to understand which it is (or more than one):

1) total fat oxidation of (HITT-after) is greater than (HITT-during)

2) In comparison to an aerobic session of the same duration, total fat oxidation of (HITT-during + HITT-after) is greater than (aerobic-during + aerobic-after)

3) In comparison to an aerobic session of the same caloric expenditure (where presumably the aerobic session would be longer in duration), total fat oxidation of (HITT-during + HITT-after) is greater than (aerobic-during + aerobic-after)

By "aerobic" I mean MAF HR running, rowing, etc.

Thanks

 

[wespom9]

Here is a question, one I often struggle with: with all those other hormonal things that happen (for better or worse, I hesitate to say it leans more toward worse) is it *worth it* to do HIIT? Is it worth it 1x week? 2x? at what point does it become too much? Is not doing any at all a hindrance?

 

[pet']

Hello,

Is not it about the fact that HIT creates a oxygen deficit

Kind regards,

Pet'

 

[Waffles03]

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.

Does this mean you can combine the two (HIIT and LISS) by doing HIIT first and then follow up by doing LISS cardio to burn more fat?

 

[Deleted member 5559]

Does this mean you can combine the two (HIIT and LISS) by doing HIIT first and then follow up by doing LISS cardio to burn more fat?

I think studies have been done that show the opposite of this. Better to train aerobic cardio first and HITT or strength training after or better yet in a different training session later in the day.

 

[Steve Freides]

My experience has been that you do what matters most to you first. The only reason to break that rule is if you can really separate your multiple training sessions by long enough to completely recover. Most non-professional athletes have trouble finding that kind of time (more than one exercise time) in their day.

-S-

 

[mprevost]

@mprevost Can you clarify the use of "more" in this sentence? I can think of 3 possible meanings, just want to understand which it is (or more than one):

1) total fat oxidation of (HITT-after) is greater than (HITT-during)

2) In comparison to an aerobic session of the same duration, total fat oxidation of (HITT-during + HITT-after) is greater than (aerobic-during + aerobic-after)

3) In comparison to an aerobic session of the same caloric expenditure (where presumably the aerobic session would be longer in duration), total fat oxidation of (HITT-during + HITT-after) is greater than (aerobic-during + aerobic-after)

By "aerobic" I mean MAF HR running, rowing, etc.

Thanks

More = more after the fact than during the exercise session. Also, what I mean by more is that you can burn quite a few calories from fat after a training session, more than we used to think. One particular study found an extra 500 kcals burned in the 48 hours after a training session. They used heavy barbell training and rest pause sets. We used to think that the "after burn" was only 30 kcals or so. The after burn effect depends on both intensity and duration. But a third factor, that has not really been measured and is often not discussed is the energy required for repair and remodeling of tissue. I think that is a pretty significant one for heavy barbell training and the associated after burn efffects. So the increased caloric expenditure following activity depends on duration, intensity, and need for repair. It just so happens that the highest after burn effect I have seen in the literature was the 500 kcals after heavy barbell training using rest pause sets. I don't know if other types of exercise can surpass that but I suspect that the energy cost of repair was the primary cause in this case. Consider that high intensity bike intervals, which can produce higher lactate levels than barbell training, don't typically produce that much after burn effects.

But to put it all in perspective, I still firmly believe that training is for fitness and nutrition is for weight loss. The best reasons to do or not to do HIT training have little to do with weight loss and more to do with the type of fitness you are trying to produce or the time that you have available to train.

Hope that answers your questions.

 

[mprevost]

@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.

Not sure exactly what question you are asking. Recovery cost is a factor of both volume and intensity. It is easy to overdo it with volume because acutely the training session feels OK because the intensity is moderate, but the full implications of the volume are not realized until after. High intensity is more self limiting during the execution of the workout itself.

 

[mprevost]

Does this mean you can combine the two (HIIT and LISS) by doing HIIT first and then follow up by doing LISS cardio to burn more fat?

I am not aware of any data showing that preceding a longer, moderate/easy paced workout with a HIT session can shift the fuel burn ratio in favor of fat burning. It is more likely that the hydrogen ion and lactate load would be cleared quickly during the longer, easier effort, resulting in little or no impact.

 

[mprevost]

Hello,

Is not it about the fact that HIT creates a oxygen deficit

Kind regards,

Pet'

Yes, that is what is measured to determine the extra calorie cost. It is called the excess post exercise oxygen consumption (EPOC). We used to call it oxygen debt but EPOC is more correct because some of the extra oxygen cost is due to factors other than oxygen debt (like recovery, increased body temperature etc.). When you have a big, long lasting EPOC, oxygen consumption is elevated and R shifts to a lower value.

 

[mprevost]

Here is a data graph from the study. This is a comparison of traditional weight training vs rest pause type of training (go to failure, rest 20 seconds, do 2-3 more reps, rest 20 seconds, do 2-3 more reps.

Note that there was an increase in REE for both groups but it was much higher for rest/pause. Also, the decline in R was significant for rest pause, indicating a shift towards burning fat at rest. This is data from 22 hours post training compared to pre-training.

 

[mprevost]

Here is a question, one I often struggle with: with all those other hormonal things that happen (for better or worse, I hesitate to say it leans more toward worse) is it *worth it* to do HIIT? Is it worth it 1x week? 2x? at what point does it become too much? Is not doing any at all a hindrance?

It depends on what you are training for and how much time you have. I am simply training for health and life.

*If I had only 10 minutes, 3 times per week to train (30 min total) I would do HIT

*If I had one hour, 3 times per week to train (3 hours total) I would do basic strength training with a dash of HIT at the end of each session.

*If I had one hour per day to train, I would do basic strength training (3 X week) , MAF style aerobic training (3 X week), and a small (once per week) bit of HIT.

*If I had more time than that, I would do the last choice above and add in lots of walking and nap every day. I currently have lots of time ; )

Mike

 

[Antti]

It depends on what you are training for and how much time you have. I am simply training for health and life.

*If I had only 10 minutes, 3 times per week to train (30 min total) I would do HIT

*If I had one hour, 3 times per week to train (3 hours total) I would do basic strength training with a dash of HIT at the end of each session.

*If I had one hour per day to train, I would do basic strength training (3 X week) , MAF style aerobic training (3 X week), and a small (once per week) bit of HIT.

*If I had more time than that, I would do the last choice above and add in lots of walking and nap every day. I currently have lots of time ; )

Mike

Mike , thank you for sharing your insight.

Do you think that your example of training should be different between different stages of age and development, if we take the goal to be the same?

The reason I ask is that it is typically thought that strength and muscle mass are hard to come by but stick around, while endurance is easy come, easy go. It is also generally accepted that the strength and hypertrophy training is easier or the progress in them faster when one is young. So, should one concentrate more on strength or hypertrophy while younger to reap the benefits of faster progress? Or is it the other way round, that one should strength train more in the old age to keep onto the muscle and strength better?

I do understand that cardio has health benefits and not just the endurance aspect which makes sports and everyday life easier. Do you think there's a certain time in our lives when we should increase our cardio training for the sake of life expectancy and health?

 

[mprevost]

Mike , thank you for sharing your insight.

Do you think that your example of training should be different between different stages of age and development, if we take the goal to be the same?

The reason I ask is that it is typically thought that strength and muscle mass are hard to come by but stick around, while endurance is easy come, easy go. It is also generally accepted that the strength and hypertrophy training is easier or the progress in them faster when one is young. So, should one concentrate more on strength or hypertrophy while younger to reap the benefits of faster progress? Or is it the other way round, that one should strength train more in the old age to keep onto the muscle and strength better?

I do understand that cardio has health benefits and not just the endurance aspect which makes sports and everyday life easier. Do you think there's a certain time in our lives when we should increase our cardio training for the sake of life expectancy and health?

As a young person, you can still afford to put most emphasis on performance and appearance. This is because you have not done too much damage to your health yet. As you get older, and I am 50, your priorities tend to change, and you have accumulated lots of damage, even if you have lived an exceptionally "pure" life. The most powerful predictor of cardiovascular mortality, by far, is age. We will all get old if we are lucky because it beats the alternative. I think it is OK to still prioritize performance/appearance as you get older but you have to have a realistic appraisal of risk vs rewards and be realistic about what you want. I met a guy in the gym who was in his 60s, who could still bench press 300+ but he continued to supplement with protein and BCAAs despite the fact that he was pissing blood, had kidney damage (not due to high protein) and his doctor warned him that the excess protein was causing more damage. He could not let go of his big bench press or his muscles. That was 5 years ago, he may be dead now. I would have prioritized differently.

I feel like as a young person you can train for performance but should always keep an eye on health.

As an older person, you should train for health, but keep an eye on performance. As you get older, health is going to limit performance, so downplaying that part of your training will compromise both.

Having said all of that, if you don't have lots of muscle in your 30s, you are not likely to develop it in your 50s (except for a gifted few), so if your goal is to have a big, muscular physique, better get after it young, but don't neglect health.

 

[Antti]

As a young person, you can still afford to put most emphasis on performance and appearance. This is because you have not done too much damage to your health yet. As you get older, and I am 50, your priorities tend to change, and you have accumulated lots of damage, even if you have lived an exceptionally "pure" life. The most powerful predictor of cardiovascular mortality, by far, is age. We will all get old if we are lucky because it beats the alternative. I think it is OK to still prioritize performance/appearance as you get older but you have to have a realistic appraisal of risk vs rewards and be realistic about what you want. I met a guy in the gym who was in his 60s, who could still bench press 300+ but he continued to supplement with protein and BCAAs despite the fact that he was pissing blood, had kidney damage (not due to high protein) and his doctor warned him that the excess protein was causing more damage. He could not let go of his big bench press or his muscles. That was 5 years ago, he may be dead now. I would have prioritized differently.

I feel like as a young person you can train for performance but should always keep an eye on health.

As an older person, you should train for health, but keep an eye on performance. As you get older, health is going to limit performance, so downplaying that part of your training will compromise both.

Having said all of that, if you don't have lots of muscle in your 30s, you are not likely to develop it in your 50s (except for a gifted few), so if your goal is to have a big, muscular physique, better get after it young, but don't neglect health.

Do you think that muscle mass has a say in life expectancy? I've seen studies where grip strength or muscle mass have correlated with life expectancy. I can understand that these are flawed assumptions, as that grip strength, for example, is easily chosen because of the ease of testing, and that the muscle mass may just indicate a lack of illness that would cause muscle loss. But what is your opinion with it?

 

[mprevost]

Do you think that muscle mass has a say in life expectancy? I've seen studies where grip strength or muscle mass have correlated with life expectancy. I can understand that these are flawed assumptions, as that grip strength, for example, is easily chosen because of the ease of testing, and that the muscle mass may just indicate a lack of illness that would cause muscle loss. But what is your opinion with it?

Hard to say. I can see increased muscle mass assisting with glucose disposal and therefore blood glucose control. Plus more muscle mass would allow you to move more and expend more calories. But those are speculations. As you identified, the correlations only suggest a relationship but the direction of causality can't be determined (i.e., do healthier people have greater grip strength or does greater grip strength lead to better health). I think the best reason to have more muscle mass is to preserve functional capacity so you can remain independent and do the stuff you love for longer.

 

[Steve Freides]

IMHO, it’s tough to beat lots of walking combined with either a barbell deadlift or a kettlebell swing or snatch. It can literally be 10 minutes of lifting weights every day plus walking.

-S-