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

[ali]

I currently have lots of time ; )

And all the better we are for that! Lots of morsels in there to chew over.
Hoping that you could answer a couple of related questions Mike, please?

Is there a difference in energy usage comparing aerobic and anaerobic substrates? So at high and very high intensities the anaerobic system is ripping up the glucose.....does that imply that the revved up aerobic system is preferentially using pyruvate for the Krebs cycle?
At the 40% VO2 Max point on the graph, fat and carbs are equal, as intensity increases, energy is supplied more by carbs.....is that due to more anaerobic influence or due to more glucose being made available for use and thus will be used aerobically too? That glucose being made available by the dump of hormones, ready for action.
It's known that trained endurance athletes can utilise more fat at higher intensities than those untrained, or less trained, so the implication of that is fat is being used in the Krebs cycle whilst additional anaerobic input supplied by glucose and an efficient lactate shuttle. I get that. But when carb usage is so high, those carbs must also being burned for mitochondrial ATP too, at some point?
So if looking to be metabolically flexible.....being able to switch aerobic fuel to and from carbs to fat and vice versa.....can this switch occur quickly or is it due to the duration and intensity? Can both pyruvate and fatty acids be prepped to enter the Krebs cycle at the same time?
Hope I'm making sort sort of sense to you....many thanks

 

[mprevost]

The answer to your last question is YES, fats are almost always burned along with pyruvate from glycolysis (in the same cell and same mitochondria). Carbs and fats are both being pushed through the krebs cycle and burned aerobically. At high intensities the krebs cycle and oxidative phosphorylation cannot keep up with ATP demand so they get kinda backed up (not technically correct but it gets complex) so pyruvate builds up and it is transformed to lactate and shuttled out of the muscle. This is an oversimplification but it works conceptually (in reality lactate production has to do with REDOX potential).

 

[mprevost]

Would it help if I did a new post on why we produce lactate?

 

[Waffles03]

Would it help if I did a new post on why we produce lactate?

It would definitely be interesting.

 

[ali]

The answer to your last question is YES, fats are almost always burned along with pyruvate from glycolysis (in the same cell and same mitochondria).

My saviour! Thank you.

 

[ali]

Just to follow up there Mike.......acetyl coA can be sourced from pyruvate and fatty acids with enzymes for each operating at the same time. And all this is driven by cellular energy status. At rest or at low intensity, cellular energy is on idle, mostly, although not always, using fatty acid. As Intensity increases, other energy sources are mobilised and depending on that intensity and training history, presumably genetics and diet too, then the cell selects whatever energy is there to get the job done.
I had thought that fuel selected for aerobic use had to have separate enzymatic processes that couldn't run alongside each other, it was one or the other. And that confused me and you know I couldn't find an answer anywhere.....at least one that I could understand. So thanks for clearing that up. Hope you get the opportunity for some time to be outside today. Cheers.

 

[elli]

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.

Tip: Do HIIT Followed by Steady-State Cardio | T Nation
Although this might not be the most scientific source ...
I would totally contradict to what you stated, at least according to the first part.
You need full power for hiit, why pre-exhaust with LISS when you feel fresh and ready to go all out? Short warm up and off you go. Cool down with cardio. Or do it the next day for recovery.

 

[mprevost]

Tip: Do HIIT Followed by Steady-State Cardio | T Nation
Although this might not be the most scientific source ...
I would totally contradict to what you stated, at least according to the first part.
You need full power for hiit, why pre-exhaust with LISS when you feel fresh and ready to go all out? Short warm up and off you go. Cool down with cardio. Or do it the next day for recovery.

Well....he is completely wrong. A quick peek at any undergraduate exercise physiology textbook would clear up his misunderstandings.

 

[Deleted member 5559]

I believe the research from the study I read was more about combining fitness attributes in a single workout. The conclusion was that performing endurance and strength in the same cycle actually prevented improvement in either. One of the outcomes they found was that improving the body's ability to burn fat was better with low intensity cardio in the AM in a fasted state. Additionally, if wanting to improve strength at the same time, one should train strength >12 hours later in a separate session.

 

[elli]

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-

That was the answer to your last question/post?! @Bro Mo
+sth intersting about age and hiit
Can high-intensity interval training delay the ageing process?

 

[Anna C]

Interesting article on genetic effects

(Edit/Add: Looks like this is about the same study as what you linked just above, @elli )

The Best Exercise for Aging Muscles

Among the younger subjects who went through interval training, the activity levels had changed in 274 genes, compared with 170 genes for those who exercised more moderately and 74 for the weight lifters. Among the older cohort, almost 400 genes were working differently now, compared with 33 for the weight lifters and only 19 for the moderate exercisers.

Many of these affected genes, especially in the cells of the interval trainers, are believed to influence the ability of mitochondria to produce energy for muscle cells; the subjects who did the interval workouts showed increases in the number and health of their mitochondria — an impact that was particularly pronounced among the older cyclists.

 

[mprevost]

Interesting article on genetic effects

(Edit/Add: Looks like this is about the same study as what you linked just above, @elli )

The Best Exercise for Aging Muscles

Among the younger subjects who went through interval training, the activity levels had changed in 274 genes, compared with 170 genes for those who exercised more moderately and 74 for the weight lifters. Among the older cohort, almost 400 genes were working differently now, compared with 33 for the weight lifters and only 19 for the moderate exercisers.

Many of these affected genes, especially in the cells of the interval trainers, are believed to influence the ability of mitochondria to produce energy for muscle cells; the subjects who did the interval workouts showed increases in the number and health of their mitochondria — an impact that was particularly pronounced among the older cyclists.

From the original article:

HIIT was 3 days per week of cycling (4 3 4 min at >90% of peak oxygen consumption [VO2 peak] with 3 min pedaling at no load) and 2 days per week of treadmill walking (45 min at 70% of VO2 peak).

RT consisted of lower and upper body exercises (4 sets of 8–12 repetitions) 2 days each per week.

Their version of HIT falls squarely in zone 4, which is 10K race pace for runners.

I would consider that to be a bit light (intensity) to be called HIT. It is more of a tempo interval. As you can see, lactate would be elevated, but not excessively high like it would be during true HIT intervals.

 

[Anna C]

That makes sense. For me, that would be a HR of ~160 when I'm cycling, which is very hard, but not maxed out or sprinting. I can sustain for 5 minutes or more for repeated intervals, or even longer if I have to, like the 30-60 min shown on the chart (but then really takes a toll, recovery-wise). The legs are burning, the breathing is heavy, the effort is hard -- but it is sustainable. And I can correlate this to the actual Lactate measures I got in my last lab test. So this a "glycolytic" intensity, but the lactate, acidity, and other by-products are being buffered and handled within the body.

What's interesting to me is that the study suggests that this "showed increases in the number and health of their mitochondria ". I sort of had the impression that there were cardiovascular benefits to LT/tempo/zone 4 training, but maybe at a cost to mitochondria. What I'm seeing here is that if I exercise for health, and I believe that number and health of mitochondria is a sign of health or a contributor to health, then this might be a more effective way to accomplish my objectives than just zone 2/LSD.

Is my thinking here logical?

 

[mprevost]

That makes sense. For me, that would be a HR of ~160 when I'm cycling, which is very hard, but not maxed out or sprinting. I can sustain for 5 minutes or more for repeated intervals, or even longer if I have to, like the 30-60 min shown on the chart (but then really takes a toll, recovery-wise). The legs are burning, the breathing is heavy, the effort is hard -- but it is sustainable. And I can correlate this to the actual Lactate measures I got in my last lab test. So this a "glycolytic" intensity, but the lactate, acidity, and other by-products are being buffered and handled within the body.

What's interesting to me is that the study suggests that this "showed increases in the number and health of their mitochondria ". I sort of had the impression that there were cardiovascular benefits to LT/tempo/zone 4 training, but maybe at a cost to mitochondria. What I'm seeing here is that if I exercise for health, and I believe that number and health of mitochondria is a sign of health or a contributor to health, then this might be a more effective way to accomplish my objectives than just zone 2/LSD.

Is my thinking here logical?

HIT has a positive impact on mitochondrial biogenesis. The proposed mechanism is below:

AMP kinase responds to increasing levels of AMP, a breakdown product of ATP. So, when cellular energy levels are low due to lots of ATP breakdown, AMPK signal increases mitocchondrial biogenesis.

However, not all HIT studies have shown an increase in mitochondrial activity or density. Some do not. It could be that at really high intensities with inadequate recovery (and really high lactate), the body upgrades anaerobic enzyme activity instead (i.e., to produce more lactate) to maintain REDOX potential in the cell (see the thread on why we produce lactate). I don't really know at what intensity this might happen and if it really happens at all but it would explain some of the contradictory results. So it is possible (but I don't know for sure) that at low intensity HIT (zone 4 and maybe zone 5), you get mitochondrial biogenesis, but at high intensity (above zone 5, i.e., Tabata), you do not, but get an increase in anaerobic capacity instead. If this is true, it is a sound basis for alactic training.

 

[Anna C]

If this is true, it is a sound basis for alactic training.

Thank you, that is great information!

Trying to make sure I understand the context of the statement I quoted here... Understanding that we don't know for sure, but presenting the possibility that low intensity HIIT (zone 4-ish) might be good for the mitochondria, but above zone 5 not? And if so, would recommend alactic training for mitochondrial health -- which, in this context, refers to the lower intensity HIIT (zone 4-ish) where only a moderate amount of lactate is being produced?

The term "alactic" always throws me off, because lactate is always somewhere in the picture... It's just a matter of relative amounts, and if it's accumulating.

 

[the hansenator]

Interesting article on genetic effects

(Edit/Add: Looks like this is about the same study as what you linked just above, @elli )

The Best Exercise for Aging Muscles

Among the younger subjects who went through interval training, the activity levels had changed in 274 genes, compared with 170 genes for those who exercised more moderately and 74 for the weight lifters. Among the older cohort, almost 400 genes were working differently now, compared with 33 for the weight lifters and only 19 for the moderate exercisers.

Many of these affected genes, especially in the cells of the interval trainers, are believed to influence the ability of mitochondria to produce energy for muscle cells; the subjects who did the interval workouts showed increases in the number and health of their mitochondria — an impact that was particularly pronounced among the older cyclists.

In the absence of a stationary bike, what other types of exercise do you think would give a similar effect that the interval group experienced?

 

[Anna C]

In the absence of a stationary bike, what other types of exercise do you think would give a similar effect that the interval group experienced?

Running, at the targeted HR.

I would think rowing also, but would take some working up to that in technique.

 

[offwidth]

Maybe cross-country skiing; but technique and conditions come into play in a large way

 

[mprevost]

Thank you, that is great information!

Trying to make sure I understand the context of the statement I quoted here... Understanding that we don't know for sure, but presenting the possibility that low intensity HIIT (zone 4-ish) might be good for the mitochondria, but above zone 5 not? And if so, would recommend alactic training for mitochondrial health -- which, in this context, refers to the lower intensity HIIT (zone 4-ish) where only a moderate amount of lactate is being produced?

The term "alactic" always throws me off, because lactate is always somewhere in the picture... It's just a matter of relative amounts, and if it's accumulating.

What I mean by alactic is short duration HIT with plenty of recovery that is done a a really high intensity level bur results in moderate lactate levels because the duration is short and the recovery is long. For example, 25 yard sprints with 2 minutes rest between each sprint.

 

[Anna C]

What I mean by alactic is short duration HIT with plenty of recovery that is done a a really high intensity level bur results in moderate lactate levels because the duration is short and the recovery is long. For example, 25 yard sprints with 2 minutes rest between each sprint.

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