Kreb's cycle and exercise

darrensurrey

No, if you haven't heard of the Kreb's cycle, it's not a new piece of exercise equipment. I've been reading a thread on another site that suggests the likes of HIIT/P90X/Insanity/Tabata/Sprint training are not that useful for fat burning and LISS is actually better. Any thoughts (backed up with proof)? I was under the impression that the other way round was true!

darrensurrey

Anyone?

Azdak

It's way too open-ended a question. There is no simple answer and so the the topic always becomes derailed into ideological posturing.

phjorg1

if fuel source mattered you would want to be as sedentary as possible because the body then uses 100% fat stores to power itself. Thus people who sat around on their *kitten* all day should be the leanest people. right?

obviously you see why this is bogus. fuel source matters jack, because next time you eat, it's filled right back up again. calorie deficit is all that matters. so doing whatever you can to burn more calories will get you further ahead.

edit: that other thread is just rehashing out the fat burning zone BS. 30 years later and people still believe it. sigh

Mr_Knight

Usain Bolt burns somewhere around 10 calories when sprinting 100m faster than any other human alive - you're not going to burn more in your interval training bursts. And there is now sufficient research to show that "after burn" of calories is, at the very most, an insignificant boost, and at worse, is actually a negative number for sprint/interval type training.

Adding intervals to low intensity cardio work has definite fitness benefits (when used in conjunction - it results in worse cardiovascular fitness when used as a replacement), but burning calories is not one of them. If calorie burn is your principle goal, get on a bike or start running an hour a day.

There is no substitute for distance.

primal_cupcakes

Based on the studies I've read, LISS is more appropriate for obese sedentary people coming off the couch, with a little interval training thrown in to induce faster changes. There's my middle-of-the-road, everything-in-moderation answer.

wild_wild_life

I think the term "fat burning" is too vague. Do you mean fat loss? Weight loss? Preferential use of fat for energy?

darrensurrey

For burning fat stored in fat cells over glycogen stored in muscles I guess.

stefjc

Too much depends on the individual but an obese individual would need to be using fat as a fuel store, so longer duration (that is more than a couple of minutes, in energy system terms), medium intensity exercise of any sort will do it.

You want to be into the Krebs cycle as it used tryglycerides as a fuel source and provides lots of ATP so you can continue to work... thus utilising more! And you will utilise more during recovery.

Short sharp exercise won't use triglycerides whilst you are exercising, again you will use more than you would have without any exercise during recovery and repair and growth of muscle fibres will utilise a bit more too.

Sprint Ints will deplete your ATP and glycogen stores, so you will have to reduce intensity and use tryglycerides in order to continue, it may be a little more fuel inefficient to do it that way, so you may get a gain during and after exercise.

But none of that is going to be the same for any 2 people depending on age, gender, fitness levels and a load of genetic predispositions.

Bottom line is you need quantity of exercise of using triglycerides as your main fuel is your goal. And that of necessity means you need to reduce the intensity of the activity you do. How much depends entirely on YOU.....

Oh, you wanted proof... erm any exercise physiology textbook, try McArdle Katch and Katch or any A level PE or Biology textbook.

wild_wild_life

^^ Very well explained, thank you!

My thought is that when people talk about burning fat, what they really want to do is lose fat. And that seems like a dietary issue much more than an exercise issue. If you eat at a caloric deficit you will lose fat and if you eat at a surplus you will store fat, regardless of whether you are doing HIIT, walking, or no exercise at all. So what is exercise's role in fat loss beyond helping to create that calorie deficit?

QuietBloom

^^ Very well explained, thank you!

My thought is that when people talk about burning fat, what they really want to do is lose fat. And that seems like a dietary issue much more than an exercise issue. If you eat at a caloric deficit you will lose fat and if you eat at a surplus you will store fat, regardless of whether you are doing HIIT, walking, or no exercise at all. So what is exercise's role in fat loss beyond helping to create that calorie deficit?

The goal of exercise is to preserve lean body mass while eating at a deficit. Activated muscle is spared muscle. Otherwise, the body says "I don't need that because I am not using it" and burns it as part of the process of creating energy. All bets go through the window, however, when eating a VLCD.

wild_wild_life

^^ Very well explained, thank you!

My thought is that when people talk about burning fat, what they really want to do is lose fat. And that seems like a dietary issue much more than an exercise issue. If you eat at a caloric deficit you will lose fat and if you eat at a surplus you will store fat, regardless of whether you are doing HIIT, walking, or no exercise at all. So what is exercise's role in fat loss beyond helping to create that calorie deficit?

The goal of exercise is to preserve lean body mass while eating at a deficit. Activated muscle is spared muscle. Otherwise, the body says "I don't need that because I am not using it" and burns it as part of the process of creating energy. All bets go through the window, however, when eating a VLCD.

I would think in that case strength training would be the obvious choice. I can see cardio sparing some muscle but I wonder how significant an effect it has. Muscle sparing seems to be a different issue than trying to achieve a "fat burning state" in cardio.

stefjc

Alternatively the goal of exercise is for general health. In which case cardio is essential - it uses muscle too, so that's a win win, isn't it?

Muscle sparing? I am not sure what that means, in context. I know what it means in terms of elite athletes but am not sure what the professed point of it is an exercise arena... especially give the sentence "I don't need that because I am not using it" and burns it as part of the process of creating energy." Muscle is only ever utilised once all other energy sources have been depleted - as at the end of a marathon.

I suspect it may be decent science that has been 'translated' by a lifting guru, but I am not sure as I don't know what you meant by it, QuietBloom.

phjorg1

Alternatively the goal of exercise is for general health. In which case cardio is essential - it uses muscle too, so that's a win win, isn't it?

Muscle sparing? I am not sure what that means, in context. I know what it means in terms of elite athletes but am not sure what the professed point of it is an exercise arena... especially give the sentence "I don't need that because I am not using it" and burns it as part of the process of creating energy." Muscle is only ever utilised once all other energy sources have been depleted - as at the end of a marathon.

I suspect it may be decent science that has been 'translated' by a lifting guru, but I am not sure as I don't know what you meant by it, QuietBloom.

Cardio only used type I muscle. More intense exercise uses type II. Only do cardio, and you lose your type II muscle. So don't use it and you lose it.

phjorg1

^^ Very well explained, thank you!

My thought is that when people talk about burning fat, what they really want to do is lose fat. And that seems like a dietary issue much more than an exercise issue. If you eat at a caloric deficit you will lose fat and if you eat at a surplus you will store fat, regardless of whether you are doing HIIT, walking, or no exercise at all. So what is exercise's role in fat loss beyond helping to create that calorie deficit?

That was very well explained bro science. Calorie deficit is all that matters. Exercise fuel source does not. So you are correct in that exercise is for creating that deficit. Exercises other role is health and lean mass appearance.

stefjc

Accused of bro science - I shall giggle for hours.

wild_wild_life

Accused of bro science - I shall giggle for hours.

Sorry, not allowed. Bros don't giggle, you will have your card revoked.

I don't think it is bro science by any stretch but I guess if you are going to take the next step and say that you need to do X and not Y kind of exercise to "burn fat" and get Z results than it could be entering that realm. But I don't think you implied that.

By muscle sparing I just meant the ability of strength training (I don't know about cardio) to decrease the relative proportion of muscle lost when weight is lost in a calorie deficit. Maybe I didn't use the term correctly.

I think this is all about people looking for that "bio-hack" where if they just do one simple thing (HIIT, fasted cardio, juicing, no carbs after 6, the list goes on), they will get better results. It's human nature. And as long as people are also putting in the hard work required, I don't think there's anything wrong with parsing out the details for a possible workaround. It's just how humans operate and we wouldn't be where we are as a species without it.

stefjc

Ah! I only just got to be a card carrying bro and I ruined it already :-)

By muscle sparing I just meant the ability of strength training (I don't know about cardio) to decrease the relative proportion of muscle lost when weight is lost in a calorie deficit. Maybe I didn't use the term correctly.

Muscle sparing is a medical term that refers to any invasive procedure that actively tries to reduce the amount of separation of muscle fibres. But I have read it a lot here and so suspect it has been used as you describe it, most likely on lifting sites. What you posted is logical but can be greatly exaggerated by those lifting gurus.

I don't read them so I am normally waaaaaaaaaaaaaaaay behind the times and, given the day job, I get confused when a term I use daily is hijacked or given a new meaning in a different context. That's why I asked, thanks for explaining.

Basically, unless you are utterly sedentary, you will lose fat more than you will lose muscle as protein is the least favoured fuel source - as I tried to explain in my bro science post

You are right, I wouldn't suggest any one type of exercise is better than any other. But I am usually irritated by the way cardio gets dismissed by many who like to lift. I like high impact work, but I know I need to do cardio for the sake of my heart and lungs, I am unfit, less healthy than I might be by definition, being overweight will do that to you

And I think most of the arguments on here are caused by that sort of limitation - I want ONE magic thing that will MAKE me lose weight. It's not surprising sometimes. Someone finds a thing that works for them, or get a good understanding of one aspect of a thing, they are bound to share it. Who wouldn't? But sometimes they also lose the wider view....

... and I am in full day job mode. I'll stop!

darrensurrey

Thanks for the replies. Interesting stuff.

NRSPAM

What's LISS?

NRSPAM

Ok, I googled it, and I don't think it would be better. I've heard that interval training is best for burning calories, which eventually will burn more fat. However, you should do whatever you like. The more you love it, the more you'll do it. Sitting doesn't burn as many calories or fat, as any of them.

QuietBloom

Alternatively the goal of exercise is for general health. In which case cardio is essential - it uses muscle too, so that's a win win, isn't it?

Muscle sparing? I am not sure what that means, in context. I know what it means in terms of elite athletes but am not sure what the professed point of it is an exercise arena... especially give the sentence "I don't need that because I am not using it" and burns it as part of the process of creating energy." Muscle is only ever utilised once all other energy sources have been depleted - as at the end of a marathon.

I suspect it may be decent science that has been 'translated' by a lifting guru, but I am not sure as I don't know what you meant by it, QuietBloom.

I'm sorry if my terms were not strictly correct (not sure, but no matter). But actually muscle will be utilized as a fuel source long before all the fat is gone. Examples of that can be seen in just about any weight loss study on pubmed. Fat is a precious resource for the body, and it will protect it to a certain extent. If muscles are not being used, they will atrophy and used for energy. To what extent, I do not know.

QuietBloom

Hmmm. The fast twitch vs. slow twitch muscle makes for interesting thought. *puts on thinking cap*

stefjc

Thanks for explaining, QuietBloom.

The key term there is ALL THE FAT. Protein is always the fuel of last resort, but the last resort comes way before the last of the triglycerides have been used.

Muscle is only ever utilised once all other available triglycerides have been depleted, as opposed to all stored fats, if that clarification helps. As you say the body is protective of certain essential level of fat. It spares glycogen too, as the brain is only fed by glucose/glycogen. So if you are restricting kcals then your stores will be reduced and anabolic processes will have to occur and protein will be utilised, or exercise will be reduced as the individual cannot keep going.

But usually protein is used as a fuel source only when you undertake prolonged exercise and triglycerides and muscle glycogen have been depleted. Then amino acids from muscle breakdown will be oxidised, but will only provide 10 -15% of the energy needed for endurance exercise. So, given what that means in real life terms, it is unlikely to have a significant impact under normal exercise circumstances.

And once you start finding fast and slow twitch muscle fibres interesting your are doomed, doomed I say

Azdak

Thanks for explaining, QuietBloom.

The key term there is ALL THE FAT. Protein is always the fuel of last resort, but the last resort comes way before the last of the triglycerides have been used.

Muscle is only ever utilised once all other available triglycerides have been depleted, as opposed to all stored fats, if that clarification helps. As you say the body is protective of certain essential level of fat. It spares glycogen too, as the brain is only fed by glucose/glycogen. So if you are restricting kcals then your stores will be reduced and anabolic processes will have to occur and protein will be utilised, or exercise will be reduced as the individual cannot keep going.

But usually protein is used as a fuel source only when you undertake prolonged exercise and triglycerides and muscle glycogen have been depleted. Then amino acids from muscle breakdown will be oxidised, but will only provide 10 -15% of the energy needed for endurance exercise. So, given what that means in real life terms, it is unlikely to have a significant impact under normal exercise circumstances.

And once you start finding fast and slow twitch muscle fibres interesting your are doomed, doomed I say

Both the "fat burning" and "muscle eating" ideas fail for the same reason. They assume that the acute, transient response to a workout load somehow results in permanent physical change. That's not how the body works. Physiologically, our bodies are always in a state of flux, always using a mixture of fuel substrates, always experiencing anabolic and catabolic processes, etc. Changes happen when different states are maintained over a long period of time. For example, if someone does utilize amino acids for fuel in a longer, more intense workout, that transient "imbalance" can be easily restored via post-workout feedings (that's the whole point of post-workout feedings).

The same with "fat burning". It has been shown pretty conclusively that, over 24 hours, exercisers burn the same amount and percentage of fat--regardless of the amount/percentage of fat burned during a workout, and even when cellular changes have occurred over time that promote increased fat burning (e.g. increased mitochrondria, increased amount of hormones involved in fat oxidation, etc).

It is a pleasant surprise to see that so many people in this thread have got it right--it's total calories that matter more than anything else. Exercise helps to maintain a calorie deficit, interval training helps to increase fitness level so that one can burn more calories with exercise, exercise (esp resistance exercise) helps to mitigate the loss of lean mass that usually occurs when maintaining a calorie deficit. It really doesn't have to be any more complicated than that.

The one case where 'fat burning" or "HIIT" or even low-carb dieting might play a greater role is in fit individuals with lower body fat percentages. For these people, fat "mobilization" becomes more of a challenge than fat "oxidation" (it's just the opposite with overfat/obese individuals).

CoachDreesTraining

Usain Bolt burns somewhere around 10 calories when sprinting 100m faster than any other human alive - you're not going to burn more in your interval training bursts. And there is now sufficient research to show that "after burn" of calories is, at the very most, an insignificant boost, and at worse, is actually a negative number for sprint/interval type training.

Adding intervals to low intensity cardio work has definite fitness benefits (when used in conjunction - it results in worse cardiovascular fitness when used as a replacement), but burning calories is not one of them. If calorie burn is your principle goal, get on a bike or start running an hour a day.

There is no substitute for distance.

And how many calories does Usain Bolt burn in the following 15-20 minutes when he is out of breathe walking around the track? Calories burned is a product of work, not distance. You can do far more work using intervals than with steady-pace cardio. A lower percentage of these calories will come from fat sources, but all energy must be converted to glucose prior to it being used by the cell, so why does it matter?

phjorg1

Thanks for explaining, QuietBloom.

The key term there is ALL THE FAT. Protein is always the fuel of last resort, but the last resort comes way before the last of the triglycerides have been used.

Muscle is only ever utilised once all other available triglycerides have been depleted, as opposed to all stored fats, if that clarification helps. As you say the body is protective of certain essential level of fat. It spares glycogen too, as the brain is only fed by glucose/glycogen. So if you are restricting kcals then your stores will be reduced and anabolic processes will have to occur and protein will be utilised, or exercise will be reduced as the individual cannot keep going.

But usually protein is used as a fuel source only when you undertake prolonged exercise and triglycerides and muscle glycogen have been depleted. Then amino acids from muscle breakdown will be oxidised, but will only provide 10 -15% of the energy needed for endurance exercise. So, given what that means in real life terms, it is unlikely to have a significant impact under normal exercise circumstances.

And once you start finding fast and slow twitch muscle fibres interesting your are doomed, doomed I say

Both the "fat burning" and "muscle eating" ideas fail for the same reason. They assume that the acute, transient response to a workout load somehow results in permanent physical change. That's not how the body works. Physiologically, our bodies are always in a state of flux, always using a mixture of fuel substrates, always experiencing anabolic and catabolic processes, etc. Changes happen when different states are maintained over a long period of time. For example, if someone does utilize amino acids for fuel in a longer, more intense workout, that transient "imbalance" can be easily restored via post-workout feedings (that's the whole point of post-workout feedings).

The same with "fat burning". It has been shown pretty conclusively that, over 24 hours, exercisers burn the same amount and percentage of fat--regardless of the amount/percentage of fat burned during a workout, and even when cellular changes have occurred over time that promote increased fat burning (e.g. increased mitochrondria, increased amount of hormones involved in fat oxidation, etc).

It is a pleasant surprise to see that so many people in this thread have got it right--it's total calories that matter more than anything else. Exercise helps to maintain a calorie deficit, interval training helps to increase fitness level so that one can burn more calories with exercise, exercise (esp resistance exercise) helps to mitigate the loss of lean mass that usually occurs when maintaining a calorie deficit. It really doesn't have to be any more complicated than that.

The one case where 'fat burning" or "HIIT" or even low-carb dieting might play a greater role is in fit individuals with lower body fat percentages. For these people, fat "mobilization" becomes more of a challenge than fat "oxidation" (it's just the opposite with overfat/obese individuals).

quoted for new page. full agreement.