Kreb's cycle and exercise

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  • QuietBloom
    QuietBloom Posts: 5,413 Member
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    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
    QuietBloom Posts: 5,413 Member
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    Hmmm. The fast twitch vs. slow twitch muscle makes for interesting thought. *puts on thinking cap*
  • stefjc
    stefjc Posts: 484 Member
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    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
    Azdak Posts: 8,281 Member
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    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
    CoachDreesTraining Posts: 223 Member
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    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
    phjorg1 Posts: 642 Member
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    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.

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