Dispelling some exercise myths around glycogen and fat burning
rankinsect
Posts: 2,238 Member
So I've seen several people talk recently about how short duration cardio won't actually help for fat loss, because the muscles will use glycogen as fuel first. This is really TBI - True But Irrelevant - because it only considers the immediate effects and not the long-term effects.
Here's an analogy. Say you get paid in cash every week, and you fill your wallet up to about $100 and deposit whatever's left over in a bank. When your wallet gets low, you go to an ATM and grab some cash to refill your wallet.
Now say you have a $20-per-week habit of buying, I don't know, Legos. Every week you take $20 from your wallet and buy a new Lego set. You argue that this doesn't actually affect your bank account balance at all, because it comes from the money in your wallet. Now, in the moment of purchase, this is true. Your bank balance doesn't immediately drop by $20. However, in the long term, you'll be making some combination of more frequent withdrawls and/or smaller deposits, and over the course of a year, your bank balance is going to be exactly $1,040 less than it would have been without the Lego spending. In the long term it was irrelevant that the money came from your cash reserves and not your savings account.
It's the same sort of effect with glycogen and fat. Yes, if you do 15 minutes of cardio, your body is not likely to metabolize fat in that particular instant to meet that exact energy need. However, as your body eventually regenerates that glycogen, you will have the same amount of net fat loss over time as if it was fully fueling your workout from fat. Most likely, your muscles will replenish that glycogen at your next meal, where it will take calories that would otherwise have been stored as fat, since we all tend to store some new fat after a meal and burn fat in between meals. It might also take glucose from the blood to replenish glycogen and then replenish the glucose from fat. However it does it, over time, this exercise will cause you to lose fat faster, even though not a single fat molecule was directly and immediately oxidized to fuel that workout.
A related myth is the 'fat burning zone' on cardio equipment. Basically, that is the target heart rate that produces the greatest ratio of calories from fat vs. calories from glycogen or other sources. However, again, this is TBI - the actual way to burn the most fat is to burn the most total calories, regardless of where the calories come from, because in the long term the source of the energy is irrelevant.
Here's an analogy. Say you get paid in cash every week, and you fill your wallet up to about $100 and deposit whatever's left over in a bank. When your wallet gets low, you go to an ATM and grab some cash to refill your wallet.
Now say you have a $20-per-week habit of buying, I don't know, Legos. Every week you take $20 from your wallet and buy a new Lego set. You argue that this doesn't actually affect your bank account balance at all, because it comes from the money in your wallet. Now, in the moment of purchase, this is true. Your bank balance doesn't immediately drop by $20. However, in the long term, you'll be making some combination of more frequent withdrawls and/or smaller deposits, and over the course of a year, your bank balance is going to be exactly $1,040 less than it would have been without the Lego spending. In the long term it was irrelevant that the money came from your cash reserves and not your savings account.
It's the same sort of effect with glycogen and fat. Yes, if you do 15 minutes of cardio, your body is not likely to metabolize fat in that particular instant to meet that exact energy need. However, as your body eventually regenerates that glycogen, you will have the same amount of net fat loss over time as if it was fully fueling your workout from fat. Most likely, your muscles will replenish that glycogen at your next meal, where it will take calories that would otherwise have been stored as fat, since we all tend to store some new fat after a meal and burn fat in between meals. It might also take glucose from the blood to replenish glycogen and then replenish the glucose from fat. However it does it, over time, this exercise will cause you to lose fat faster, even though not a single fat molecule was directly and immediately oxidized to fuel that workout.
A related myth is the 'fat burning zone' on cardio equipment. Basically, that is the target heart rate that produces the greatest ratio of calories from fat vs. calories from glycogen or other sources. However, again, this is TBI - the actual way to burn the most fat is to burn the most total calories, regardless of where the calories come from, because in the long term the source of the energy is irrelevant.
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Interesting. I want to be a bit more active. I do NO cardio because I hate it so much, that my thinking was always the 10-15 min. I am actually willing to do will have no impact on my goals....But I guess it could. Still don't know about it.0
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Pretty good anology.0
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Thank you for this. This was a good read.0
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Thanks for this post, very helpful.0
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Good post, as usual, @rankinsect !0
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I agree with the first part of your post, but this second part is more in the 'mostly true' category.rankinsect wrote: »A related myth is the 'fat burning zone' on cardio equipment. Basically, that is the target heart rate that produces the greatest ratio of calories from fat vs. calories from glycogen or other sources. However, again, this is TBI - the actual way to burn the most fat is to burn the most total calories, regardless of where the calories come from, because in the long term the source of the energy is irrelevant.
I think a better analogy is savings in different types of accounts: checking, savings, IRA, stocks and finally your home.
Depending how full your glycogen account is when you start exercise, it will be used first but not to empty. I am not positive, but I think the tendency towards preferential glycogen use depends on where it is stored. Muscle glycogen seems to be readily and preferentially used. Liver glycogen use kicks in somewhere along the line but not to exhaustion before the body starts providing substantial energy from fat burn.
The 'fat burning zone' kicks in after the easily accessible glycogen is used. The reason to not exceed the zone has to do with a body's maximum fat burn rate. If the demand is greater than the fat burn the body will deplete glycogen further and start to recruit protein breakdown.
Your general point however is spot on: exercise more, lose more fat for a constant calorie intake.
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I believe my blood sugar stays higher than it should after meals, but yet I have no excess body fat. So, unlike most cases, ultimately I'm not trying to burn stored body fat. In this case, which would be better: high or low intensity cardio? Or does this not matter?0
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ForecasterJason wrote: »I believe my blood sugar stays higher than it should after meals, but yet I have no excess body fat. So, unlike most cases, ultimately I'm not trying to burn stored body fat. In this case, which would be better: high or low intensity cardio? Or does this not matter?
Do you plan to do cardio right after eating?
What makes you believe that your blood sugar stays higher than it should? Have you been diagnosed by a doctor?
If this is true, then you have some kind of insulin resistance or you are not secreting enough insulin (Type 2 and Type 1 diabetes).
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Glycogen isn't used first - the vast majority of exercise is fuelled from a blend of fat and glycogen (carbohydrate) in differing proportions. During lower intensity exercise fat is the predominant fuel, higher intensity carbohydrate is the predominant source. If I remember correctly the 50/50 point is roughly 70% of max HR but sure someone can correct me.ericGold15 wrote: »
I agree with the first part of your post, but this second part is more in the 'mostly true' category.rankinsect wrote: »A related myth is the 'fat burning zone' on cardio equipment. Basically, that is the target heart rate that produces the greatest ratio of calories from fat vs. calories from glycogen or other sources. However, again, this is TBI - the actual way to burn the most fat is to burn the most total calories, regardless of where the calories come from, because in the long term the source of the energy is irrelevant.
I think a better analogy is savings in different types of accounts: checking, savings, IRA, stocks and finally your home.
Depending how full your glycogen account is when you start exercise, it will be used first but not to empty. I am not positive, but I think the tendency towards preferential glycogen use depends on where it is stored. Muscle glycogen seems to be readily and preferentially used. Liver glycogen use kicks in somewhere along the line but not to exhaustion before the body starts providing substantial energy from fat burn.
The 'fat burning zone' kicks in after the easily accessible glycogen is used. The reason to not exceed the zone has to do with a body's maximum fat burn rate. If the demand is greater than the fat burn the body will deplete glycogen further and start to recruit protein breakdown.
Your general point however is spot on: exercise more, lose more fat for a constant calorie intake.
Research "respiratory exchange ratio" if you want to know more.
Protein plays a very small part in providing exercise energy.
(Good post @rankinsect )0 -
Great post OP, but here my opinion. No matter how long you do cardio it is always going to be better than not doing any cardio. If your goal is to lose weight just keep it simple. (1) exercise 30 mins a day , (2) Try to eat healthy 99% of the time (no one is perfect 1% denotes our flaws), (3) log what you eat, & (4) stay under you daily caloric intake.
That's it, no need to worry about how long my workouts should be? - Just do it, anything is better than nothing.0 -
I usually do some low intensity exercise about 1-3 hours after exercise. My A1C is a little higher than normal and my doctor wanted me to do more exercise.ForecasterJason wrote: »I believe my blood sugar stays higher than it should after meals, but yet I have no excess body fat. So, unlike most cases, ultimately I'm not trying to burn stored body fat. In this case, which would be better: high or low intensity cardio? Or does this not matter?
Do you plan to do cardio right after eating?
What makes you believe that your blood sugar stays higher than it should? Have you been diagnosed by a doctor?
If this is true, then you have some kind of insulin resistance or you are not secreting enough insulin (Type 2 and Type 1 diabetes).
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Great post OP, but here my opinion. No matter how long you do cardio it is always going to be better than not doing any cardio. If your goal is to lose weight just keep it simple. (1) exercise 30 mins a day , (2) Try to eat healthy 99% of the time (no one is perfect 1% denotes our flaws), (3) log what you eat, & (4) stay under you daily caloric intake.
That's it, no need to worry about how long my workouts should be? - Just do it, anything is better than nothing.
If your goal is to lose weight, keeping it simple means eating at a deficit. You don't technically need to exercise or eat "clean".
ETA: And he wasn't saying don't or do cardio. Just addressing about some misinformation people may have in regards to glycogen and fat burning zones.0 -
It's definitely true that it's not all-or-nothing, and that whether the exercise is directly fueled by glycogen or fat is more complex than the overly simplified way I presented it.
That said, the final conclusion still stands - it really doesn't matter where the immediate energy is coming from, because in the long term, any exercise will ultimately reduce fat from what it would otherwise have been, whether by a direct or by an indirect mechanism.0 -
ForecasterJason wrote: »
I usually do some low intensity exercise about 1-3 hours after exercise. My A1C is a little higher than normal and my doctor wanted me to do more exercise.ForecasterJason wrote: »I believe my blood sugar stays higher than it should after meals, but yet I have no excess body fat. So, unlike most cases, ultimately I'm not trying to burn stored body fat. In this case, which would be better: high or low intensity cardio? Or does this not matter?
Do you plan to do cardio right after eating?
What makes you believe that your blood sugar stays higher than it should? Have you been diagnosed by a doctor?
If this is true, then you have some kind of insulin resistance or you are not secreting enough insulin (Type 2 and Type 1 diabetes).
Mine gets higher, too (insulin resistant) but not too high, and it goes down within 2 hours. That's considered normal, because exercise counts as 'stress' and stress raises blood sugars for us. If yours goes too high or stays high for multiple hours, talk to your doctor.
I still haven't figured out what to eat around exercise because of that. I usually eat a small snack beforehand so my liver won't dump insulin if I work harder than intended (mine likes to do that). Afterwards I've been avoiding eating carbs because my BG is already high from sprinting. I don't know if I have to avoid them or not; should I replenish my glycogen stores, etc. Dunno.0 -
I should clarify; I hadn't been doing much cardio prior to having the blood test. After I got my results and talked with my doctor (2-3 months ago), I significantly increased my activity level. My doctor wanted me to retest in a year, although I may see if it's possible for them to retest my A1C sooner than that.cafeaulait7 wrote: »ForecasterJason wrote: »
I usually do some low intensity exercise about 1-3 hours after exercise. My A1C is a little higher than normal and my doctor wanted me to do more exercise.ForecasterJason wrote: »I believe my blood sugar stays higher than it should after meals, but yet I have no excess body fat. So, unlike most cases, ultimately I'm not trying to burn stored body fat. In this case, which would be better: high or low intensity cardio? Or does this not matter?
Do you plan to do cardio right after eating?
What makes you believe that your blood sugar stays higher than it should? Have you been diagnosed by a doctor?
If this is true, then you have some kind of insulin resistance or you are not secreting enough insulin (Type 2 and Type 1 diabetes).
Mine gets higher, too (insulin resistant) but not too high, and it goes down within 2 hours. That's considered normal, because exercise counts as 'stress' and stress raises blood sugars for us. If yours goes too high or stays high for multiple hours, talk to your doctor.
I still haven't figured out what to eat around exercise because of that. I usually eat a small snack beforehand so my liver won't dump insulin if I work harder than intended (mine likes to do that). Afterwards I've been avoiding eating carbs because my BG is already high from sprinting. I don't know if I have to avoid them or not; should I replenish my glycogen stores, etc. Dunno.
I have read that the previous month accounts for 50% of the A1C test. While I was doing some weight training, I spent most of my days being fairly sedentary. I can't say conclusively, but I am suspecting that the issue is post-meal blood sugar levels, considering that my fasting blood sugar is perfectly normal. And the fact that my meals have a decent amount of carbs would support that idea. But then, I think it's also possible that there are other factors (like stress, given that I am a full time college student) or vitamin D insufficiency interfering with my blood sugar control.
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Or not. From 'MedFitness, associated with the U of Michigan:.Glycogen isn't used first - the vast majority of exercise is fuelled from a blend of fat and glycogen (carbohydrate) in differing proportions. During lower intensity exercise fat is the predominant fuel, higher intensity carbohydrate is the predominant source. If I remember correctly the 50/50 point is roughly 70% of max HR but sure someone can correct me.Exercising for longer than 30 minutes shifts the primary macromolecules that are metabolized from glucose to fatty acids. Shifting from glucose and glycogen supplies allows the body to efficiently mobilize and utilize free fatty acids (FFAs) derived from lipids in adipose tissue, which resides mainly under the skin.
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After the first 30 minutes of exercise, the body runs out of its glycogen storage and then turns mainly to what is left of the glucose in the blood and then finally to fat and amino acids derived from muscle protein. Supporting evidence of fatty acid release comes from physiologic research where human gluteal fat cells isolated after 30 minutes of biking showed that cathecholamine induced lipolysis had increased between 35-50% 4. If exercise does not last until 30 minutes then fat burning is never achieved because all of the glycogen is not used u p. So while one may be able to prevent adding fat to the body, one is not metabolizing fat from the adipose tissues during the exercise. In short, exercises aerobically for less than 30 minutes, one is just maintaining the adipose tissue status quo and decreasing muscle mass.
A little Googling found numbers that you mention, based on a 1994 study of endurance athletes studied after an overnight fast.
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ericGold15 wrote: »
Or not. From 'MedFitness, associated with the U of Michigan:.Glycogen isn't used first - the vast majority of exercise is fuelled from a blend of fat and glycogen (carbohydrate) in differing proportions. During lower intensity exercise fat is the predominant fuel, higher intensity carbohydrate is the predominant source. If I remember correctly the 50/50 point is roughly 70% of max HR but sure someone can correct me.Exercising for longer than 30 minutes shifts the primary macromolecules that are metabolized from glucose to fatty acids. Shifting from glucose and glycogen supplies allows the body to efficiently mobilize and utilize free fatty acids (FFAs) derived from lipids in adipose tissue, which resides mainly under the skin.
... ...
After the first 30 minutes of exercise, the body runs out of its glycogen storage and then turns mainly to what is left of the glucose in the blood and then finally to fat and amino acids derived from muscle protein. Supporting evidence of fatty acid release comes from physiologic research where human gluteal fat cells isolated after 30 minutes of biking showed that cathecholamine induced lipolysis had increased between 35-50% 4. If exercise does not last until 30 minutes then fat burning is never achieved because all of the glycogen is not used u p. So while one may be able to prevent adding fat to the body, one is not metabolizing fat from the adipose tissues during the exercise. In short, exercises aerobically for less than 30 minutes, one is just maintaining the adipose tissue status quo and decreasing muscle mass.
A little Googling found numbers that you mention, based on a 1994 study of endurance athletes studied after an overnight fast.
Thanks for the giggles - that article is hilarious!
Running out of glycogen storage after 30 minutes - really?
Think of the burn rate needed to run through approximately 500 grams of carbohydrate in 30 minutes and you will see what nonsense that is.
Think of how far runners can go before they "hit the wall" or how long a cyclist goes before they "bonk". And how awful it feels (crushing and sudden fatigue, mental confusion such as forgetting to put your feet down when you stop pedalling! Yep done that.).
During a 20 minute VO2 max test I went from RER of 0.82 during the gentle start (0.7 is totally fat fuelled) progressively through to RER of 1.0 (totally carb fuelled) after about 15 minutes building to very high intensity and eventually anaerobic at maximal effort / failure.
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Rankinsect you are a treasure here on the boards. Now will you PLEASE address the people who say 'oh hon you need to change up your workout routine because once your body gets use to something you stop burning calories from it.' I could go bald tearing out my hair at that one. LOL0
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Glycogen isn't used first - the vast majority of exercise is fuelled from a blend of fat and glycogen (carbohydrate) in differing proportions. During lower intensity exercise fat is the predominant fuel, higher intensity carbohydrate is the predominant source. If I remember correctly the 50/50 point is roughly 70% of max HR but sure someone can correct me.ericGold15 wrote: »
I agree with the first part of your post, but this second part is more in the 'mostly true' category.rankinsect wrote: »A related myth is the 'fat burning zone' on cardio equipment. Basically, that is the target heart rate that produces the greatest ratio of calories from fat vs. calories from glycogen or other sources. However, again, this is TBI - the actual way to burn the most fat is to burn the most total calories, regardless of where the calories come from, because in the long term the source of the energy is irrelevant.
I think a better analogy is savings in different types of accounts: checking, savings, IRA, stocks and finally your home.
Depending how full your glycogen account is when you start exercise, it will be used first but not to empty. I am not positive, but I think the tendency towards preferential glycogen use depends on where it is stored. Muscle glycogen seems to be readily and preferentially used. Liver glycogen use kicks in somewhere along the line but not to exhaustion before the body starts providing substantial energy from fat burn.
The 'fat burning zone' kicks in after the easily accessible glycogen is used. The reason to not exceed the zone has to do with a body's maximum fat burn rate. If the demand is greater than the fat burn the body will deplete glycogen further and start to recruit protein breakdown.
Your general point however is spot on: exercise more, lose more fat for a constant calorie intake.
Research "respiratory exchange ratio" if you want to know more.
Protein plays a very small part in providing exercise energy.
(Good post @rankinsect )
Bold is worth underlining.
Good post @rankinsect0 -
ericGold15 wrote: »
Or not. From 'MedFitness, associated with the U of Michigan:.Glycogen isn't used first - the vast majority of exercise is fuelled from a blend of fat and glycogen (carbohydrate) in differing proportions. During lower intensity exercise fat is the predominant fuel, higher intensity carbohydrate is the predominant source. If I remember correctly the 50/50 point is roughly 70% of max HR but sure someone can correct me.Exercising for longer than 30 minutes shifts the primary macromolecules that are metabolized from glucose to fatty acids. Shifting from glucose and glycogen supplies allows the body to efficiently mobilize and utilize free fatty acids (FFAs) derived from lipids in adipose tissue, which resides mainly under the skin.
... ...
After the first 30 minutes of exercise, the body runs out of its glycogen storage and then turns mainly to what is left of the glucose in the blood and then finally to fat and amino acids derived from muscle protein. Supporting evidence of fatty acid release comes from physiologic research where human gluteal fat cells isolated after 30 minutes of biking showed that cathecholamine induced lipolysis had increased between 35-50% 4. If exercise does not last until 30 minutes then fat burning is never achieved because all of the glycogen is not used u p. So while one may be able to prevent adding fat to the body, one is not metabolizing fat from the adipose tissues during the exercise. In short, exercises aerobically for less than 30 minutes, one is just maintaining the adipose tissue status quo and decreasing muscle mass.
A little Googling found numbers that you mention, based on a 1994 study of endurance athletes studied after an overnight fast.
Thanks for the giggles - that article is hilarious!
Running out of glycogen storage after 30 minutes - really?
Think of the burn rate needed to run through approximately 500 grams of carbohydrate in 30 minutes and you will see what nonsense that is.
Think of how far runners can go before they "hit the wall" or how long a cyclist goes before they "bonk". And how awful it feels (crushing and sudden fatigue, mental confusion such as forgetting to put your feet down when you stop pedalling! Yep done that.).
During a 20 minute VO2 max test I went from RER of 0.82 during the gentle start (0.7 is totally fat fuelled) progressively through to RER of 1.0 (totally carb fuelled) after about 15 minutes building to very high intensity and eventually anaerobic at maximal effort / failure.
Agreed, it's ridiculous to talk about "running out of glycogen" without mentioning intensity. Light exercise is basically glycogen neutral. High intensity work (RER 1, preferentially CHO fuelled) will reduce global stores to about 20% in one hr in the trained athlete.
What does the bolded above actually mean? Exercising for less than 30 minutes now suddenly decreases muscle mass?ericGold15 wrote: »In short, exercises aerobically for less than 30 minutes, one is just maintaining the adipose tissue status quo and decreasing muscle mass.
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in for the lego.0
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So I always have to laugh that my doctor told me not to exercise when I told her I was trying to lose weight. Not because I medically couldn't, but because many people put on weight when they first start working out, which masks their progress, and they give up before they can see the progress they're making.
I ignored her, but it was a good piece of information to know. It led me too do some more reading, and now I understand a lot more about cortisol, glycogen, and water weight, and how that affects my scale.
I think my doctor is going about it wrong and should be educating and encouraging patients to exercise and diet consistently despite what the scale says. If they expect it, they hopefully wouldn't let it affect them. I don't think people should be encouraged to not workout if they don't have a medical reason that would prevent them.0 -
Following because there are a lot of science nerds up in here.0
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Just a question please- If Protein stores as glycogen and not protein shouldn't the glycogen give a little credit to the proteins calories for its mere existence in a high protein diet?
My 2 cents I love meat, fish, birds,,0 -
Very nice one. How about an insulin one next time? I'm getting tired of the ebil insulin maeks you store all the fat posts.0
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I'm confused so if someone could elaborate...
My understanding is that when we consume carbohydrates (which are the most efficient at providing energy), and to a lesser degree protein, it is converted to glucose and sent through the blood stream where with the help of insulin it passes the cell wall into the cytoplasm of the cell.
With the help of enzymes in this cell it creates 2 molecules of ATP, 2 molecules of NADH, and the rest is converted into pyruvic acid (with the presence of oxygen, it's converted into lactic acid if not whivh must go through an extra step of fermentation to access the energy). This is the process of glycolysis.
Then the pyruvic acid is sent to the mitochondria of the cell where it undergoes the Krebs cycle. The two pyruvic acid molecules are converted into acetyl CoA. The mitochondrion, with the help of free oxygen atoms, oxidizes acetyl CoA into 2 ATP, 6 more NADH, and 2 FADH along with some CO2 which is then respirators out through the lungs.
Then the electrons from the stripped hydrogen atoms pass through the electron transport train resulting in or 32 more molecules of ATP. In other words a total of 36-38 molecules of ATP can be created from a single molecule of glucose.
ATP is the molecule that cells use for energy and with the use of ATPase the phosphate on the end is broken off for use and this is then ADP. It goes through this process of creating ATP and also using/adding phosphate to the ADP molecules over and over.
Edit: this process isn't the most efficient with about 40% of energy being released as body heat. Each molecule of ATP can hold about 7kcals in the phosphate that breaks off when being used for energy.
It's also my understanding that it takes roughly 90 minutes total to burn through glycogen stores before this process of using fat and proteins from muscle tissue begins. Doesn't this also depend on how much carbohydrate you've been consuming, resulting in more free glycogen to be used?
Ultimately, it comes down to total calories consumed throughout a full day and total calories burned. You burn more energy at a higher intensity than you do at a lower intensity (which is relying on fat) over a period of time meaning that even if you are in the fat burning zone for an hour and burn 120 calories total, someone in a higher intensity workout (using glycogen stores) will still burn more overall fat by means of burning more total calories.
Am I totally off base here, or can someone explain.
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The three sources of ATP for the working muscle are the phosphagen system (blue line), non-aerobic glycolysis (red), and the aerobic system (green). The first two is anaerobic (w/o oxygen). When one talk about cardio, we are primarily referring to the aerobic system. Non-aerobic glycolysis is also part of the training regimen to increase the lactate threshold, VO2Max (to genetic limiter and efficiency), and fatigue resistance. For the elite athletes peaking for gold, the phosphagen system are sometime used.- Non-aerobic glycolysis last 45-150 seconds. Type II, or fast-twitch muscles, are the locus for glycolysis using stored muscle glycogen.
- The aerobic system, known as the Kerbs Cycle, provides most of the energy for effort of 3 minutes or longer. Type I, slow-twitching muscle, in conjunction with Type IIa, provides the mechanical work. For fuel, this system relies on fat at lower intensities progressing to carbohydrate as intensity increases.
- The phosphagen system is used during maximal effort which only have enough supply of energy for 10 seconds. Re-phosphorylation of ADP from phosphocreatine stores provides enough for about 25 seconds total. (Structured training utilizing this pathway is HIIT not to be confused by the garbage floating around recently).
As the graph shows, the conversion of fuel to ATP is a continuum tapping into all three pathways depending on intensity. You are using FATs when doing 15 minutes of cardio. How much of it depends on intensity. Total energy expenditure is a different story. The lower the intensity, the lower the burn (and more fat is being used). The trick is finding the biggest bang and that usually around 70-80% of your Lactate Threshold Heart Rate (LTHR). And 15 minutes does not get you anywhere but is a good place to start.0 -
I'm confused so if someone could elaborate...
My understanding is that when we consume carbohydrates (which are the most efficient at providing energy), and to a lesser degree protein, it is converted to glucose and sent through the blood stream where with the help of insulin it passes the cell wall into the cytoplasm of the cell.
in the digestive system carbohydrates break down into glucose and other simple sugars. protein breaks down into amino acids, and fat breaks down into glycerol and fatty acids. glycogen is simply glucose molecules chained together and bound to water molecules. Through gluconeogenesis, glycogen can be made by converting amino acids or fatty acids when simple sugar is not readily avaialable (low carb diet for example).
With the help of enzymes in this cell it creates 2 molecules of ATP, 2 molecules of NADH, and the rest is converted into pyruvic acid (with the presence of oxygen, it's converted into lactic acid if not whivh must go through an extra step of fermentation to access the energy). This is the process of glycolysis.
Close. Glycolysis will create a net of 2 ATP by metabolising glucose as you state. And as a result, pyruvate is left over and H+ ions. If oxygen is available in the mitochondria, then that pyruvate and H+ will be shuttled into the mitochondria where that pyruvate will undergo Krebs Cycle and ETC to produce more ATP (like a little over 30) with the waste products of CO2 and water which you breath out. If oxygen is not available in the mitochondria, then in order to refresh the coenzymes necessary to keep Glycolysis running, the pyruvate is fermented to produce lactate. The H+ ions that are present from normal glycolysis also remain and both accumulate is it is not cleared when oxygen does become available.
Then the pyruvic acid is sent to the mitochondria of the cell where it undergoes the Krebs cycle. The two pyruvic acid molecules are converted into acetyl CoA. The mitochondrion, with the help of free oxygen atoms, oxidizes acetyl CoA into 2 ATP, 6 more NADH, and 2 FADH along with some CO2 which is then respirators out through the lungs.
Then the electrons from the stripped hydrogen atoms pass through the electron transport train resulting in or 32 more molecules of ATP. In other words a total of 36-38 molecules of ATP can be created from a single molecule of glucose.
ATP is the molecule that cells use for energy and with the use of ATPase the phosphate on the end is broken off for use and this is then ADP. It goes through this process of creating ATP and also using/adding phosphate to the ADP molecules over and over.
so now you shifted from how ATP is reformed from metabolizing energy sources through glycolysis and Krebs Cycle/ETC to now how ATP is used to fuel muscle contractions.
Edit: this process isn't the most efficient with about 40% of energy being released as body heat. Each molecule of ATP can hold about 7kcals in the phosphate that breaks off when being used for energy.
It's also my understanding that it takes roughly 90 minutes total to burn through glycogen stores before this process of using fat and proteins from muscle tissue begins. Doesn't this also depend on how much carbohydrate you've been consuming, resulting in more free glycogen to be used?
No. Glycolysis and the use of glucose to form ATP happens simultainously as fatty acids are also used in a modified form of Krebs Cycle/ETC to form ATP as well. There is just a varyring ratios of which gets used more (glucose verses fatty acids). As glycogen gets used up and intensity of the exercise remains releatively low to allow oxygen to be used, the ratio to use fatty acids increase. As intensity increases, then use of glucose has a greater ratio (since less oxygen becomes available to meet the increased demand for energy.
How long it takes to burn through a severe amount of glycogen is not as simple as 90 minutes. Too many factors are involved. I can tell you that for my recent marathon 2 Saturdays ago, I did not hit a severe glycogen depletion. I ran the race in 3 hours 38 minutes. My consumption during the race was basically 2x 32 oz bottles of gatorade or 112 grams of sugar. My pace was on average 8:12 min/mile. My vLT is closer to 7:20 so I was running a lot slower than my threshold pace which allowed me to use a lot more fatty acids then glucose. If I was running closer to my vLT, then my glycogen stores may have been exhausted much faster which is what I did in my marathon run last year where I did bonk at mile 22 (about a little over 3 hours into the race).
By the way, it is very hard to completely deplete all your gycogen stores. Since your brain is a hog for glucose and is very selfish when it comes to that, it will begin shutting down activity in order to preserve that glucose. Thus the bonk. There were experiments done where late in a race when bonking effects were starting to be noticed, the subject has sugar water in their mouth and then immediately spit it out. The effects of bonking started to disappear which signaled the brain (erronously) that more glucose was on the way.
Ultimately, it comes down to total calories consumed throughout a full day and total calories burned. You burn more energy at a higher intensity than you do at a lower intensity (which is relying on fat) over a period of time meaning that even if you are in the fat burning zone for an hour and burn 120 calories total, someone in a higher intensity workout (using glycogen stores) will still burn more overall fat by means of burning more total calories.
Am I totally off base here, or can someone explain.
You get the idea. Just a little off on some of the reasoning. There was some debate on another thread a few weeks ago, but the concensus was that the "fat burning zone" was some made up thing to get you to buy or use treadmills or other similar exercise equipment.
Intensity has an influence on the ratio of glucose to fatty acids but does not strictly define it in one direction or the other. In other words, both glucose and fatty acids are used all the time but in just different ratios. The burning of fatty acids does require oxygen, glucose doesn't need oxygen, but when oxygen is not avilable, the burning of glucose creates more lactate and H+ ions which raises the acidity level in your muscles.
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The three sources of ATP for the working muscle are the phosphagen system (blue line), non-aerobic glycolysis (red), and the aerobic system (green). The first two is anaerobic (w/o oxygen). When one talk about cardio, we are primarily referring to the aerobic system. Non-aerobic glycolysis is also part of the training regimen to increase the lactate threshold, VO2Max (to genetic limiter and efficiency), and fatigue resistance. For the elite athletes peaking for gold, the phosphagen system are sometime used.- Non-aerobic glycolysis last 45-150 seconds. Type II, or fast-twitch muscles, are the locus for glycolysis using stored muscle glycogen.
- The aerobic system, known as the Kerbs Cycle, provides most of the energy for effort of 3 minutes or longer. Type I, slow-twitching muscle, in conjunction with Type IIa, provides the mechanical work. For fuel, this system relies on fat at lower intensities progressing to carbohydrate as intensity increases.
- The phosphagen system is used during maximal effort which only have enough supply of energy for 10 seconds. Re-phosphorylation of ADP from phosphocreatine stores provides enough for about 25 seconds total. (Structured training utilizing this pathway is HIIT not to be confused by the garbage floating around recently).
As the graph shows, the conversion of fuel to ATP is a continuum tapping into all three pathways depending on intensity. You are using FATs when doing 15 minutes of cardio. How much of it depends on intensity. Total energy expenditure is a different story. The lower the intensity, the lower the burn (and more fat is being used). The trick is finding the biggest bang and that usually around 70-80% of your Lactate Threshold Heart Rate (LTHR). And 15 minutes does not get you anywhere but is a good place to start.
Fantastic!!!
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I'm confused so if someone could elaborate...
My understanding is that when we consume carbohydrates (which are the most efficient at providing energy), and to a lesser degree protein, it is converted to glucose and sent through the blood stream where with the help of insulin it passes the cell wall into the cytoplasm of the cell.
in the digestive system carbohydrates break down into glucose and other simple sugars. protein breaks down into amino acids, and fat breaks down into glycerol and fatty acids. glycogen is simply glucose molecules chained together and bound to water molecules. Through gluconeogenesis, glycogen can be made by converting amino acids or fatty acids when simple sugar is not readily avaialable (low carb diet for example).
With the help of enzymes in this cell it creates 2 molecules of ATP, 2 molecules of NADH, and the rest is converted into pyruvic acid (with the presence of oxygen, it's converted into lactic acid if not whivh must go through an extra step of fermentation to access the energy). This is the process of glycolysis.
Close. Glycolysis will create a net of 2 ATP by metabolising glucose as you state. And as a result, pyruvate is left over and H+ ions. If oxygen is available in the mitochondria, then that pyruvate and H+ will be shuttled into the mitochondria where that pyruvate will undergo Krebs Cycle and ETC to produce more ATP (like a little over 30) with the waste products of CO2 and water which you breath out. If oxygen is not available in the mitochondria, then in order to refresh the coenzymes necessary to keep Glycolysis running, the pyruvate is fermented to produce lactate. The H+ ions that are present from normal glycolysis also remain and both accumulate is it is not cleared when oxygen does become available.
Then the pyruvic acid is sent to the mitochondria of the cell where it undergoes the Krebs cycle. The two pyruvic acid molecules are converted into acetyl CoA. The mitochondrion, with the help of free oxygen atoms, oxidizes acetyl CoA into 2 ATP, 6 more NADH, and 2 FADH along with some CO2 which is then respirators out through the lungs.
Then the electrons from the stripped hydrogen atoms pass through the electron transport train resulting in or 32 more molecules of ATP. In other words a total of 36-38 molecules of ATP can be created from a single molecule of glucose.
ATP is the molecule that cells use for energy and with the use of ATPase the phosphate on the end is broken off for use and this is then ADP. It goes through this process of creating ATP and also using/adding phosphate to the ADP molecules over and over.
so now you shifted from how ATP is reformed from metabolizing energy sources through glycolysis and Krebs Cycle/ETC to now how ATP is used to fuel muscle contractions.
Edit: this process isn't the most efficient with about 40% of energy being released as body heat. Each molecule of ATP can hold about 7kcals in the phosphate that breaks off when being used for energy.
It's also my understanding that it takes roughly 90 minutes total to burn through glycogen stores before this process of using fat and proteins from muscle tissue begins. Doesn't this also depend on how much carbohydrate you've been consuming, resulting in more free glycogen to be used?
No. Glycolysis and the use of glucose to form ATP happens simultainously as fatty acids are also used in a modified form of Krebs Cycle/ETC to form ATP as well. There is just a varyring ratios of which gets used more (glucose verses fatty acids). As glycogen gets used up and intensity of the exercise remains releatively low to allow oxygen to be used, the ratio to use fatty acids increase. As intensity increases, then use of glucose has a greater ratio (since less oxygen becomes available to meet the increased demand for energy.
How long it takes to burn through a severe amount of glycogen is not as simple as 90 minutes. Too many factors are involved. I can tell you that for my recent marathon 2 Saturdays ago, I did not hit a severe glycogen depletion. I ran the race in 3 hours 38 minutes. My consumption during the race was basically 2x 32 oz bottles of gatorade or 112 grams of sugar. My pace was on average 8:12 min/mile. My vLT is closer to 7:20 so I was running a lot slower than my threshold pace which allowed me to use a lot more fatty acids then glucose. If I was running closer to my vLT, then my glycogen stores may have been exhausted much faster which is what I did in my marathon run last year where I did bonk at mile 22 (about a little over 3 hours into the race).
By the way, it is very hard to completely deplete all your gycogen stores. Since your brain is a hog for glucose and is very selfish when it comes to that, it will begin shutting down activity in order to preserve that glucose. Thus the bonk. There were experiments done where late in a race when bonking effects were starting to be noticed, the subject has sugar water in their mouth and then immediately spit it out. The effects of bonking started to disappear which signaled the brain (erronously) that more glucose was on the way.
Ultimately, it comes down to total calories consumed throughout a full day and total calories burned. You burn more energy at a higher intensity than you do at a lower intensity (which is relying on fat) over a period of time meaning that even if you are in the fat burning zone for an hour and burn 120 calories total, someone in a higher intensity workout (using glycogen stores) will still burn more overall fat by means of burning more total calories.
Am I totally off base here, or can someone explain.
You get the idea. Just a little off on some of the reasoning. There was some debate on another thread a few weeks ago, but the concensus was that the "fat burning zone" was some made up thing to get you to buy or use treadmills or other similar exercise equipment.
Intensity has an influence on the ratio of glucose to fatty acids but does not strictly define it in one direction or the other. In other words, both glucose and fatty acids are used all the time but in just different ratios. The burning of fatty acids does require oxygen, glucose doesn't need oxygen, but when oxygen is not avilable, the burning of glucose creates more lactate and H+ ions which raises the acidity level in your muscles.
Thank you! This whole process was fuzzy to me and I was just kind of winging it with the "well, I get the concept I think so it's okay". Good to know and I think I finally understand!!
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