How long does it take to deplete glycogen?

Are you trying to lose weight, or understand better for training?

I tried a hard bike ride one morning without eating. I bonked in about 30 minutes.

During marathons, typical bonk is around 2 hours or 20 miles.

Higher intensities, will be quicker but don't know about 5K races -- it will use a lot.

I propose to just figure this out in training. That was one of the great learning effects when I dabbled for 2 years in trail ultra running.

Books don't provide an answer for this (it's just science). The body is remarkably different. Just think "miler vs letsrunner" and you can picture the differences in digestion.

Your info came from a gel company. It takes closer to 1:45 to completely deplete a full tank.

jimmyjonny wrote:

That sounds false. According to that, you can burn through almost all of your glycogen in only a 5k race. Which means you burn almost 2000 calories when you race a 5k? Bull

'Calories' is not a useful term in biology. 500g of glucose will create different amounts of ATP depending on which energy pathway it does down. If working "anaerobically" (quotation marks because that's a simplistic and ambiguous term) then ATP yield is 15-16 times less per unit of glucose than if working "aerobically".

Also a 2x4 has a lot of calories in it but that doesn't mean they are accessible.

Can you explain a little more please? Are you saying if you are working really hard like 90-95% MHR, pushing anaerobic like in intervals, you are burning through your say 500g of glycogen at a much quicker rate than steady state?

I just want to hear more. if Calories are not useful in biology, then what's their purpose? Energy burned can be defined in a caloric measurement..

Most distance runners carry enough muscle and liver glycogen for about 22mi of running at marathon pace or 30mi at an easy pace.

How quickly you burn through your glycogen depends on how fast you are running.

The caloric cost of running in terms of calories per mile is, to a first-order approximation, flat. That is, running one mile in 5min burns no more or less calories than running one mile in 10 minutes. The difference, of course, is that the five minute mile takes half as much time.

However, where these calories come from is not the same. Again, to a first order approximation, your percentage of VO2 max is equal to the proportion of your calories that come from carbohydrates. The rest is fat. So when you run 5k pace (~98-100% VO2 max) you get ~95-100% of your calories from carbohydrates. When you jog very slowly, more than half your calories can come from fat.

Whatever source you read that info you posted from is wrong. It's not a time-based thing, it's an intensity-based thing. If you were burning 100% glyocgen for fuel, you'd run out of energy after 13-19mi. But nobody can run at 100% VO2 max for that far so it doesn't matter. In a marathon, at ~80-85% VO2 max, the typical runner will "hit the wall" around 21-23mi without any external carbohydrate ingestion. At easy to moderate run pace (55-70% VO2 max) you can last much longer.

Coincidentally this is why long easy runs aren't as useful as you think in marathon training. If you do a 22mi easy run and think you "bonked" at 20mi, in reality you probably just got muscularly fatigued. You didn't run far enough to deplete glycogen stores. There is some fatiguing effect once your stores start to dwindle (below a "tank level" of ~30%) probably due to centrally mediated anticipatory fatigue but you won't really crash until you run out.

These models also assume you have a distance runner build with ~20% of your body mass in your legs. If you are a big hulking upper-body lifter with tiny legs, or if you have a big beer belly, you will run out of glycogen faster. If you are a Kenyan with tiny calves, a plucked-chicken-like upper body, and gigantic thighs, you'll last longer.

Limey UK wrote:

jimmyjonny wrote:

That sounds false. According to that, you can burn through almost all of your glycogen in only a 5k race. Which means you burn almost 2000 calories when you race a 5k? Bull

'Calories' is not a useful term in biology. 500g of glucose will create different amounts of ATP depending on which energy pathway it does down. If working "anaerobically" (quotation marks because that's a simplistic and ambiguous term) then ATP yield is 15-16 times less per unit of glucose than if working "aerobically".

But the lactate eventually gets burned for energy "aerobically" later. It doesn't just disappear. Net energetic yield is the same.

A nutritionist who spoke to my running club told us you should refuel ~40-45 minutes if you are doing gels. I've been following her advice since and have not had those bonkish moments I used to get when I waited longer.

She doesn't use gels, she has stuff she uses in her water so she can keep her levels even throughout the race. I don't like carrying water for a race and I'm not fast enough to get a spot at the elite table so that is a non-starter for me.

dsfasdfadsfs wrote:

Limey UK wrote:

'Calories' is not a useful term in biology. 500g of glucose will create different amounts of ATP depending on which energy pathway it does down. If working "anaerobically" (quotation marks because that's a simplistic and ambiguous term) then ATP yield is 15-16 times less per unit of glucose than if working "aerobically".

But the lactate eventually gets burned for energy "aerobically" later. It doesn't just disappear. Net energetic yield is the same.

Correct, mostly. Re-converting lactate during an interval training session sends most of the lactate back to the muscles and some to the liver for revonversion to glycogen this uses up a small proportion of total energy contained in the lactate molecules.

Right. And the fastest pace that you can handle without lactate accumulation above ~3mmol is the lactate threshold, intensity that you could keep up about 90min or little longer without extra energy intake, before running out of glycogen. So 2.05 marathoners are running the race very close to the lactate threshold.

jimmyjonny wrote:

Can you explain a little more please? Are you saying if you are working really hard like 90-95% MHR, pushing anaerobic like in intervals, you are burning through your say 500g of glycogen at a much quicker rate than steady state?

I just want to hear more. if Calories are not useful in biology, then what's their purpose? Energy burned can be defined in a caloric measurement..

There are a few important things to note:

1- The 500g thing is different for each person based on training status and diet. Someone who trains a lot and has a high carb diet will have more glycogen available in their body than someone who doesn't train and eats low carb.

2-Calories burnt per mile are relatively equal buuuuuut the amount of energy you get from each calorie is different based on the energy systems being used and in what proportion they're being used (all 3 are always being used but in differing amounts). Aerobic metabolism nets 36-38 ATP while anaerobic nets 2 ATP.

To add to the 2 vs 36-38 ATP thing...

This is due to metabolic efficiency. Anaerobic metabolism is not efficient while aerobic metabolism is. You can burn the same number of calories but not receive an equal return for your calorie due to intensity.

Northern Star - great contribution as always

A couple of questions:

A high school athlete running in a XC race at 98% of VO2 max could deplete glycogen in in 15-18 minutes and consequently stagger late in the race?

Also, how would you restore glycogen for a race a week later?

Studier of Nutrition wrote:

To add to the 2 vs 36-38 ATP thing...

This is due to metabolic efficiency. Anaerobic metabolism is not efficient while aerobic metabolism is. You can burn the same number of calories but not receive an equal return for your calorie due to intensity.

So anaerobic is less efficient and uses more energy than aerobic but burns the same calories during exercise but will burn more calories after exercise due to an oxygen debt aka EPOC?

Not quite. The lactate threshold is only sustainable for roughly 45min in a race situation. It's not a true steady-state; it's more of a "metastable" state in that lactate DOES accumulate eventually, once you get past 20-25min of constant work at that pace. So if you are in 45:00 15k shape and you start running 3min/km, your blood lactate level is stable for about 20-25min, starts to creep up slightly, and after about 30min starts to shoot up quite a lot.

One study (http://link.springer.com/article/10.1007/s00421-002-0783-1) defined VLT as the fastest speed that results in an increase in blood lactate of no more than 1.0 mM between the 10th and 30th minute of exercise. Traditionally the LT is defined as 4.0 mM (millimoles of lactate per liter of blood) but there is individual variability in where this boundary actually lies.

Can't speak about 2:05 marathoners since I'm not aware of any research on them. As Canova says, these elites are "different animals" - they may well have different bioenergetic wiring that allows them to run faster or for longer at intensities that, even in relative terms, are unsustainable for a regular runner like you or me.

Again even if you did somehow run at 100% of VO2 max continually, you have enough glycogen to last 13-19 miles. A 5k XC race won't ever deplete your glycogen in any realistic situation. People stagger at the end of 5k races because they are deep in oxygen debt and their muscles cannot fire properly while swamped in a soup of biochemical waste products (or their brain won't let the muscles fire; pick your theory).

The two ATP you get from "anaerobic metabolism" are the first two of the 36/38 ATP you get from "aerobic metabolism." Glycolysis (2 ATP yield) is the first step of oxidative phosphorylation (36/38 ATP). It's not "A or B" it's "A then B" assuming you have oxygen available. If not, it's "A then B, and also more A. Also more B, but not now--I don't have any oxygen available."

When you sprint a 200, where do you think all that lactate goes? It doesn't just disappear; you didn't burn it. It's eventually burned "aerobically" too. Just not during exercise...usually. But now we're getting into the lactate shuttle / MCT protein rabbit hole.

But in terms of net calories overall, it's not different. Otherwise HIIT would be pointless for weight loss, and it's clearly not.

Northern Star wrote:

Not quite. The lactate threshold is only sustainable for roughly 45min in a race situation. It's not a true steady-state; it's more of a "metastable" state in that lactate DOES accumulate eventually, once you get past 20-25min of constant work at that pace.

You are probably talking about MLSS, I´m talking about the lactate threshold; you don´t accumulate much more than ~3mmol lactate, it´s the true steady state intensity. So you can stay at this intensity until you are running out of glycogen.

Marius Bakken about the lactate threshold, where he defines his LT to be the intensity where he could stay ~95minutes:

"Let me explain ; my personal experience is that the most accurate way of running "threshold training" is staying at a lactate level of around 3.0 mmol/l during the sessions (vs. about 4.0 that some literature say - but that 4.0 figure is largely based on athletes that does not have long enough endurance background. The longer you train your endurance, the lower this figure will be !) You can vary from around 2.2 to 3.3, which seems ideal.

In terms of heart rate this is approximately 80-87 %, though expect a variation from morning to afternoon of about 5 beats lower in the morning.

In terms of pace, my personal experience is that this is between your marathon pace and your half marathon pace, depending on where you are in your training cycle. In my case, the threshold before my 13.06 5k (measured 5 days before) was 2.53-54 pr km at 3.0 mmol/l, at 87-89 % of maximum heart rate (you can push this threshold heart rate higher when you are in peak shape) and I could easily stay there for the intervals. This pace would be between my marathon and half marathon pace (Circa CP 95` for Marius)"

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