low glycogen stores vs low fitness levels

Azdak wrote: »

jjpptt2 wrote: »

Azdak wrote: »

goatg wrote: »

Yes. There's a difference between having the fuel (glycogen) and athletic conditioning. Eg my first 100 mile ride (previous longest was 77). I still remember pedaling home at 12 mph (flat), with gu in my back pockets, feeling like death.

And around the neighborhood for 4 miles just to say I did it. Heh.

Just an addition: part of “athletic conditioning” is “having the fuel”. The ability to store, break down, process, deliver, and conserve glycogen are all part of the “training effect”.

Hmmm... Can you go a little further with this, or should I just Google "training effect"? I feel like the quality of info from that search would be iffy, at best.

I'm happy to do my own research, just need to be pointed in the right direction. Thanks.

I’m not sure you’d find this on a website. This is more textbook stuff. If you looked at the better-known exercise physiology text books they would have more detailed listings of specific changes—although I’m not sure it would be all that instructive.

Suffice to say that if you observe any increase in physical/athletic performance, that performance and “fitness” improvement is the result of dozens of physiological adaptations to a training stimulus. From macro changes like increased stroke volume and plasma volume to microscopic changes in gene expression and cell membrane permeability. In response to any chronic stressor (e.g. training load), the body will always respond in every conceivable way to reestablish homeostasis.

I’m happy to try to answer any specific questions, but it’s kind of a broad topic to write about in totality.

Stoshew71 wrote: »

I didn't really read the whole thread. Just the OP's post.

I agree. It is very possible that people get "tired" into some X number of miles not just because they lost "energy" in the form of blood sugar, or glycogen, or xyz. If you can pinch an inch, you have more than enough energy to run 3 marathons. The matter becomes being able to access that energy.

It's very most likely that the person in question has plenty of blood sugar or glycogen. But, they are either running at a pace much faster than they should (beyond their lactate threshold) or their aerobic capacity just isn't built for the level of distance they are attempting (or as the OP stated, "a person just isn't trained to exercise that far, that long, that hard".

People that the OP is referring to most likely have not understood the concept that in order for energy to be used, not only do you need a substrate like sugar, but you also need oxygen in the muscle mitochondria. People who are not trained properly, have not developed the mechanism to get the oxygen in their breath to their muscles so that sugar (glucose specifically) or fatty acid can become oxidized so that ATP can be produced in order to allow muscle contractions to continue to occur at the same intensity so the person can continue running whatever distance they are trying to run. Eating a gel at mile 8 is not going to substitute a good aerobic mechanism. That's because the person who isn't trained well isn't lacking sugar, but oxygen.

As the OP correctly observed, "most people probably just need to log more miles and more hours, and be a bit more patient". But I will add, those added miles need to be ran at an aerobic level of effort not an anaerobic level. In normal speaking terms, you run at a pace that you can very easily carry a conversation, not at a pace that makes you huff and puff. If you can't say more than, "this hurts" as you're running because your breathing too hard, then you really need to slow down. Running at an anaerobic level basically means that you are running with too much intensity that you can no longer use oxygen to maintain most of the ATP production to sustain your running. You are now requiring your body to burn glucose inefficiently that creates a fermented byproduct called lactate along with loose ionized hydrogen atoms that causes your muscles and blood to be acidified. When that happens, a signal is sent to your brain which in turn your brain sends another signal back to your muscles to make them stop running. That is the real reason people don't have enough "energy" to run 8 miles at that unbelievable pace.

Stoshew71 wrote: »

janejellyroll wrote: »

Azdak wrote: »

goatg wrote: »

Yes. There's a difference between having the fuel (glycogen) and athletic conditioning. Eg my first 100 mile ride (previous longest was 77). I still remember pedaling home at 12 mph (flat), with gu in my back pockets, feeling like death.

And around the neighborhood for 4 miles just to say I did it. Heh.

Just an addition: part of “athletic conditioning” is “having the fuel”. The ability to store, break down, process, deliver, and conserve glycogen are all part of the “training effect”.

This is an excellent point. I don't have experience with other endurance sports, but a big portion of what your body is doing during long runs is getting your body adjusted to breaking down and delivering the glycogen you need during longer activities. I have to assume it's the same during extended bike rides and other activities of that sort.

(At least according to what I've read about long runs).

Actually, the purpose of the long run is to get your body adjusted to breaking down fatty acids that you need during longer activities.

I posted yesterday and mentioned substrates. Substrates could be glucose or fatty acids being oxidized to produce ATP. Getting a little deeper here now.

Your body (specifically your muscles) prefers to use glucose as the substrate. Your brain however craves glucose and can't really use fatty acids. In long term stress due to low carb diets, the body will start producing a glucose like substance out of your stored fat called ketones to fuel your brain and body. But that is a different topic altogether.

Your body under normal conditions will prefer to use glucose as a substrate because the process to break down glucose into pyruvate then into ATP is much simpler than the process to break down fatty acids into ATP. But you can store much more potential energy in fat than you can from sugar, and therefore your body prefers to store fat long term than sugar.

Sugar is first stored by chaining glucose molecules together and bounded by water molecules and is called glycogen. One gram of glycogen can yield about 3 calories of energy. One gram of fat can yield about 9 calories of energy. Your body will convert excess glucose and can store them as triglycerides (fat) for longer term use. But again, your body would much prefer to break down glycogen into glucose than to break down triglycerides into fatty acids.

The problem, because glycogen is stored by binding sugar with water, there is a limit as to how much your body will store carbs (sugar) in the form of glycogen. It stores a bit in your muscles cells and a whole bunch more in your liver. The most common stat that gets quoted is that your body has the capacity to store about as much glycogen to allow you to run 20 miles. This is a very rough stat, but very much quoted and probably the easiest to understand. Because of this, people say, the marathon is half done at 20 miles and the second half is the last 6.2 miles. Basically, if you want to run anything past 20 miles, you have to get your body to use fat as a substrate to produce ATP.

There are some rules. Your body can use glucose as a substrate to produce ATP without oxygen. It's an inefficient way but your body will go "anaerobic" to burn glucose to produce a small amount of ATP but yield a lot of lactate and Hydrogen ions as byproducts (which I mentioned yesterday will acidify your muscles and blood which causes fatigue). But in order to use a fatty acid as a substrate to produce ATP, your body must be able to oxidize it in the muscle mitochondria. In other words, it requires oxygen. The faster you run, the more you are forcing your body to use carbs over fat. So one of the rules to training your body to use fat is to pace yourself. You have to do your long run in an "aerobic" state and stay away from going "anaerobic". This means you try to do your long run in a conversational state. Talk in complete sentences with a running partner or sing a song out loud as you are running by yourself. If you can't, then you know to slow your pace down. If you get out of breath, then you are going anaerobic and forcing your body to continue to rely more on carbs.

The second rule is that in order to use a substrate, it must be broken down into it's simplest form. Glycogen must first be broken down into glucose (process called glycogenolysis) because certain enzymes are released to help enable that. Your body will also release other hormones to trigger this to happen. For example, your brain will tell the body to release epinephrine as the primary messenger signal to initiate glycogenolysis. Then there are secondary messengers and the process gets very complicated from there. There's a whole completely different process to do the same thing but with fat as opposed to sugar. With all these "chemicals" being released into your body, sometimes it takes a while for your body to chemically shift from sugar burning to fat burning. And your body has to learn to produce enough of these chemicals to support what it is your doing. If you never ran 15 miles before, there's a lot of things your body is just not used to doing. One of them is to adequately produce enough hormones and enzymes so they can be released. To know when to release one thing and not the other. The more you run long distances at an aerobic pace, you are training your body to now convert more to fat burning to fuel the running muscles (keep a bit of glucose burning for the brain and preserved to prevent bonking). For those that advocate low carb high fat diets and be fueled on ketones, it's the same concept. You have to train your body to do that. And you have to eat a certain way to do that as well.

Back to carb burners. The longer and further you run, the more of a shift from glucose burning to fat burning (as long as the pace is correct). The further you run at an anaerobic level, the closer you get to bonking (not good). The more you practice this process, the quicker your body will adjust from primary carb burning to primary fat burning. Another way to practice this in your long run is to run in an already carb depleted state. In other words fasted running (as opposed to fed running). You can also google "train low race high" as a training technique that explains this in more detail. The concept is basically, you can run a long time until your body sufficiently depletes enough glycogen in order to shift the carb burning to fat burning. But you can achieve a similar effect if you don't eat anything for a while (fasted running) - like run as soon as you get up and don't eat anything - your body is already in a glycogen depleted state and will make the shift to fat burning within a shorter period of time. The further you run in this depleted state, the more you stress your body to be better prepared the next time you do this type of workout.