When it comes to the body’s energy supply and long-distance running, it’s highly relevant to know that the depots of carbohydrate (glycogen) are limited, whereas fat is an infinite energy source. How to economize with Glycogen in a marathon is therefore crucial because hitting the wall means you run out of glycogen and switch over to fat combustion. This article is about glycogen in endurance training.
Glycogen and Work Intensity
When the work intensity is high, but not higher than you can cope with the aerobic processes, the body will get the most ATP (The body’s fuel) per. Oxygen amount if it chooses to combust glycogen. This is favorable since the amount of oxygen is the limiting factor in long-distance running. Therefore, it is important to utilize Oxygen that coming to the muscles in the best way and that will be by combusting glycogen.
Glycogen becomes hereby the body’s “high octane fuel”. At lower intensities, the Oxygen supply is usually abundant relative to demand.
The body will choose to save on the glycogen as it only has in limited quantities and instead combusts fat. It costs more oxygen per. ATP re-formed, but in return, we save on the glycogen. The most important to understand is the reason why we want to train our ability to absorb oxygen in the blood and thus in the muscles is, we will use up our depots of glycogen too quickly if we only combust anaerobic (without oxygen).
The muscles combust carbohydrates up to 10 times faster if they combust anaerobic than if they combust aerobically. This has a great significance on a marathon distance, which lasts between 2 – 6 hours.
Glycogen and Fat
Carbohydrates are stored as glycogen in muscle cells and the liver. About 20 to 40 % are located in the liver, while the rest are ready for use in the muscles. In a normal person are glycogen depots on 200 to 300 grams. Through training, you can increase the size of the glycogen depots in the muscle’s and top-trained athletes can have more than 800 grams.
Larger glycogen depots mean that you can run for a longer period at a given Oxygen uptake. Fat depots are mainly stored around the intestines, internal organs in the body and under the skin. Men’s depots tend to gather around the belt, while fat on females is around hips, buttocks and thighs. One kg of pure fat contains 8000-9000 calories.
The body’s choice of glycogen vs fat
The combustion in the body’s muscles depends on several factors and some of them may be affected by training and diet. In particular, two conditions are relevant:
- The greater intensity of work the greater is the glycogen needs.
- The better aerobic fitness the greater fat combustion at a given work intensity.
Let’s assume that, you run with an intensity of 70 % of VO2 max. (Maximum Oxygen uptake) If you are top-trained, you will be able to run for 2 – 3 hours before the glycogen stores are empty. When the glycogen depots become nearly empty, the combustion in the muscles switching over to fat combustion. When it comes to long-distance races as a marathon, this phenomenon is called” hitting the wall”.
The effect is that you have to slow down the pace because the workability deteriorates significantly when switching from “high octane” to “low octane” fuel. Since marathon training often takes more than 2 hours with the long runs, it’s extremely important to have filled glycogen depots, so the entire training session accomplishes with optimal intensity, because it gives the best results.
With regular marathon training, you train your body to “burn fat”. The body’s general metabolic chemistry changes too, mainly through the production of fat-degrading enzymes, which increases a lot. There is also an increase in the growth hormone somatotropin, which increases the fat combustion while it inhibits the combustion of glycogen.
Daily, you can optimize glycogen anabolism by paying attention to three factors:
- The time of the day, you intake carbohydrates
- The right type of carbohydrates
- A sufficient quantity of carbohydrates
Just after the completion of training, it is important as soon as possible to consume some simple carbohydrates such as bananas or raisins. Quickly, because the transport of carbohydrates into the muscles is increased in a short time after the training is completed.
Between ½ – 1 hour after training, you can take a larger meal with a high content of both simple and complex carbohydrates. Protein contributes only with a minimal amount of energy about 4 % under normal conditions.
Glycogen and run
The main reason that you as a long-distance runner should compose and intake a diet with high content of carbohydrates, is that you can store more than twice as much glycogen in the muscle tissues as by intake of a normal diet.
In addition, you can increase the training duration by nearly twice as much compared to the training duration by intake a normal diet. Glycogen depots are so important for endurance and running performances.
Maybe you have heard about the communal Marathon meal the day before the Marathon race. These meals are mainly Pasta-based since pasta consists of more than 70% carbohydrates. The reason is we want to fill up our glycogen depots in preparation for the big marathon race tomorrow.
In practice, You can’t fill your muscles with glycogen from just one meal the day before. So, you should start the carb-loading two or three days before your race. But it’s still a good tradition with “the day before the meal”.
Stored carbohydrate (glycogen) is the only nutrient that without oxygen can form ATP. ATP is the body’s fuel, formed from nutrients. When the depots are depleted, exhaustion can occur, since fat combustion without glucose in presence, gives accumulation of waste products primarily as lactate that gives a burning sensation in the muscles and at some point, you will “hit the wall” – where the glycogen depots are depleted.
During intensive work like in interval training, where glycogen stores are nearly emptied, the amino acid alanine includes as an energy supplier.
Alanine is a muscle protein that releases from the working muscles. The amino acid cleaves in the liver and a glucose molecule is formed, which can be used as fuel for the working muscles. However, a breakdown of muscle tissue will occur.
So, like a long-distance runner, you want a high consumption of glycogen. Therefore, it is important to eat a diet with a high content of carbohydrates, which also means a relatively poor content of fat and protein. For a long-distance runner, the energy distribution could look like this:
Carbohydrates 55 – 70 %
Proteins 10 – 15 %
Fat 20 – 30 %
For an actual Meal plan and the importance of Vitamins, minerals & traces for long-distance runners, I can recommend my blog post here to find out more about this subject.
If we want the best results in our Marathon training- and races we have to optimize our glycogen depots during intake of the right nutrition distribution. Daily, we also have to pay attention to the three factors in optimizing glycogen anabolism. It will be an individual decision from your current running level whether you want to start a nutrition plan.
I hope you like this post and if you have any questions about this topic about The body’s choice of glycogen vs fat or want to leave your own Personal review, please leave a comment below.