The body gets energy by decomposing the foods and fluids we intake. The condition for the body to decompose the dietary constituents is that there is enough oxygen present. Every cell in the body needs oxygen to live – to get energy. The oxygen supply has an upper limit since the body only can absorb a certain amount per minute, which depends on physical fitness – the training level. We get to a practical Glycogen definition about why Glycogen energy depots are the best running fuel:
Muscle Glycogen
Glucose is the main source of fuel for our cells. The stored form of glucose is made up of many connected glucose molecules, which are called glycogen. When the body doesn’t need glucose for energy, it will be stored in the liver and muscles.
When you need energy, glycogen is broken down to release glucose into the bloodstream and used as fuel for the cells. How it works in practice is illustrated above.
When the body doesn’t need to use glucose for energy, it stores it in the liver and muscles. This stored form of glucose is made up of many connected glucose molecules and is called glycogen. Muscle glycogen serves mainly as a source of what we call metabolic fuel for your muscles. Your muscles need lots of energy to function – for you to move.
Oxygen Consumption Increases with Work Intensity
By increasing workloads such as running, increases the muscle’s need for energy and thus the need for oxygen. The increased need for oxygen is the reason why you get winded and breathe faster when you run. VO2 Max (Maximum oxygen uptake) is the maximum aerobic capacity to perform sustained aerobic efforts.
In long-distance running – with distances from about 2 km and up – you run with an intensity that is lower than the limit for the maximum oxygen uptake. This kind of running consists of aerobic work. We call that Endurance training or LSD run.
By aerobic work means work or an activity where the energy release in the muscles takes place by the presence of oxygen. This kind of decomposing means the combustion of carbohydrates (glycogen) and fat. If you, on the other hand, run so fast that you cannot release enough energy only by using oxygen as in a short intensive sprint.
You have to receive a large part of the energy from decomposing processes without the presence of oxygen. This type of decomposing also takes place with Glycogen (carbohydrate) as an energy source but without oxygen, we call it anaerobic work.
The general by-product of anaerobic decomposing is lactic acid (lactate). The amount of lactic acid in the blood increases with intensity and if the intensity continues to increase, there may not be enough oxygen to cover the total energy needed. Gradually accumulates lactate in the muscles and the amount will begin to limit the muscle’s ability to pull together and get them to stiffen and thus limit the speed. It can burn and hurt, while it may be difficult to coordinate the running steps properly.
Glycogen & Energy Conversion – The Function Of Glycogen
Let’s take a step further with the body’s energy supply. During work, is the chemical energy transformed into mechanical work in the muscles. Muscles can transform energy in different ways, but there is only one process, that can provide energy directly to muscle contraction. This process is the cleavage of adenosine triphosphate ATP to ADP, which releases energy for muscle work.
ATP exists only in very small quantities in muscles. Therefore, ATP has to be re-formed the other way from ADP to ATP again with the same speed as it decomposes to keep up a constant work. All other energy-producing processes are responsible to provide energy so the ATP can reform. When ATP is reformed, it uses as an “energy supplier” again to the muscle work.
The muscle’s supply with energy to rebuild ATP from nutrients partly with oxygen availability (aerobic processes), and partly without oxygen available (anaerobic processes), the basic can expresses as:
ATP → ADP + Energy
Unfortunately, is the case that there is only ATP storage for about 2 seconds of work, and if nothing happens, the muscle will collapse quickly. At relatively low intensity, when we run at an easy to moderate pace with a good oxygen supply, the muscles choose to break down fat to obtain energy.
Combustion of fat is like this:
Fat + Oxygen + ADP → Carbon dioxide + ATP + Water
Waste products are carbon dioxide and water, which we get rid of through exhalation and sweat.
Energy conversion of carbohydrates (Glycogen) can divide into 2 phases:
1) Glycogen + ADP → Lactate + ATP
2) Lactate + Oxygen + ADP → Carbon dioxide + ATP + Water
How to ensure the energy supply
When there is not sufficient oxygen supply to the muscles to produce enough energy by aerobic processes, the muscle ensures the energy to rebuild ATP via an increased anaerobic decomposing of glycogen. As seen in the first phase 1), there is no oxygen-consuming (anaerobic combustion).
The lactate arising in this phase at low/moderate intensity will include in the second phase as fuel 2). It means the result of the combustion of carbohydrates by low/moderate intensity is:
Glycogen + Oxygen + ADP → Carbon dioxide + ATP + Water
When the intensity increases so much that the system no longer can keep up with converting lactate to energy, there will be an accumulation of lactate in the muscle. In the beginning, the muscle feels burning, later as paralyzed and it will no longer be possible to continue with the same intensity.
By measuring the content of lactate in the blood, we can get an insight into the intensity of work.
When we start our running, it will take a few minutes before our aerobic systems activate, and therefore there will be anaerobic combustion with an accumulation of lactate. However, the lactate will quickly disappear when the aerobic processes start up.
Enzymes Support Glycogen Conversion
In muscle fibers are some substances known as enzymes, which play a vital role in the muscle’s ability to work. Enzymes in general are proteins that control the speed of chemical reactions in living organisms.
The enzyme includes in the processes but consumes not. Through specific enzymes, is the individual muscle fiber able to optimize and regulate the energy conversion.
Some of these enzymes are involved in the final decomposing of fat and glycogen. The more aerobic trained a muscle fiber is, the greater the quantity and activity of these specific enzymes in the muscle fiber. It means a larger energy conversion by aerobic processes because the energy production maximizes.
Thus, you will have a more effective run. Conversely, decreases the content of these enzymes by inactivity – if you do not run for a period. However, it takes more time to increase the number of enzymes than it takes to lose them.
Fat and Glycogen
We have seen that these are the critical components of the energy Supply. They are the crucial factors in Marathon training when we go for the best results. The Body uses Glycogen and fat as energy but the choice of either glycogen or fat depends mainly on the presence of Oxygen.
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