In order to contract, muscles need energy, or rather a very special fuel, ATP. We can say that muscles are like machines in which chemical energy is converted into kinetic energy. In addition to the fact that muscles use energy and produce it, in the case of long-term running, almost all ATP is produced during training.
Muscles produce ATP during running by converting ATP to ADP. This releases energy in a series of chemical reactions that allow ADP to convert back into ATP. Which provides energy again.
How do we get the energy for running or What makes our muscles move?
ATP stands for adenosine triphosphate, a molecule composed of four elementary molecules, one molecule of adenosine, and three molecules of phosphate. The bond of the phosphate molecule (P) closest to adenosine is different from the others. Those other connections, when broken, give energy. Usually, the outermost bond from adenosine is broken, releasing energy that the muscles can use. The molecule now consists of adenosine and two phosphates (one with an “energy bond”) and is called adenosine diphosphate or ADP.
Muscles can deposit a very small amount of ATP, which is enough for the first few meters of running. In order for the work to continue, the muscles must produce more ATP, which they do with the rest of the previous reactions, in other words, the muscles produce all their fuel from ADP and phosphate (P). This is possible because the complex enzyme systems found in each muscle fiber can use the energy found in other muscles, mostly in the form of carbohydrates and fat from food.
Three systems for getting energy for running
ATP resynthesis occurs in three ways, i.e. using three energy mechanisms: anaerobic alactate, anaerobic lactate, and aerobic. All systems cause a reaction between ADP and phosphate where an ATP molecule is created. The difference between these energy systems lies in the energy source used to bind ADP and phosphate to form ATP.
Anaerobic alactate system
The anaerobic alactate system is typical for short-term activities, lasting up to 20 seconds at most. Energy is created without the presence of oxygen and without the production of lactic acid. When we move from rest, our muscles begin to use the small amounts of ATP found in the muscle fibers, then the ATP is created by creatine phosphate (PCR), which contains one keratin molecule and one phosphate “energy bond”.
When that bond breaks, energy is released that is used to resynthesize ATP from ADP and P. The amount of ATP that can be produced by it (four times greater than the ATP supply) is limited, because there are small amounts of PCR in the muscles. This system is not important for long-term running results.
Anaerobic lactate system
The anaerobic lactate system is also known as the glycolytic system because sugar molecules (glycolysis) are dissolved without the presence of oxygen. Energy from this system is obtained when running at submaximal intensity for a duration of 20 seconds to 3-4 minutes. Sugar molecules, more precisely glucose, are not broken down completely, but only until lactic acid production. Lactic acid molecules are not created in the muscle, but rather negative lactate ions (LA-) and positive hydrogen ions (H+), and the energy needed to produce ATP from ADP and P.
During running, the production of lactic acid in the muscles per second increases as the runner accelerates. Up to a certain speed, the body can eliminate lactic acid from the blood. It is usually absorbed by other muscles or muscle fibers of the same muscle that produced it, the heart, liver or kidneys, so the lactate level in the blood is always close to the basal value.
Lactic acid is produced in the muscles and released into the blood, where its concentration can be measured. Both the blood and muscles are present in two ions, i.e., one molecule and one electrically charged atom. The first is a negatively charged lactate molecule (LA-), and the second is a positively charged hydrogen ion (H+). Hydrogen is actually the one that causes more discomfort. Because it increases the acidity (pH) level in the muscle and can even prevent it from working properly.
When the muscles become acidic
We experience a decrease in muscle efficiency after running at high speed because the level of acidity has increased. When that level increases above a certain value, various changes occur in the muscle. The body will gradually return to its pre-training state. In some cases, this will allow it to tolerate higher levels of acidity. Hydrogen ions not only impair the work of the muscles but also affect the brain because when they are released into the blood, they easily reach the cerebrospinal fluid that surrounds it. Therefore, high production of lactic acid negatively affects mental clarity, movement coordination, and reaction speed. These effects can be partly attributed to ammonia, which the muscles also produce.
The aerobic system is characterized by the fact that energy is obtained with the presence of oxygen. In this system too, energy can be obtained from glucose molecules, but unlike the anaerobic lactate system, here glucose is completely broken down thanks to complex biochemical reactions in the presence of oxygen. These reactions can also take place on the basis of fatty acids. Glucose and fatty acids burn to carbon dioxide and water:
- glucose + oxygen → carbon dioxide + water + energy
- fatty acids + oxygen → carbon dioxide + water + energy
Energy is used to produce ATP from ADP and P in this system. Even a small amount of energy is obtained from the reaction with amino acids, the elementary molecules of proteins. Through breathing, oxygen enters the muscles, specifically the mitochondria, and cellular organelles for aerobic energy production. The result in the race depends on the amount of oxygen supplied to the muscle fibers per minute, and on the amount of oxygen that the muscle fibers can use.