Metabolism
Metabolic processes form the basis of life for every single cell and therefore for the entire organism. Metabolism serves to build and maintain the body and is responsible for providing energy. Accordingly, we differentiate between the building material metabolism and the operating metabolism.
Metabolism converts foreign substances into the body's own substances. For example, the body converts animal proteins from food intake into the body's own amino acids. Metabolism serves to build and maintain cells, tissues and organs and ensures adaptation to increased stress.
The term "energy metabolism" is also used for the operating metabolism. Energy metabolism is used to generate energy in the form of adenosine tri-phosphate (ATP) for various cellular functions. Energy supply therefore includes processes that are involved in the formation of ATP. ATP is the universal "means of payment" for all cellular services. Around 30 kg of ATP is broken down in the body every day. When an ATP is split, adenosine di-phosphate (ADP), a Pi and energy are released. The energy is utilised by the cells and ADP + Pi are converted back into energy-rich ATP. This occurs via various biochemical processes in which fats and glucose are broken down to CO2 (carbon dioxide) and H2O (water). The more intensively a muscle fibre works, the faster ATP is broken down and the faster it has to be replaced: The rate of ATP formation must keep pace with the rate of ATP consumption. The muscle fibres have different ways of producing ATP. Each body cell is responsible for the production of ATP and it is possible to improve these production processes through training.
Processes of the energy supply
ATP reserve: Every muscle fibre has a stored supply of ATP. This must never be used up completely, otherwise the cell will die. To prevent this from happening, the biochemical processes for ATP production are activated immediately when ATP is consumed.
The processes are divided into aerobic and anaerobic and lactacidic or alactacidic. Aerobic means that oxygen is required for the process and anaerobic means that no oxygen is required. Lactacid means that lactic acid (lactate) is produced during the biochemical process and alactacid means that no lactate is produced. The problem with lactacidic energy production processes is that the muscle can become "over-acidified" and thus fatigue quickly.
Anaerobic-alactacid energy supply
This process is extremely fast and requires creatine phosphate (KrP), a substance that is stored in every muscle fibre. When ATP is broken down, the KrP quickly releases its phosphate and ATP is immediately produced again, which can be used again. No lactate is produced and the process does not require oxygen. During moderate exercise, the KrP stores are continuously replenished. Once the stores are completely depleted, it takes 30-60 seconds of recovery before the stores are refilled (compare breaks between strength exercises). However, the KrP store cannot generate enough ATP to supply the cells with energy during prolonged exercise. Further processes are therefore necessary.
Anaerobic-lactacid energy supply
This process, also known as glycolysis, does not require oxygen but has the disadvantage that lactate is produced. During glycolysis, glucose is broken down directly into pyruvate, which can quickly generate ATP. This process takes place all the time, but is particularly pronounced during high and short workouts. If, for example, you start strength training directly with a high load, you commit an oxygen debt, which can end in over-acidification of the muscles.
Aerobic phosphorylation
There are two processes in this area, in which either glucose or fat is utilised. In the aerobic part of glucose metabolism, the end product of anaerobic glycolysis, i.e. pyruvate, is used. It is first converted into acetic acid and then broken down in the cell, using oxygen, to CO2 and water. Glycolysis is therefore not only responsible for rapid ATP production, but also prepares the starting product used for aerobic glucose metabolism.
The second aerobic process is fat burning. Fat is converted into activated acetic acid, which is then broken down by the cell into CO2 and water, just as in aerobic glucose metabolism. This process takes a long time and is therefore slower than the breakdown of glucose. Furthermore, more oxygen is required to burn fat. However, the reserves are almost inexhaustible. This process can cover the energy requirement in a resting state and runs continuously. If the load is increased, the other energy supply processes come into play more. Fat burning is also intensified under stress and consumption is highest at 55-65% of VO2max. The fat burning process can be improved through training.
Metabolism and exercise intensity
In principle, all processes are always used simultaneously to provide energy. However, depending on the load, one or other energy supply process takes on the main burden of energy supply.
Anaerobic threshold
A distinction is made between two thresholds in energy metabolism. In zone 1, almost 100% of the energy is provided aerobically. Activities can therefore be carried out for hours. As soon as the intensity increases, the body begins to activate anaerobic energy supply processes and the aerobic threshold is exceeded. From this point onwards, lactate is formed. If the intensity of the activity is very high or is increased further during exercise, the anaerobic threshold is reached. This threshold describes the point at which lactate production exceeds the rate of degradation. Another term for the anaerobic threshold is MAXLASS = Maximum Lactate Steady State, i.e. the state where lactate production and breakdown are in balance. If this threshold is exceeded, "over-acidification" occurs (pH value in the blood drops) and thus a drop in performance, which often leads to the termination of the activity.
The anaerobic threshold is very important for training planning and control. It is also a good indicator in performance diagnostics.
VO2max
Maximum oxygen uptake or "oxidative capacity" is the abbreviated name for this value, known as VO2max, which is often used in performance diagnostics. To determine the V02max, the oxygen uptake is measured over a certain period of time at maximum exertion using the spirometry method. Physiological parameters that influence the value of VO2max are:
diffusion capacity of the alveoli, lung volume and performance of the respiratory muscles
blood transport capacity (amount of haemoglobin)
pumping capacity of the heart
density of the capillary network (diffusion capacity of the muscles)
muscle capacity for oxygen uptake
The VO2max thus provides a very broad overview of physical performance. However, only the area of oxygen processing is measured, which is why this indicator is mainly used in sports where endurance has a major influence.