What is energy? What are the energy substances in the body?
Adenosine triphosphate (ATP for short) is the only direct energy source for muscle activity, and it is also the direct energy source for any other cellular activities in the human body (such as the secretion of glandular cells, the excitement of nerve cells, etc.).
ATP is stored in cells, of which muscle cells (also known as muscle fibers) are the most. ATP is composed of a macromolecule called adenosine and three simpler phosphates. The latter two phosphates have high-energy bonds, which store a large amount of chemical energy. Therefore, compounds such as ATP are also called high-energy phosphides.
When a phosphate bond at the end of ATP breaks, energy is released to enable the cell to perform work or complete its physiological function.
During muscle activity, ATP stored in muscle fibers is rapidly decomposed into adenosine diphosphate (ADP) and inorganic phosphorus (Pi) under the catalysis of ATPase, releasing energy, shortening muscle fibers and completing work. However, the reserve of ATP in muscles is relatively small, and it can only maintain the activity of the human body for a few seconds. It must be synthesized while decomposing, so as to continuously meet the needs of muscle activity and make the activity lasting.
In fact, once ATP is decomposed, it will be re-synthesized immediately.
The energy required for re-synthesis depends on the specific conditions of exercise. There are three sources: one is the energy of creatine phosphate decomposition; the other is the energy of glycogen fermentation; the third is the energy of oxidation of sugar and fat (and some proteins).
What are the ways of energy supply in the body?
(1) Decomposition of creatine phosphate (CP for short) is another high-energy phosphide that is stored in muscle fibers and is closely related to ATP. It can release a lot of energy when it is decomposed. When the muscle is contracted and the strength is great, with the rapid decomposition of ATP, CP also rapidly dissociates energy, so that ADP and P can synthesize ATP. Muscles in a quiet state:
High-energy phosphides accumulate in the form of CP, so the content of CP in muscle cells is about 3 to 5 times that of ATP. Nevertheless, its content is also limited. When CP is completely decomposed, it can only maintain vigorous exercise for a few seconds, and there must be other energy to supply ATP to re-synthesize in order to sustain muscle activity.
The important feature of CP energy supply to re-synthesize ATP is its rapid availability. Since CP can quickly dissociate energy without aerobic and does not produce lactic acid, it and ATP together in the energy supply system is called the phosphate system (ATP-CP system)
CP and ATP cannot be directly used as nutritional supplements because their molecules are too large to be absorbed by the body. Creatine can be directly absorbed by the human body, enter muscle cells to synthesize CP, and then be used to synthesize ATP, supply energy for muscle activity, and have a certain good effect on strength training.
(2) When the duration of muscle glycogen digestion exercise is more than 10 seconds and the intensity is high, the energy required by the body has far exceeded what the phosphate system can provide, and the body’s oxygen supply is far from enough to meet the needs. . At this time, ATP re-synthesis energy required for exercise is mainly provided by glycogenolysis.
Glycolysis uses muscle glycogen as the raw material, glycogen is decomposed into glucose, and ATP is generated in the process of continuing to decompose glucose into lactic acid.
When the oxygen supply is sufficient, part of the produced lactic acid is oxidized in the mitochondria for energy generation, and part is synthesized into liver and muscle glycogen.
Excessive accumulation of lactic acid in the body will disrupt the acid-base balance of the internal environment, reduce muscle workability, and cause temporary muscle fatigue. Therefore, relying on glycogen anaerobic glycolysis for energy can only make muscles work for tens of seconds. When anaerobic glycolysis provides energy, oxygen is not needed, but lactic acid is produced, so it is called the lactic acid energy system.
The important significance of the lactic acid energy system is that it can still produce energy in the absence of oxygen to meet the urgent needs of the body.
(3) The aerobic oxidation of sugar and fat. When the supply of oxygen during exercise can meet the oxygen demand, the ATP required for exercise is mainly supplied by the aerobic oxidation of sugar and fat. Aerobic oxidation can provide a lot of energy, which can maintain muscles for a longer working time. For example, the ATP produced by the aerobic oxidation of glucose produced by glycogen is 13 times that of anaerobic glycolysis. This kind of aerobic oxidation energy supply is called an anaerobic oxidation system.
Although the phosphate system and the lactic acid energy system both supply a certain or even most of the energy during exercise, the final synthesis of ATP and CP and the elimination of glycolysis product lactic acid must be achieved through aerobic oxidation. Therefore, the ultimate source of energy for muscle activity is the aerobic oxidation of sugar and fat (and protein in some cases), and sugar and fat come from food.
Protein can also be used as an energy source in the aerobic energy system, but it is usually not used.
It is only when sugar and fat are unavailable that protein is used as an energy source, such as severe hunger for a long time and excessive exercise for a long time.
What is the relationship between the energy supply system and sports?
(1) Although the absolute value of the energy supplied by the phosphoric acid system in the human body is not large and the maintenance time is very short, its main function is the rapid availability of energy.
Short-distance sprinting, jumping, throwing, sprinting, weightlifting, and other sports that need to be completed within a few seconds all rely on the system’s reserve as the main energy source.
(2) The energy of the lactic acid energy system comes from the anaerobic glycolysis of muscle glycogen. The final product of the fermentation is lactic acid. The energy released is received by ADP and then synthesized into ATP. It is the main energy source of the body under hypoxia. Anaerobic training can improve the energy supply capacity of the human lactic acid energy system. When completing the same intense quantitative exercise, the blood lactic acid of the trainer is lower than that of the untrained person.
However, after a short period of strenuous exercise, the blood lactic acid of trainees is 20~30% higher than that of those without training, which is related to the higher glycogen content in the muscles of trainees and increases with the improvement of training level. It is related to the level of glycogen utilization.
The important role of the lactic acid energy system, like the protophosphate system, is to quickly supply energy in the case of temporary hypoxia. For example, when completing a set of exercises in bodybuilding training, it relies on the lactic acid energy system to provide energy.
(3) The aerobic oxidation system refers to the decomposition of sugar or fat into carbon dioxide and water with the participation of oxygen, and at the same time generates a large amount of energy, so that ADP can synthesize ATP again. The aerobic oxidation system is the main energy supply system for long-term endurance activities.
It can be seen that the energy provided by the energy supply system when the human body moves is closely related to special sports. The so-called “anaerobic exercise” refers to exercises in which energy is mainly supplied by anaerobic metabolism (phosphate system and lactic acid energy system) during exercises, such as sprinting, weightlifting, and fitness training.
The so-called “aerobic exercise” refers to exercise that mainly uses the aerobic oxidation system to supply energy during exercise, such as long-distance running, swimming, aerobics, etc. to reduce body fat.
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