Energetic processes in the muscle
The figure shows the prevailing energy sources during load execution
ATF
The universal source of energy in a living organism is the ATP molecule, which is formed in the citrate cycle of Crabs. Under The action of the ATPase enzyme, the ATP molecule is hydrolyzed, detaching the phosphate group in the form of orthophosphoric acid (H3PO4), and turns into ADP, thus releasing energy.
ATP + H2O = ADP+ H3PO4 + energy
The head of the myosin bridge in contact with actin has ATPase activity and, accordingly, the ability to split ATP and get the energy necessary for movement.
The amount of ATP contained in the muscle is sufficient to perform movements for 2-5 first seconds
Creatine phosphate
The supply of ATP molecules in the muscle is limited, so the energy consumption during the work of the muscle requires constant replenishment, this is due to creatine phosphate. Creatine phosphate has the ability to detach the phosphate group and convert to creatine, attaching the phosphate group to ADP, which is converted to ATP.
ADP + creatine phosphate = ATP + creatine.
This reaction is called the Loman reaction. This is why creatine is very important in bodybuilding.
It should be noted that creatine is only effective when performing anaerobic (strength) exercises, since creatine phosphate is sufficient for about 2 minutes of intensive work, then other energy sources are connected. Accordingly, in athletics, taking creatine as a Supplement to increase athletic performance is not advisable.
The reserves of creatine phosphate in the fiber are not large, so it is used as an energy source only at the initial stage of muscle work, until the activation of other more powerful sources – anaerobic and then aerobic glycolysis. At the end of the work of the muscle, the Loman reaction goes in the opposite direction, and the reserves of creatine phosphate are restored within a few minutes.
Energy metabolism of skeletal muscles
Fig. 3. Metabolic pathways of ATP synthesis used during muscle contraction and relaxation. While anaerobic cleavage of CF and glycolysis occur in the cytosol, oxidative phosphorylation occurs in the mitochondria.
Alactate mechanisms
CF provides a reserve of phosphate energy for ATP resynthesis from ADP at the onset of contractile activity (Fig. 3):
KF + ADP creatine Kinase K + ATP (1)
At rest, muscle fibers increase the concentration of CF up to five times more than ATP. At the beginning of the reduction, when the concentration of ATP begins to fall, and ADP increases due to the acceleration of ATP decomposition, mass activity contributes to the formation of ATP from CF.
Although the formation of ATP from CF is rapid, requiring a single enzymatic reaction (1), the amount of ATP that can be obtained from this process is limited by the initial concentration of CF. Muscle fibers also contain myokinase, which catalyzes the formation of one ATP molecule and one AMP molecule from two ADP molecules. ATP and CF combined can provide maximum strength for 8-10 seconds. Thus, the energy received from the phosphagenic system is used for short bursts of maximum muscle activity required in light and heavy athletics (100 m race, shot put, or weight lifting).
Glycolysis
Although glycolytic pathway metabolism produces only a small amount of ATP from each digested glucose unit, it can provide rapid synthesis of a large amount of ATP if sufficient enzymes and substrate are present. This process can also occur in the absence of oxygen:
Glucose anaerobic rapid glycolysis 2 ATP + 2 lactate (2)
Glucose for glycolysis comes either from the blood or from glycogen stores. When the starting material is glycogen, three ATP molecules are formed from one unit of glucose consumed as a result of phosphorolytic glycogenolysis. As muscle activity becomes more intense, more and more ATP is required for anaerobic cleavage of muscle glycogen, and lactic acid production increases accordingly. Anaerobic glycolysis can provide energy for 1.3“ 1.6 min of maximum muscle activity.
The formation of lactic acid lowers the pH level in the muscle fibers. This prevents the action of enzymes and causes pain if the removal of lactic acid is too slow compared to its formation.
Oxidative phosphorylation
At moderate levels of physical activity, such as running at 5,000 m or a marathon,most of the ATP used for muscle contraction is formed by oxidative phosphorylation. Oxidative phosphorylation can release much more energy from glucose compared to anaerobic glycolysis alone:
Glucose +02 - > 38 ATP + C02+ H20. (3)
Fats are catabolized only by oxidative mechanisms, and a lot of energy is released. Amino acids can also be metabolized in a similar way. The three metabolic pathways of ATP formation for muscle contraction and relaxation are shown in figure 3.
During the first 5~10 minutes of moderate physical activity, the main "fuel" consumed is the muscle's own glycogen. Over the next 30 minutes, blood-borne substances become dominant; blood glucose and fatty acids contribute approximately the same amount to muscle oxygen consumption. After this period, fatty acids become increasingly important. It is important to emphasize the interaction between anaerobic and aerobic mechanisms in the formation of ATP during exercise. The contribution of anaerobic ATP formation is greater at short-term high-intensity loads, while at longer-term low-intensity loads, aerobic metabolism predominates.
Recovery and oxygen debt
After physical activity is over, oxygen uptake still remains above normal (table). Recently, the term "excess oxygen consumption after exercise"has also been used to refer to oxygen debt. At first, its level is very high, while the body restores the reserves of CF and ATP, returning the stored oxygen to the tissues, and then for another hour the consumption is at a lower level, while the lactic acid is removed. Therefore, the early and last phases of oxygen debt are called alactate and lactate oxygen debt, respectively. An increase in body temperature also indicates a higher metabolic rate and increased oxygen consumption.
The longer and more intense the physical activity, the longer it takes to recover. For example, it often takes several days to recover from complete muscle glycogen depletion, rather than the seconds, minutes, or hours required to restore CF and ATP stores and remove lactic acid. High-intensity physical activity probably leads to microtraumas of muscle fibers, and their recovery takes some time.
Components of oxygen debt. After prolonged, heavy physical activity, breathing remains above normal to meet the increased oxygen demand
Component
Explanation
1
Recovery of oxygen reserves in tissues(about 1 l)
2
Recovery of creatine phosphate and other energy-rich phosphates (about 1-1. 5 l)
3
Removal of lactic acid by gluconeogenesis and other ways (up to 12 l)
4
Stimulation of metabolism due to increased levels of epinephrine (about 1 l)
5
Additional oxygen consumption in the respiratory muscles and heart (about 0.5 l)
6
Overall increased metabolism due to higher body temperature*
* - increasing the temperature by 10 °C can double the rate of metabolism, if the cells can cope with such changes in temperature
