Anaerobic pathways for ATP resynthesis are additional pathways. There are two such pathways: the creatine phosphate pathway and the lactate pathway.
The creatine phosphate pathway is associated with the substance creatine phosphate. Creatine phosphate consists of the substance creatine, which binds to the phosphate group via a high-energy bond. Creatine phosphate in muscle cells is contained at rest at 15 – 20 mmol/kg.
Creatine phosphate has a large energy reserve and high affinity for ADP. Therefore, it easily interacts with ADP molecules that appear in muscle cells during physical work as a result of the ATP hydrolysis reaction. During this reaction, a phosphoric acid residue with a reserve of energy is transferred from creatine phosphate to an ADP molecule with the formation of creatine and ATP.
Creatine phosphate + ADP → creatine + ATP.
This reaction is catalyzed by the enzyme creatine kinase. This ATP resynthesis pathway is sometimes called creatikinase.
The creatine kinase reaction is reversible, but is biased toward ATP production. Therefore, it begins to take place as soon as the first ADP molecules appear in the muscles.
Creatine phosphate is a fragile substance. The formation of creatine from it occurs without the participation of enzymes. Creatine not used by the body is excreted from the body in urine. Creatine phosphate synthesis occurs during rest from excess ATP. During moderate muscular work, creatine phosphate reserves can be partially restored. The stores of ATP and creatine phosphate in muscles are also called phosphagens.
The maximum power of this pathway is 900-1100 cal/min-kg, which is three times higher than the corresponding indicator of the aerobic pathway.
Deployment time is only 1 – 2 seconds.
Operating time from maximum speed only 8 - 10 seconds.
The main advantage of the creatine phosphate pathway for ATP formation is
· short deployment time,
· high power.
This reaction is the main source of energy for exercise maximum power: running on short distances, throwing jumps, lifting the barbell. This reaction can be triggered repeatedly during execution physical exercise, which makes it possible to quickly increase the power of the work performed.
Biochemical assessment of the state of this ATP resynthesis pathway is usually carried out by two indicators: creatine ratio and alactic debt.
Creatine ratio is the excretion of creatine per day. This indicator characterizes the reserves of creatine phosphate in the body.
Alactate oxygen debt– this is an increase in oxygen consumption in the next 4–5 minutes, after performing a short-term exercise of maximum power. This excess oxygen is required to provide high speed tissue respiration immediately after the end of the load to create an increased concentration of ATP in muscle cells. In highly qualified athletes, the value of alactic debt after performing maximum power loads is 8–10 liters.
The glycolytic pathway of ATP resynthesis, like creatine phosphate, is an anaerobic pathway. The source of energy necessary for ATP resynthesis in this case is muscle glycogen. During the anaerobic breakdown of glycogen, the terminal glucose residues in the form of glucose-1-phosphate are alternately cleaved from its molecule under the action of the enzyme phosphorylase. Next, the glucose-1-phosphate molecules, after a series of sequential reactions, are converted into lactic acid. This process is called glycolysis. As a result of glycolysis, intermediate products are formed containing phosphate groups connected by high-energy bonds. This bond is easily transferred to ADP to form ATP. At rest, glycolysis reactions proceed slowly, but with muscular work, its speed can increase 2000 times, and already in the pre-start state.
The maximum power is 750 – 850 cal/min-kg, which is two times higher than with tissue respiration. This high power is explained by the presence of a large supply of glycogen in the cells and the presence of a mechanism for activating key enzymes.
Deployment time is 20-30 seconds.
Operating time at maximum power is 2-3 minutes.
The glycolytic method of ATP formation has a number of advantages over the aerobic way:
· it reaches maximum power faster,
· has a higher maximum power,
· does not require the participation of mitochondria and oxygen.
However, this path also has its drawbacks:
- the process is not economical,
- the accumulation of lactic acid in the muscles significantly disrupts their normal functioning and contributes to muscle fatigue.
To assess glycolysis, two biochemical methods are used - measuring the concentration of lactate in the blood, measuring the blood pH and determining the alkaline reserve of the blood.
The lactate content in urine is also determined. This provides information about the total contribution of glycolysis to providing energy for the exercises performed during training.
Another important indicator is lactate oxygen debt. Lactate oxygen debt is an increased oxygen consumption in the next 1 - 1.5 hours after the end of muscular work. This excess oxygen is necessary to eliminate lactic acid formed during muscle work. Well-trained athletes have an oxygen debt of 20–22 liters. The size of the lactic debt is used to judge the capabilities of a given athlete under submaximal power loads.
Creatine phosphoric acid (creatine phosphate, phosphocreatine) - 2-[methyl-(N"-phosphonocarboimidoyl)amino]acetic acid. Colorless crystals, soluble in water, easily hydrolyzed with cleavage of phosphamide N-P connections in acidic environment, stable in alkaline environment. Creatine phosphate is a product of reversible metabolic N-phosphorylation of creatine, which, like , is a high-energy compound.
Restoring phosphate levels
If an athlete begins a set without adequately restoring phosphate levels, he will not be able to maintain energy production throughout that or subsequent sets. Thus, during the maximum strength phase of training, athletes should have a rest period of three to five minutes before performing subsequent sets using the same muscle group, unless the athlete is working with a large reserve. To maximize recovery when performing exercises at very high intensity and with little reserve, athletes should use a vertical training technique, i.e. move on to a new exercise after completing a set of the previous exercise. In other words, the athlete performs one set of each exercise before returning to the very first exercise and performing the second set. As a result of using this algorithm, a sufficient period of time remains for the restoration of phosphate levels in the muscles.
Duration of recovery of ATP-CP levels
Reduction of phosphagens (ATP and KrP)
Phosphagens, especially ATP, are restored very quickly (Fig. 25). Already within 30 s after stopping work, up to 70% of the consumed phosphagens are restored, and their complete replenishment ends in a few minutes, almost exclusively due to the energy of aerobic metabolism, i.e., due to the oxygen consumed in the fast phase of O2 debt. Indeed, if immediately after work you tourniquet the working limb and thus deprive the muscles of oxygen delivered through the blood, then restoration of KrF will not occur.
How The greater the consumption of phosphagens during operation, the more O2 is required to restore them (to restore 1 mole of ATP, 3.45 liters of O2 are required). The magnitude of the fast (alactate) fraction of O2 debt is directly related to the degree of decrease in phosphagens in the muscles at the end of work. Therefore, this value indicates the amount of phosphagens consumed during the work process.
U In untrained men, the maximum value of the fast fraction of O2 debt reaches 2-3 liters. Particularly large values of this indicator were recorded among representatives of speed-strength sports (up to 7 liters among highly qualified athletes). In these sports, the content of phosphagens and the rate of their consumption in the muscles directly determine the maximum and maintained (remote) power of the exercise.
Glycogen restoration. According to the initial ideas of R. Margaria et al. (1933), glycogen consumed during work is resynthesized from lactic acid within 1-2 hours after work. The oxygen consumed during this recovery period determines the second, slow, or lactate, fraction of O2-Debt. However, it has now been established that the restoration of glycogen in muscles can last up to 2-3 days
Speed glycogen restoration and the amount of its restored reserves in the muscles and liver depend on two main factors: the degree of glycogen consumption during work and the nature of the diet during the recovery period. After a very significant (more than 3/4 of the initial content), up to complete, depletion of glycogen in the working muscles, its restoration in the first hours with normal nutrition is very slow, and it takes up to 2 days to reach the pre-working level. With a diet high in carbohydrates (more than 70% of daily calories), this process accelerates - already in the first 10 hours more than half of the glycogen is restored in the working muscles, by the end of the day it is completely restored, and in the liver the glycogen content is significantly higher than usual. Subsequently, the amount of glycogen in the working muscles and liver continues to increase and 2-3 days after the “depleting” load it can exceed the pre-working load by 1.5-3 times - the phenomenon of supercompensation.
At daily intensive and long-term training sessions The glycogen content in working muscles and liver decreases significantly from day to day, since with a normal diet, even a daily break between workouts is not enough to completely restore glycogen. Increasing the carbohydrate content in an athlete’s diet can ensure complete restoration of the body’s carbohydrate resources by the next training session.
Elimination lactic acid. During the recovery period, lactic acid is eliminated from working muscles, blood and tissue fluid, and the faster, the less lactic acid is formed during work. The after-work regime also plays an important role. So, after maximum exercise, it takes 60-90 minutes to completely eliminate accumulated lactic acid under conditions of complete rest - sitting or lying down (passive recovery). However, if after such a load light work is performed (active recovery), then the elimination of lactic acid occurs much faster. For untrained people, the optimal intensity of the “recovery” load is approximately 30-45% of the VO2max (for example, jogging), a. in well-trained athletes - 50-60% of MOC, for a total duration of approximately 20 minutes.
Exists four main ways to eliminate lactic acid:
- 1) oxidation to CO2 and SHO (this eliminates approximately 70% of all accumulated lactic acid);
- 2) conversion to glycogen (in muscles and liver) and glucose (in liver) about 20%;
- 3) conversion to proteins (less than 10%); 4) removal with urine and sweat (1-2%). With active reduction, the proportion of lactic acid eliminated aerobically increases. Although the oxidation of lactic acid can occur in a variety of organs and tissues (skeletal muscles, heart muscle, liver, kidneys, etc.), the largest part of it is oxidized in skeletal muscles (especially their slow fibers). This makes it clear why light work (which involves mostly slow-twitch muscle fibers) helps clear lactate more quickly after heavy exercise.
Significant part of the slow (lactate) fraction of O2 debt is associated with the elimination of lactic acid. The more intense the load, the larger this fraction. In untrained people it reaches a maximum of 5-10 liters, in athletes, especially among representatives of speed-strength sports, 15-20 liters. Its duration is about an hour. The magnitude and duration of the lactate fraction of the O2 debt decrease with active reduction.
ATP- the energetic basis of human movements. ATP is broken down during movement and synthesized during rest. In bodybuilding, 3 modes of ATP reproduction are used: aerobic mechanism, glycogen and lactic acid, phosphagenic mechanism. In addition to the reproduction of ATP by humans, there are ways to obtain ATP from the outside, for example, a method of obtaining ATP intramuscularly.
ATP in muscles
Adenosine triphosphate (ATP, also known as adenine) is a molecule that serves energy basis all biological processes of the human body. ATP in muscles used to carry out movements. The muscle fiber contracts under the influence of the breakdown of adenine, after which a certain amount of energy is released, which is used for muscle contraction. In the human body, adenosine triphosphate is obtained from inosine (brand name: , inosine, ribonosine, etc.).
If ATP is broken down during muscle contraction, then during moments of rest, on the contrary, it is synthesized. By and large, ATP in muscles is nothing more than a biological battery that stores energy when it is not needed. On the other hand, releasing it if the need for energy arises.
The role of ATP in energy metabolism is very large. Without ATP, the human body would not be able to carry out the life process. A person needs energy supply for metabolism, transportation of various molecules, etc. Muscle contraction is not possible without the energy obtained from ATP.
ATP structure
Three components are included in ATP structure:
1.Triphosphate
If we consider the ATP molecule, then in its center there is a ribose molecule, its end is the beginning for adenine, which is clearly shown in the figure above. The triphosphate is on the opposite side of the ribose. ATP fills a protein-containing fiber called myosin. This is a fibrillar protein, which is one of the main components of contractile muscle fibers. Myosin is responsible for the formation of all muscle cells. One of the main properties of myosin is the ability to break down ATP.
Reproduction of ATP
The amount of ATP is not unlimited. On average, after a few seconds of movement, its quantity is exhausted. This means that it needs to be replenished. Humans have special mechanisms that reproduce ATP structures:
- Aerobic respiration
- Glycogen and lactic acid
- Phosphagen system
These energy exchange mechanisms come into operation at a strictly defined time. In bodybuilding, where high repetitions are most often practiced, all 3 systems are used. But in speed-strength sports, the second and third predominate.
Bodybuilding involves extremely intense workloads. Since the most powerful source of resynthesis ATF in bodybuilding- this is creatine phosphate (the third mechanism of ATP synthesis), then increasing its amount will lead to the fact that a person will be able to train intensively for a longer time.
ATP energy is used during skeletal muscle activity for 3 processes:
■ operation of a K + -Na + pump, ensuring a constant concentration gradient of K + and Na + ions on both sides of the membrane;
■ the process of sliding of actin and myosin filaments, leading to shortening of myofibrils;
■ the work of the calcium pump necessary to relax the fiber.
When muscles work, chemical energy is converted into mechanical energy, i.e. muscle is a chemical engine, not a thermal one. The processes of muscle contraction and relaxation require ATP energy. The cleavage of ATP with the detachment of one phosphate molecule and the formation of adenosine diphosphate (ADP) is accompanied by the release of 10 kcal of energy per 1 mole: ATP = ADP + P + En. However, ATP reserves in muscles are small (about 5 mmol/l). There are only enough of them for 1 - 2 s work. The amount of ATP in muscles cannot change, because in the absence of ATP, contracture develops in the muscles (the calcium pump does not work and the muscles are unable to relax), and in the absence of ATP, elasticity is lost.
To continue working constant replenishment of ATP reserves is required. ATP recovery occurs under anaerobic conditions- due to the breakdown of creatine phosphate (CrP) and glucose (glycolysis reaction), under aerobic conditions- due to the oxidation reactions of fats and carbohydrates.
Fast recovery ATP occurs in thousandths of a second due to the decay of KrF: ADP + KrF = ATP + Kr. This energy generation path achieves the greatest efficiency by 5 - 6 seconds work, but then the reserves of the KrF are exhausted, because there are also few of them (about 30 mmol/l).
The slow recovery of ATP under anaerobic conditions is provided by the energy of the breakdown of glucose (released from glycogen) - the reaction of glycolysis with the eventual formation of lactic acid (lactate) and the reduction of two ATP molecules. This reaction reaches its greatest power towards the end 1- th minutes of work. This path of energy generation is of particular importance when high power work that continues from 20 from to 1 – 2 min (for example, when running at medium distances), as well as with a sharp increase in the power of longer and less powerful work (finishing accelerations when running at long distances) and with a lack of oxygen during static work . Limiting the use of carbohydrates is not associated with a decrease in glycogen (glucose) reserves in the muscles and liver, but with inhibition of the glycolysis reaction by excess lactic acid accumulated in the muscles.
Oxidation reactions provide energy for muscle work under conditions of sufficient oxygen supply to the body, i.e. during aerobic work lasting more than 2 – 3 min . Oxygen delivery reaches the required level after sufficient deployment of the functions of the body’s oxygen transport systems (respiratory, cardiovascular and blood systems). An important indicator of power aerobic processes is the maximum amount of oxygen entering the body in 1 minute - the maximum oxygen consumption ( IPC ). This value depends on the individual capabilities of each person. In untrained individuals, about 2.5–3 liters of O2 are delivered to the working muscles per minute, and in highly qualified athletes (skiers, swimmers, stayers, etc.) it reaches 5–6 liters and even 7 liters per minute.
With significant work power and a huge need for oxygen, the main substrate of oxidation in most sports exercises is carbohydrates , because their oxidation requires much less oxygen than the oxidation of fats. When using one molecule of glucose (C 6 H 12 O 6), obtained from glycogen, 38 molecules of ATP are formed, i.e. The aerobic pathway of energy production provides many times more ATP production for the same carbohydrate consumption than the anaerobic pathway. Lactic acid does not accumulate in these reactions, and the intermediate product - pyruvic acid - is immediately oxidized to the final metabolic products - CO 2 and H 2 O.
Fats are used as a source of energy in a state of motor rest, during any work of relatively low power (requiring up to 50% of the maximum capacity) and during very long endurance work (requiring about 70 - 80% of the maximum capacity). Among all energy sources, fats have the greatest energy capacity : when 1 mole of ATP is consumed, about 10 kcal of energy is released, 1 mole of CrP - about 10.5 kcal, 1 mole of glucose during anaerobic breakdown - about 50 kcal, and when 1 mole of glucose is oxidized under aerobic conditions - about 700 kcal, during oxidation 1 mole of fat – 2,400 kcal. However, the use of fats during high-power work is limited by the difficulty of delivering oxygen to working tissues.
Muscle work is accompanied by the release of heat. Heat generation occurs at the moment of muscle contraction - initial heat generation (it is only one thousandth of all energy expenditure) and during the recovery period - delayed heat generation.
Under normal conditions, when muscles work, heat losses account for about 80% of all energy expenditure. To assess the efficiency of mechanical work of a muscle, the coefficient of performance (efficiency) is calculated. The efficiency value shows what part of the expended energy is used to perform the mechanical work of the muscle. It is calculated using the formula
efficiency = [A: (E - e)] 100%,
where A is the energy spent on useful work;
E – total energy consumption;
e – energy consumption at rest for a time equal to the duration of work.
For an untrained person, the efficiency is approximately 20%, for an athlete - 30 - 35%, i.e. the muscle uses 20–35% of chemical energy for movement, the rest in the form of heat is transferred by the blood to other tissues and evenly warms the body. That is why in the cold a person tries to move more - he warms himself up with muscle energy. Small involuntary muscle contractions cause trembling - the body increases heat production.
When walking, the greatest efficiency is observed at a speed of 3.6 - 4.8 km/h, when pedaling on a bicycle ergometer - with a cycle duration of about 1 second. With an increase in work power and the inclusion of “unnecessary” muscles, efficiency decreases. During static work, since A = 0, work efficiency is assessed by the duration of maintained muscle tension.
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Self-study materials
Questions for the colloquium and for self-control
1. What types of muscles do you know in vertebrates and humans?
2. Name the functions of skeletal muscles.
3. List the neurons that innervate skeletal muscles.
4. What is the functional unit of muscle?
5. What's included motor unit(DE)?
6. What is called the motoneuron pool?
7. Characterize large and small DUs.
8. What is Henneman's rule?
9. Describe the structure of muscle fiber.
10. How are myofibrils structured?
11. What is a sarcomere?
12. How can you explain that at rest the muscle has a striated appearance in a light microscope?
13. Describe the structure of actin and myosin filaments.
14. What is the role of the action potential in the occurrence of muscle contraction?
15. Describe the mechanism of contraction and relaxation of muscle fiber.
16. Who discovered the enzymatic activity of myosin?
17. Indicate the sequence of events leading to contraction and then relaxation of the muscle fiber.
18. What is the role of ATP in the mechanisms of muscle contraction?
19. List the phases of a single muscle contraction.
20. In what cases does the summation of abbreviations occur? What is tetanus?
21. What forms of tetanus do you know?
22. What does the contraction of a whole muscle depend on?
23. What is the electromyography method?
24. What factors does the EMG amplitude depend on?
25. What is muscle strength and what morphological and physiological factors does it depend on?
26. List the types of muscle fibers. Give their characteristics.
27. Name the modes of muscle function.
28. Describe the energetics of muscle contraction.