The maximum level of oxygen consumption characterizes the power of aerobic energy supply processes. The maximum oxygen debt reflects the capacity of anaerobic processes. Below in fig. 4 shows the dynamics of the increase in the level of oxygen consumption Ro/t, l / min during operation for 4 minutes and during subsequent recovery for 30 - 40 minutes. The highest consumption level at the end of the exercise will correspond to the maximum working level of oxygen consumption. The total oxygen consumption during recovery is equal to the oxygen debt.
Rice. 8The level of oxygen consumption during exercise (4 min) and recovery (up to 30 - 40 min)
The sum of oxygen consumption during work and recovery determines the athlete's energy costs and constitutes the oxygen demand.
RO 2 = VO 2+S DO 2, l.
In turn, the oxygen debt is equal to the sum of the alactate and lactate fractions
S DO 2 = DO 2 al+ DO 2 lact, l.
The level of oxygen demand will be
RO 2 / t = VO 2 / t + Σ DO 2 /t, l/min.
The dynamics of oxygen consumption during work can be represented by a two-component exponential equation with a limit value equal to the maximum operating level for this exercise The decrease in intake during recovery can also be expressed as an exponential function with a faster alactate and slower dactate fraction.
Various methods are used to determine the maximum level of oxygen consumption:
1) the method of single ultimate load for 5 - 6 minutes,
2) the method of repeated exercises with increasing load until the maximum aerobic performance is reached,
3) the method of stepwise increase in load during a single exercise,
4) the method of continuous linear increase in load during a single exercise. Other methods are also used.
It should be noted that only in the first method it is possible to accurately determine the external work. The latter is important for determining the relationship with the achievements of the athlete.
The maximum level of oxygen consumption depends on the performance of the heart and the arteriovenous difference in blood oxygen saturation.
VO 2 /t max=Q(A-B)= SV HR(A-B), (8)
where VO2/tmax is the maximum level of oxygen consumption, l/min,
Q - performance of the heart, l / min,
(A - B) - arterio-venous difference in blood oxygen saturation, ml O2 / 100 ml of blood,
SV - stroke volume of the heart, ml / beats,
HR - heart rate, beats/min.
It is known that the performance of the heart in sports activities ranges from 20 - 30 l / min to 40 l / min, stroke volume - from 130 to 200 ml / beats, heart rate reaches 200 beats / min and more. With intense exercise, the arterio-venous difference reaches 15 - 20 O2 ml / 100 ml of blood.
Thus, the level of aerobic energy productivity is characterized by two main factors: circulatory mechanisms and respiration.
Breathing is divided into external and tissue. In turn, these indicators depend on a number of factors of the oxygen capacity of the blood, the rate of diffusion of O2 from the tissue, the vital capacity of the blood, the depth and frequency of breathing, the maximum ventilation of the lungs, the diffusion capacity of the lungs, the percentage of oxygen used, the structure and number of metachondria, the reserves of energy substrates, power of oxidative enzymes, muscle capillarization, volumetric blood flow velocity in tissues, acid-base balance of blood, etc.
Currently, there are numerous data in the literature on the maximum oxygen consumption and its values per unit of body mass in athletes of various specializations. The highest values of maximum oxygen consumption up to 6.7 l/min are observed in cross-country skiers and rowers in rowing. The high values of skiers are largely due to the fact that they compete and train on rough terrain with more ups and downs. Rowers with a high own body weight, due to the design of the boat, develop high power at a distance of 2000 m.
In running exercises, in swimming, in skating and cycling the maximum consumption level is in the range of 5.2 - 5.6 l / min. In terms of oxygen consumption per unit of body weight, the highest values are observed in skiers and runners up to 84 ml/kg/min. For rowers, this value is 67 ml / kg / min due to the fact that their body weight is usually in the range of 90 - 100 kg or more. Relatively low values are also observed in runners and sprint skaters. It should be borne in mind that in swimming and rowing, the level of oxygen consumption per unit of weight is less important than in other sports, since the exercise is performed in water, where streamlining and buoyancy are not essential, but streamlining and buoyancy.
Record levels of oxygen consumption are observed in ski racers up to 7.41 l/min and up to 94 ml/kg/min.
Maximum oxygen debt determined after repeated high-intensity exercise (usually above 95 - 97% of top speed on the cut). IN sports swimming such exercises can be distances of 4 x 50 m with a rest of 15 - 30 s, in running 4 x 400 m, on a bicycle ergometer, repeated exercises lasting up to 60 s. In all cases, the exercises are performed to failure, the duration of repeated exercises does not exceed 60 s, with an increase in rest, the intensity of the exercises increases.
Oxygen debt is determined by analyzing the gas volumes withdrawn during post-exercise recovery. The sizes of gas incomes are determined by subtracting the value of O2 from the oxygen consumption - the consumption of rest. The latter is determined after 30 minutes of rest before exercise at rest while sitting (SMR-sitting metabolic rate), all measurements of gas volumes are reduced to STPD. The calculation of the value of the total oxygen debt, its alactate and lactate fractions is carried out by analyzing the dependence "level of O2 arrival - recovery time" and solving a biexponential equation. It should be borne in mind that since the main lactate fraction of oxygen debt has a high correlation with the concentration of lactic acid in the blood after exercise (up to 0.95 and above), in sports practice, blood lactate is used to assess the anaerobic capacity of an athlete. The latter procedure is much simpler, more convenient and requires less time and equipment.
Anaerobic energy productivity depends on a number of factors: the level of development of compensatory mechanisms and buffer systems that allow you to perform hard work in conditions of a shift in the internal environment (in the direction of acidosis) and prevent this shift; efficiency (power) of anaerobic enzymatic systems; stock in the muscles of energy systems; adaptation of an athlete to exercise in conditions of oxygen debt.
The highest values of oxygen debt were obtained after running four times 400 m with shortening rest - up to 26.26 l, after swimming four times 50 m with a rest of 15 s - up to 14.43 l, on a bicycle ergometer after repeated high-intensity exercises - up to 8.28 l / 406,505/. In table. 10 shows the values of maximum oxygen consumption, oxygen debt and its fractions according to the examination of 80 swimmers (age - 16.7 1.75 years, body length 174.6 6.92 cm, body weight 66.97 9.4 kg) and 78 rowers (age 22.9 3.66 years, body length 187.41 4.21 cm, weight 86.49 5.6 kg). Energy indicators for skaters and runners are given according to N. I. Volkov and V. S. Ivanov.
Table 5
Average values of the maximum level of oxygen consumption, oxygen debt and its fractions in cyclic types sport among athletes with achievements different levels
|
Kind of sport |
Energy indicators |
MSMK |
discharge |
discharge |
||
|
athletics |
V¢ O 2max, l/min S DO 2,l D O2 al, l D O2 lact, l |
|||||
|
Skating |
V¢ O 2max, l/min S D O 2,l D O2 al,l D O2 lac t ,l |
|||||
|
Swimming |
V¢ O 2,max l/min S D O 2,l D O2 al,l D O2 lac t ,l |
|||||
|
Academic |
V¢ O 2,max l/min S D O 2,l D O2 al,l |
|||||
|
D O2 lact,l |
It should be noted that athletes of various qualifications have high values of the lactate fraction of oxygen debt. At the same time, the alactic fraction in all types of exercises does not have such a clear difference.
A high statistical connection of the considered two main energy indicators with achievements at distances was noted. different lengths with significant in volume and stretched in qualification groupings. In swimmers, the greatest relationship between the maximum level of oxygen consumption is observed with achievements at 200 m - 0.822, total oxygen debt per 100 m - 0.766, lactate and alactate fractions with results at 50 m (Table 11).
Tables 6
Correlation coefficients between energy indicators and swimming speed at distances of various lengths (n = 80, at р 0.05 r = 0.22)
|
Energy Indicators |
Distances, m |
|||
IN process muscle work the oxygen supply of the body, phosphagens (ATP and CRF), carbohydrates (muscle and liver glycogen, blood glucose) and fats are consumed. After work, they are restored. The exception is fats, recovery of which may not be.
IN the restorative processes that occur in the body after work find their energy reflection in the increased (p "compared to the pre-working state) oxygen consumption - oxygen debt (see Fig. 12). According to the original theory of A. Hull (1922), oxygen debt is excess O2 consumption above the pre-workout resting level, which provides energy for the body to restore to the pre-working state, including the restoration of energy reserves consumed during work and the elimination of lactic acid.The rate of O2 consumption after work decreases exponentially: during the first 2-3 minutes very quickly (rapid , or lactate, component of oxygen debt), and then more slowly (slow, or lactate, component of oxygen debt), until it reaches (after 30-60 minutes) a constant value close to pre-working.
P After operation with a capacity of up to 60% of the MIC, the oxygen debt does not much exceed the oxygen deficit. After more intense exercise, the oxygen debt significantly exceeds the oxygen deficit, and the more, the higher the power of work (Fig. 24).B The fast (alactic) component of O2-debt is associated mainly with the use of O2 for the rapid recovery of high-energy phosphagens consumed during work in working muscles, as well as with the restoration of normal O2 content in venous blood and with the saturation of myoglobin with oxygen.
M The slow (lactate) component of O2-debt is associated with many factors. To a large extent, it is associated with the post-working elimination of lactate from the blood and tissue fluids. In this case, oxygen is used in oxidative reactions that ensure the resynthesis of glycogen from blood lactate (mainly in the liver and partly in the kidneys) and the oxidation of lactate in the heart and skeletal muscles. In addition, a long-term increase in O2 consumption is associated with the need to maintain an increased activity of the respiratory and cardiovascular systems during the recovery period, increased metabolism and other processes that are caused by a long-term increased activity of the sympathetic nervous and hormonal systems, increased body temperature, which also slowly decrease by throughout the recovery period.
Restoration of oxygen reserves. Oxygen is found in the muscles in the form of a chemical bond with myoglobin. These stocks are very small: each kilogram muscle mass contains about 11 ml of O2. Consequently, the total reserves of "muscle" oxygen (per 40 kg of muscle mass in athletes) do not exceed 0.5 liters. In the process of muscular work, it can be quickly consumed, and after work it can be quickly restored. The rate of restoration of oxygen reserves depends only on its delivery to the muscles.
WITH once after the cessation of work, the arterial blood passing through the muscles has a high partial tension (content) of O2, so that the restoration of O2-myoglobin occurs, probably, in a few seconds. The oxygen consumed in this case constitutes a certain part of the fast fraction of oxygen debt, which also includes a small amount of O2 (up to 0.2 l), which goes to replenish its normal content in venous blood.
T Thus, within a few seconds after the cessation of work, oxygen "reserves" in the muscles and blood are restored. The partial tension of O2 in the alveolar air and arterial blood not only reaches the pre-working level, but also exceeds it. The content of O2 in the venous blood flowing from the working muscles and other active organs and tissues of the body is also quickly restored, which indicates their sufficient oxygen supply in the post-work period. Therefore, there is no physiological reason to use breathing with pure oxygen or a mixture with a high content oxygen after work to speed up recovery processes.
Recovery of phosphagens (ATP and CRF). Phosphagens, especially ATP, are restored very quickly (Fig. 25). Already within 30 s after the cessation of work, up to 70% of the consumed phosphagens are restored, and their complete replenishment ends in a few minutes, and almost exclusively due to the energy of aerobic metabolism, i.e. due to oxygen consumed in the fast phase of O2-debt. Indeed, if immediately after work, the working limb is tourniqueted and thus deprives the muscles of oxygen delivered with the blood, then the restoration of CRF will not occur.How more consumption of phosphagens per. operating time, the more O2 is required to restore them (to restore 1 mole of ATP, 3.45 liters of O2 are needed). The value of the fast (alactic) fraction of O2-debt is directly related to the degree of decrease in phosphagens in the muscles by the end of work. Therefore, this value indicates the amount of phosphagens consumed during the operation.
At untrained men, the maximum value of the fast fraction of O2-debt reaches 2-3 liters. Particularly large values of this indicator were registered among representatives of speed-strength sports (up to 7 liters in 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.
Recovery of glycogen. 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, O2-Debt fraction. However, it is now established that the restoration of glycogen in the muscles can last up to 2-3 days.
WITH The rate of glycogen recovery and the amount of its recoverable 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 recovery 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 the daily calorie content), 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 much higher than usual. In the future, the amount of glycogen in the working muscles and in the liver continues to increase, and 2-3 days after the "exhausting" load, it can exceed the pre-working 1.5-3 times - the phenomenon of supercompensation (see Fig. 21, curve 2).
At daily intense and long training sessions, the glycogen content in the working muscles and liver is significantly reduced from day to day, since with a normal diet, even a daily break between workouts is not enough to fully restore glycogen. Increasing the content of carbohydrates in the athlete's diet can ensure a complete restoration of the body's carbohydrate resources by the next training session (Fig. 26). At elimination of lactic acid. During the recovery period, lactic acid is eliminated from the working muscles, blood and tissue fluid, and the faster, the less lactic acid was formed during work. Important role plays also after-work mode. So, after a maximum load, it takes 60-90 minutes to completely eliminate the accumulated lactic acid in conditions of complete rest - sitting or lying down (passive recovery). However, if light work (active recovery) is performed after such a load, then the elimination of lactic acid occurs much faster. In untrained people, the optimal intensity of the "restoring" load is approximately 30-45% of the IPC (for example, jogging), as well. in well-trained athletes - 50-60% of the IPC, with a total duration of approximately 20 minutes (Fig. 27).WITH There are four main ways to eliminate lactic acid: 1) oxidation to CO2 and SO (this eliminates approximately 70% of all accumulated lactic acid); 2) conversion to glycogen (in muscles and liver) and glucose (in the liver) - about 20%; 3) conversion to proteins (less than 10%); 4) removal with urine and sweat (1-2%). With active recovery, the proportion of lactic acid eliminated aerobically increases. Although lactic acid oxidation can occur in a variety of organs and tissues (skeletal muscles, heart muscle, liver, kidneys, etc.), most of it is oxidized in skeletal muscles (especially their slow fibers). This makes it clear why light work (which involves mainly slow muscle fibers) contributes to faster elimination of lactate after heavy loads.
W A significant part of the slow (lactate) fraction of O2-debt is associated with the elimination of lactic acid. The more intense the load, the greater this fraction. In untrained people, it reaches a maximum of 5-10 liters, in athletes, especially among representatives of speed-strength sports, it reaches 15-20 liters. Its duration is about an hour. The magnitude and duration of the lactate fraction of O2-debt decrease with active recovery.
OXYGEN CONSUMPTION AND OXYGEN DEBT OXYGEN CONSUMPTION AND OXYGEN DEBT - Lecture, section Sport, Course of lectures on the subject Physiological basis physical culture and sports, teaching aid The term Oxygen Consumption Denotes the Amount of O2 Absorbed. The term oxygen consumption refers to the amount of O 2 . absorbed by the body over a certain period of time (usually within 1 minute). At rest and with moderate muscle activity, i.e. when ATP resynthesis is based only on aerobic processes (oxidative phosphorylation), O 2 consumption corresponds to the oxygen demand of the body. As the intensity of activity increases (for example, with an increase in the power of muscle work), anaerobic processes are switched on for a sufficiently effective resynthesis of ATP. This is due not only to the fact that it is not possible to supply the working muscles with oxygen sufficiently. This is mainly due to the fact that oxidative phosphorylation is a relatively slow process and it does not have time to ensure a sufficient rate of ATP resynthesis during intense muscle activity. Therefore, the activation of faster anaerobic processes is necessary. In this regard, after the end of work, it becomes necessary to maintain the consumption of O2 for a certain period of time for elevated level to resynthesize spent amounts of creatine phosphate and eliminate lactic acid. The term "oxygen debt" was proposed by the English scientist A. Hill to denote the amount of oxygen that must be additionally consumed after work is completed in order to cover the costs of anaerobic energy processes due to oxidative phosphorylation. The oxygen demand during work thus consists of the sum of O 2 consumption during work and the oxygen debt. The need for anaerobic processes almost always occurs at the beginning of muscle work, since ATP consumption increases more rapidly than oxidative phosphorylation unfolds. Therefore, ATP resynthesis at the very beginning of muscle work is provided by anaerobic processes. This leads to an oxygen deficit at the beginning of work, which must be covered by an additional increase in oxidative processes after the end of work or during the work itself. The latter is possible with prolonged operation of moderate power. Oxygen debt includes two components (R. Margaria): a) alactic oxygen debt is the amount of O 2 . which must be spent for the resynthesis of ATP and CP and replenishment of the tissue oxygen reservoir (oxygen bound in muscle tissue with myoglobin), b) lactate oxygen debt is the amount of O 2. which is necessary to eliminate the lactic acid accumulated during operation. The elimination of lactic acid consists in the oxidation of one part of it to H 2 O and CO 2 and in the resynthesis of glycogen from the rest. Alactate oxygen debt is eliminated in the first minutes after the end of work. Elimination of lactate oxygen debt can last 30 minutes or more.
Oxygen consumption (OC) is an indicator that reflects the functional state of the cardiovascular and respiratory systems.
With an increase in the intensity of metabolic processes during physical exertion, a significant increase in oxygen consumption is necessary. This places increased demands on the function of the cardiovascular and respiratory systems.
At the beginning of dynamic work of submaximal power, oxygen consumption increases and after a few minutes reaches a steady state. Cardiovascular and respiratory system are put into operation gradually, with some delay. Therefore, at the beginning of work, oxygen deficiency increases. It persists until the end of the load and stimulates the activation of a number of mechanisms that provide the necessary changes in hemodynamics.
Under conditions of steady state, the body's consumption of oxygen is fully satisfied, the amount of lactate in the arterial blood does not increase, and ventilation of the lungs, heart rate, and atmospheric pressure also do not change. The time to reach a steady state depends on the degree of preload, intensity, work of the athlete. If the load exceeds 50% of the maximum aerobic power, then a steady state occurs within 2-4 minutes. With increasing load, the time to stabilize the level of oxygen consumption increases, while there is a slow increase in ventilation of the lungs, heart rate. At the same time, the accumulation of lactic acid in the arterial blood begins. After the end of the load, oxygen consumption gradually decreases and returns to the initial level of the amount of oxygen consumed in excess of the basal metabolic rate in the recovery period, called oxygen debt (OD).
Oxygen debt consists of 4 components:
Aerobic Elimination of Anaerobic Metabolism Products (initial KD)
Increase in oxygen debt by the heart muscle and respiratory muscles (to restore the initial heart rate and respiratory rate)
An increase in tissue oxygen consumption depending on a temporary increase in body temperature
Replenishment of myoglobin oxygen
The size of the oxygen debt depends on the amount of effort and training of the athlete. With a maximum load lasting 1–2 minutes, an untrained person has a debt of 3–5 liters, and an athlete has 15 liters or more. Maximum oxygen debt is a measure of the so-called anaerobic capacity. It should be borne in mind that CA rather characterizes the total capacity of anaerobic processes, that is, the total amount of work done at maximum effort, and not the ability to develop maximum power.
Maximum oxygen consumption
Oxygen consumption increases in proportion to the increase in load, however, there comes a limit at which a further increase in load is no longer accompanied by an increase in AC. This level is called maximum oxygen consumption or oxygen limit.
Maximum oxygen uptake is the maximum amount of oxygen that can be delivered to working muscles in 1 minute.
The maximum oxygen consumption depends on the mass of the working muscles and the state of the oxygen transport systems, respiratory and cardiac performance, and peripheral circulation. The value of the BMD is associated with heart rate, stroke volume, arterio-venous difference - the difference in oxygen content between arterial and venous blood (AVR)
MPK = HR * WOK * AVRO2
The maximum oxygen consumption is determined in liters per minute. IN childhood it increases in proportion to height and weight. In men, it reaches its maximum level by 18-20 years. Starting from the age of 25-30, it steadily decreases.
On average, the maximum oxygen consumption is 2-3 l / min, and for athletes 4-7 l / min
For rate physical condition a person’s oxygen pulse is determined - the ratio of oxygen consumption per minute to the pulse rate for the same minute, that is, the number of milliliters of oxygen that is delivered in one heart contraction. This indicator characterizes the efficiency of the work of the heart. The less the oxygen pulse increases, the more efficient the hemodynamics, the lower the heart rate the required amount of oxygen is delivered.
At rest, the CP is 3.5-4 ml, and with intense physical activity, accompanied by oxygen consumption of 3 l / min, it increases to 16-18 ml.
11. biochemical characteristics of muscle activity of different power (zone of maximum and submaximal power)
Relative Power Zones of Muscular Work
Currently, various classifications of the power of muscle activity are accepted. One of them is the B.C. classification. Farfel, based on the position that the power of the physical activity is due to the ratio between the three main ATP resynthesis pathways that function in the muscles during work. According to this classification, four zones of relative power of muscular work are distinguished: maximum, submaximal, high and moderate power.
Work in the zone maximum power may continue for 15-20 s. The main source of ATP under these conditions is creatine phosphate. Only at the end of the work, the creatine phosphate reaction is replaced by glycolysis. An example exercise performed in the maximum power zone is running on short distances, long jump and high jump, some gymnastic exercises, lifting the bar, etc.
Work in the zone submaximal power has a duration of up to 5 minutes. The leading mechanism of ATP resynthesis is glycolytic. At the beginning of work, until glycolysis has reached its maximum rate, the formation of ATP is due to creatine phosphate, and at the end of work, glycolysis begins to be replaced by tissue respiration. Work in the zone of submaximal power is characterized by the highest oxygen debt - up to 20 liters. Examples of exercise in this power zone are middle distance running, short distance swimming, bicycle racing on the track, skating on sprint distances and etc.
12. biochemical characteristics of muscle activity of various power (zone of high and moderate power)
Work in the zone high power has a maximum duration of up to 30 minutes. Work in this zone is characterized by approximately the same contribution of glycolysis and tissue respiration. The creatine phosphate pathway of ATP resynthesis functions only at the very beginning of work, and therefore its share in the total energy supply of this work is small. An example of exercise in this power zone is a 5000-hour run in skating for stayer distances, ski race cross-country, intermediate and long distances and etc.
Work in the zone moderate power lasts over 30 minutes. Energy supply of muscle activity occurs mainly in the aerobic way. An example of such power is marathon run, athletics cross, race walking, road cycling, long-distance cross-country skiing, hiking, etc.
In acyclic and situational sports, the power of the work performed changes many times. So, for a football player, running at a moderate speed alternates with running for short distances at a sprint speed; you can also find such segments of the game when the power of work is significantly reduced. Such examples can be given in relation to many other sports.
However, in a number of sports disciplines, physical loads related to a certain power zone still prevail. So, the physical work of skiers is usually performed with high or moderate power, and in weightlifting, maximum and submaximal loads are used.
Therefore, in the preparation of athletes, it is necessary to apply training loads, developing the path of ATP resynthesis, which is the leading one in the energy supply of work in the relative power zone characteristic of this sport.
Aerobic system is the oxidation of nutrients in the mitochondria for energy. This means that the glucose, fatty acids and amino acids of food, as shown on the left in the figure, after some intermediate processing, combine with oxygen, releasing a huge amount of energy, which is used to convert AMP and ADP to ATP.
Aerobic mechanism comparison of obtaining energy with the glycogen-lactic acid system and the phosphagenic system, according to the relative maximum rate of power generation, expressed in moles of ATP generated per minute, gives the following result.
Thus, one can easily understand that phosphagenic system use muscles for bursts of power lasting a few seconds, but the aerobic system is essential for sustained athletic activity. Between them is the glycogen-lactic acid system, which is especially important for providing additional power during intermediate loads (for example, races of 200 and 800 m).
What energy systems used in different sports? Knowing the power physical activity and its duration for different types sports, it is easy to understand which of the energy systems is used for each of them.
Recovery of muscle metabolic systems after physical activity. Just as the energy of phosphocreatine can be used to restore ATP, the energy of the glycogen-lactic acid system can be used to restore both phosphocreatine and ATP. The energy of oxidative metabolism can restore all other systems, ATP, phosphocreatine and the glycogen-lactic acid system.
Recovery of lactic acid means simply the removal of its excess accumulated in all body fluids. This is especially important since lactic acid causes extreme fatigue. Given sufficient energy generated by oxidative metabolism, lactic acid is removed in two ways: (1) a small portion of lactic acid is converted back to pyruvic acid and then undergoes oxidative metabolism in body tissues; (2) the rest of the lactic acid is converted back to glucose, mainly in the liver. Glucose, in turn, is used to replenish muscle glycogen stores.
Recovery of the aerobic system after physical activity. Even in the early stages of severe physical work a person's ability to synthesize energy aerobically is partially reduced. This is due to two effects: (1) the so-called oxygen debt; (2) depletion of muscle glycogen stores.
oxygen debt. Normally, the body contains approximately 2 liters of oxygen in reserve, which can be used for aerobic metabolism even without inhaling new portions of oxygen. This supply of oxygen includes: (1) 0.5 liters in the air of the lungs; (2) 0.25 L dissolved in body fluids; (3) 1 L associated with blood hemoglobin; (4) 0.3L, which are stored in themselves muscle fibers, mainly in combination with myoglobin - a substance that is similar to hemoglobin and binds oxygen like it.
During heavy physical work almost the entire supply of oxygen is used for aerobic metabolism for about 1 min. Then, after the end of physical activity, this reserve must be replenished by inhaling additional oxygen compared to resting needs. In addition, about 9 liters of oxygen must be used to restore the phosphagenic system and lactic acid. The extra oxygen that must be replaced is called the oxygen debt (about 11.5 liters).
The figure illustrates principle of oxygen debt. During the first 4 minutes, a person performs hard physical work, and the rate of oxygen consumption increases by more than 15 times. Then, after the end of physical work, oxygen consumption still remains above the norm, and at first it is much higher, while the phosphagenic system is restored and the oxygen supply is replenished as part of the oxygen debt, and over the next 40 minutes lactic acid is removed more slowly. The early part of the oxygen debt, which amounts to 3.5 liters, is called alactacid oxygen debt (not related to lactic acid). The late part of the debt, which is approximately 8 liters of oxygen, is called lactic acid oxygen debt (associated with the removal of lactic acid).
