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. Figure 4 shows the dynamics of the increase in oxygen consumption level Ro/t, l/min during operation for 4 minutes and during subsequent recovery for 30 - 40 minutes. The highest level of consumption 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. 8Level of oxygen consumption during exercise (4 min) and recovery (up to 30 - 40 min)
The amount of oxygen consumption during work and recovery determines the athlete’s energy expenditure and constitutes the oxygen demand.
R.O. 2 = V.O. 2+S DO 2, l.
In turn, the oxygen debt is equal to the sum of the alactic and lactate fractions
S DO 2 = DO 2 al+ DO 2 lact, l.
The oxygen demand level will be
R.O. 2 / t = V.O. 2/t+Σ DO 2 /t, l/min.
The dynamics of oxygen consumption during operation 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 by an exponential function with a faster alactate and a slower dactate fraction.
Various methods are used to determine the maximum level of oxygen consumption:
1) single maximum load method for 5 - 6 minutes,
2) the method of repeated exercises with increasing load until maximum aerobic performance is achieved,
3) the method of stepwise increasing the load during a single exercise,
4) 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 is it possible to determine external work quite accurately. The latter is important for determining the relationship with the athlete’s achievements.
The maximum level of oxygen consumption depends on the performance of the heart and the arteriovenous difference in blood oxygen saturation
V.O. 2 /t max = Q (A - B) = SV HR(A-B), (8)
where VO2/tmax is the maximum level of oxygen consumption, l/min,
Q - heart performance, l/min,
(A - B) - arteriovenous difference in blood oxygen saturation, ml O2 / 100 ml of blood,
SV - stroke volume of the heart, ml/beat.,
HR - heart rate, beats/min.
It is known that cardiac performance in sports activities ranges from 20 - 30 l/min to 40 l/min, stroke volume - from 130 to 200 ml/beat, heart rate reaches 200 beats/min and more. With intense exercise, the arteriovenous 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: the oxygen capacity of the blood, the rate of O2 diffusion from the tissue, the vital capacity of the blood, the depth and frequency of respiration, maximum ventilation of the lungs, the diffusion capacity of the lungs, the percentage of oxygen used, the structure and number of metachondria, reserves of energy substrates, the power of oxidative enzymes, muscle capillarization, volumetric blood flow velocity in tissues, acid-base balance of blood, etc.
The literature currently contains numerous data on the maximum oxygen consumption and its values per unit of body weight 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. The higher values among skiers are due in large part to the fact that they compete and train on rough terrain with more uphills and downhills. Rowers at high dead weight Due to the design of the boat, the bodies develop high power at a distance of 2000 m.
In running exercises, swimming, speed 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-stayers 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 it is not body weight that is 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 maximum speed on the segment). IN sport 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 seconds, and with increasing rest, the intensity of the exercises increases.
Oxygen debt is determined by analyzing gas volumes taken during recovery from exercise. The size of gas inflows is determined by subtracting the O2 value - rest consumption - from oxygen consumption. 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. Calculation of the total oxygen debt, its alactic and lactate fractions is carried out by analyzing the relationship “level of O2 arrival - recovery time” and solving the 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 higher), then in sports practice, determination of blood lactate is used to assess the anaerobic capabilities 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 performing strenuous work in conditions of a shift in the internal environment (towards acidosis) and preventing this shift; efficiency (power) of anaerobic enzymatic systems; reserves of energy systems in muscles; adaptation of an athlete to performing exercises in conditions of oxygen debt.
The highest values of oxygen debt were obtained after running 400 m four times with shortening rest - up to 26.26 l, after swimming 50 m four times 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 Table 10 shows the values of maximum oxygen consumption, oxygen debt and its fractions according to a survey 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 sports among athletes with achievements different levels
|
Type of sport |
Energy indicators |
MSMK |
discharge |
discharge |
||
|
Athletics |
V¢ O 2max, l/min SDO 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 track and field 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 between the considered two main energy indicators and achievements at distances was noted different lengths with groups of significant volume and extensive qualifications. In swimmers, the greatest correlation between the maximum level of oxygen consumption is observed with achievements at 200 m - 0.822, total oxygen debt at 100 m - 0.766, lactate and alactate fractions with results at 50 m (Table 11).
Table 6
Correlation coefficients between energy indicators and swimming speed at distances of various lengths (n = 80, at p 0.05 r = 0.22)
|
Energy Indicators |
Distances, m |
|||
IN process muscle work the body's oxygen supply, phosphagens (ATP and CrF), carbohydrates (muscle and liver glycogen, blood glucose) and fats are consumed. After work they are restored. The exception is fats, which may not be restored.
IN the recovery processes occurring in the body after work are reflected energetically in increased (compared to the pre-work state) oxygen consumption - oxygen debt (see Fig. 12). According to the original theory of A. Hill (1922), oxygen debt is excess O2 consumption above the pre-working resting level, which provides the body with energy to restore to the pre-working state, including the restoration of energy reserves expended 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 (fast. , 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 the pre-working value.
P After operating at a power of up to 60% of the MOC, the oxygen debt does not significantly exceed the oxygen deficit. After more intense exercise, the oxygen debt significantly exceeds the oxygen deficit, and the greater the higher the work power (Fig. 24).B The fast (alactate) component of O2 debt is associated mainly with the use of O2 for the rapid restoration of high-energy phosphagens consumed during work in the working muscles, as well as with the restoration of the normal O2 content in the 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-work 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 increased activity of the respiratory and cardiovascular systems during the recovery period, increased metabolism and other processes that are caused by long-term increased activity of the sympathetic nervous and hormonal systems, increased body temperature, which also slowly decrease by throughout the recovery period.
Restoring oxygen reserves. Oxygen is found in muscles in the form of a chemical bond with myoglobin. These reserves are very small: every kilogram muscle mass contains about 11 ml O2. Consequently, the total reserves of “muscle” oxygen (based on 40 kg of muscle mass in athletes) do not exceed 0.5 liters. During 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 probably occurs within a few seconds. The oxygen consumed in this case constitutes a certain part of the fast fraction of the oxygen debt, which also includes a small volume of O2 (up to 0.2 l), which is used to replenish its normal content in the venous blood.
T Thus, within a few seconds after stopping work, the 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 O2 content in the venous blood flowing from working muscles and other active organs and tissues of the body is also quickly restored, which indicates their sufficient supply of oxygen in the post-working 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.
Restoration 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 more consumption of phosphagens for. operating time, 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 registered 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
WITH The rate of glycogen recovery and the amount of its restored reserves in the muscles and liver depends 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 (see Fig. 21, curve 2).
At daily intensive and long-term training sessions, the glycogen content in the 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 (Fig. 26). U loss of 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. Important role The after-work mode also plays a 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, 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 SHO (this removes 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 faster after heavy exercise.
Z 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 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.
OXYGEN CONSUMPTION AND OXYGEN DEBT OXYGEN CONSUMPTION AND OXYGEN DEBT - Lecture, section Sports, Course of lectures on the subject Physiological basis physical culture and sports, teaching aid The term Oxygen Consumption Indicates 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, when the power of muscle work increases), anaerobic processes are activated for sufficiently effective resynthesis of ATP. This is due not only to the fact that it is not possible to supply working muscles with oxygen sufficiently. This is mainly due to the fact that oxidative phosphorylation is a relatively slow process and does not have time to ensure a sufficient rate of ATP resynthesis during intense muscle activity. Therefore, activation of faster anaerobic processes is necessary. In this regard, after finishing work, it becomes necessary to maintain O2 consumption for a certain period of time. elevated level to resynthesize the expended 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 finishing work in order to cover the costs of anaerobic energy processes through oxidative phosphorylation. The oxygen demand during operation thus consists of the sum of O2 consumption during operation and the oxygen debt. The need for anaerobic processes almost always arises at the beginning of muscle work, since ATP consumption increases more quickly than oxidative phosphorylation develops. Therefore, ATP resynthesis at the very beginning of muscle work is ensured through anaerobic processes. This leads to an oxygen deficiency at the beginning of work, which must be covered by additional strengthening of 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 lactic acid accumulated during operation. The elimination of lactic acid consists of the oxidation of one part of it to H 2 O and CO 2 and the resynthesis of glycogen from the rest. Alactate oxygen debt is eliminated in the first minutes after finishing work. Elimination of lactate oxygen debt can last 30 minutes or more.
Oxygen consumption (OC) is an indicator that reflects functional state cardiovascular and respiratory systems.
With an increase in the intensity of metabolic processes during physical activity, 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 start working 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 steady state conditions, the body's oxygen consumption is completely satisfied, the amount of lactate in the arterial blood does not increase, and ventilation, heart rate, and atmospheric pressure do not change. The time to reach a steady state depends on the degree of preload, intensity, and work of the athlete. If the load exceeds 50% of maximum aerobic power, then steady state occurs within 2–4 minutes. With increasing load, the time to stabilize the level of oxygen consumption increases, while a slow increase in ventilation and heart rate is observed. At the same time, lactic acid begins to accumulate in the arterial blood. After completion of the load, oxygen consumption gradually decreases and returns to the original level of the amount of oxygen consumed above the level of basal metabolism in the recovery period is called oxygen debt (OD).
Oxygen debt consists of 4 components:
Aerobic elimination of products of anaerobic metabolism (initial CD)
Increasing oxygen debt by the heart muscle and respiratory muscles (to restore the initial heart rate and respiratory rate)
Increased oxygen consumption by tissues depending on a temporary increase in body temperature
Replenishment of myoglobin with oxygen
The amount of 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 so-called anaerobic capacity. It should be taken into account that CD rather characterizes the total capacity of anaerobic processes, that is, the total amount of work performed with maximum effort, rather than the ability to develop maximum power
Maximum oxygen consumption
Oxygen consumption increases in proportion to the increase in load, but there comes a limit at which a further increase in load is no longer accompanied by an increase in blood pressure. This level is called the maximum oxygen consumption or oxygen limit.
Maximum oxygen consumption is the maximum amount of oxygen that can be delivered to working muscles within 1 minute.
Maximum oxygen consumption depends on the mass of working muscles and the state of oxygen transport systems, respiratory and cardiac performance, and peripheral circulation. The value of MOC is related to heart rate, stroke volume, arteriovenous difference - the difference in oxygen content between arterial and venous blood (AVR)
MPC=HR*UOK*AVRO2
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 25–30 years, it steadily decreases.
On average, maximum oxygen consumption is 2–3 l/min, and for athletes 4–7 l/min
To assess a person’s physical condition, the oxygen pulse is determined - the ratio of oxygen consumption per minute to the pulse rate in the same minute, that is, the number of milliliters of oxygen that is delivered in one heartbeat. This indicator characterizes the efficiency of the heart. The less the oxygen pulse increases, the more effective the hemodynamics; the lower the heart rate, the required amount of oxygen is delivered.
At rest, 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 varying power (zone of maximum and submaximal power)
Zones of relative power of muscle work
Currently, various classifications of muscle activity power have been adopted. One of them is the B.C. classification. Farfel, based on the position that the power performed physical activity is determined by the relationship between the three main pathways of ATP resynthesis that function in muscles during work. According to this classification, four zones of relative power of muscle work are distinguished: maximum, submaximal, large and moderate power.
Work in the zone maximum power can last for 15-20 s. The main source of ATP under these conditions is creatine phosphate. Only at the end of the work is the creatine phosphate reaction replaced by glycolysis. Example physical exercise performed in the maximum power zone is running short distances, long and high jumps, some gymnastic exercises, lifting the barbell, 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 speed, the formation of ATP occurs due to creatine phosphate, and at the end of work, glycolysis begins to be replaced by tissue respiration. Work in the submaximal power zone is characterized by the highest oxygen debt - Up to 20 liters. Examples of physical activity in this power zone are middle-distance running, short-distance swimming, bicycle racing on the track, ice skating sprint distances etc.
12.biochemical characteristics of muscle activity of varying 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 equal contributions from 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 exercises in this power zone is running at 5000 centimeters, skating at stayer distances, cross-country skiing cross-country, intermediate and intermediate swimming long distances etc.
Work in the zone moderate power lasts over 30 minutes. Energy supply to muscle activity occurs predominantly aerobically. An example of such power operation is marathon running, athletics cross-country, 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, a football player alternates running at a moderate speed with running short distances at a sprint speed; You can also find 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 sports disciplines nevertheless, physical activity related to a certain power zone predominates. Thus, the physical work of skiers is usually performed with high or moderate power, and in weightlifting maximum and submaximal loads are used.
Therefore, when preparing athletes, it is necessary to use training loads, developing the ATP resynthesis pathway, which is the leading one in energy supply for work in the relative power zone characteristic of a given sport.
Aerobic system is the oxidation of nutrients in mitochondria to produce energy. This means that the glucose, fatty acids and amino acids of the food substances, as shown on the left in the figure, after some intermediate processing, combine with oxygen, releasing enormous amounts of energy, which is used to convert AMP and ADP into ATP.
Comparison of the aerobic mechanism energy production with the glycogen-lactic acid system and the phosphagen system according to the relative maximum rate of power generation, expressed in moles of ATP formed per minute, gives the following result.
So it can be easily understood that phosphagen system use muscles for bursts of power lasting a few seconds, but the aerobic system is essential for long-term athletic activity. In between is the glycogen-lactic acid system, which is especially important for providing additional power during intermediate-duration exercises (for example, 200 and 800 m races).
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 energy system is used for each.
Restoration of muscle metabolic systems after physical activity. Just as energy from phosphocreatine can be used to restore ATP, energy from 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.
Lactic acid reduction means simply removing its excess accumulated in all body fluids. This is especially important because lactic acid causes extreme fatigue. If there is sufficient energy generated by oxidative metabolism, the removal of lactic acid occurs in two ways: (1) a small part of the 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 glycogen stores in the muscles.
Restoring 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. The body normally contains approximately 2 liters of stored oxygen, which can be used for aerobic metabolism even without inhaling new 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) 0.3 l, which are stored in the muscle fibers, mainly in combination with myoglobin - a substance that is similar to hemoglobin and, like it, binds oxygen.
During heavy physical work almost the entire oxygen supply is used for aerobic metabolism within about 1 min. Then, after the end of physical activity, this supply must be replaced by inhaling additional oxygen compared to resting requirements. In addition, about 9 liters of oxygen must be spent to restore the phosphagen system and lactic acid. The additional oxygen that must be replaced is called the oxygen debt (about 11.5 L).
The picture illustrates oxygen debt principle. During the first 4 minutes, a person performs heavy 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 normal, and at first it is much higher, while the phosphagen system is restored and the oxygen supply is replaced as part of the oxygen debt, and over the next 40 minutes lactic acid is more slowly removed. The early part of the oxygen debt, the amount of which is 3.5 L, is called alactic oxygen debt (not associated with lactic acid). The later portion of the debt, approximately 8 L of oxygen, is called the lactic oxygen debt (associated with the removal of lactic acid).
