Biochemical Foundations of Human Vital Activity - Volkov N.I., Nesen E.N. 2000

Biochemistry of Sports
Biochemical changes in the body during exercise of varying intensity and duration
Classification of physical exercises according to the nature of biochemical changes during muscular work

Depending on the number of Muscles involved in contraction, physical work is classified into local (involving less than 1/4 of all body muscles), regional, and global (involving more than 3/4 of all body muscles).

Local work (such as pulling a trigger while shooting or moving chess pieces) may cause changes within the working Muscle itself, yet BIOCHEMICAL SHIFTS IN the body as a whole remain negligible.

Regional work (such as elements of various gymnastic exercises or striking a ball from a stationary position) induces much greater biochemical shifts than local muscle work, which depends on the proportion of anaerobic reactions in its energy supply.

Global work (such as walking, running, swimming, cross-country skiing, or ice skating) causes substantial biochemical shifts across all Organs and Tissues of the body. It significantly enhances The activity of the respiratory and cardiovascular systems, improves oxygen delivery to the muscles, and consequently relies on a larger share of aerobic ATP resynthesis for energy.

Metabolic shifts in the body are also influenced by the regime of muscular activity. Two working regimes are distinguished: static and dynamic. A static (isometric) Muscle contraction regime compresses capillaries under high contraction force, thereby impairing the supply of oxygen and nutrients to the muscles. This type of work relies heavily on anaerobic reactions. Conversely, a dynamic (isotonic) work regime ensures a much better supply of oxygen to tissues, as rhythmically contracting muscles act as a kind of pump that forces Blood through the capillaries. Recovery after static work requires dynamic activity rather than rest (for instance, a weightlifter should walk around after a heavy lift to recover more quickly).

Changes in the body's biochemical processes depend on the intensity and duration of the muscular work performed. Furthermore, the higher the intensity—and consequently, the higher The rate of ATP Cleavage—the lower the capacity to meet energy demands through respiratory oxidation processes, and the greater the reliance on anaerobic ATP resynthesis.

As the intensity of the work increases, O₂ consumption and the rate of aerobic energy supply rise to their maximum values. The power output at which maximum oxygen consumption is achieved is termed critical power (W_crit). Up to this critical threshold, any increase in workload is accompanied by a proportional enhancement of aerobic ATP resynthesis processes, whereas beyond it, energy is supplied exclusively through anaerobic processes, The Development of which begins even before the critical power is reached. The exercise intensity at which anaerobic reactions begin to intensify is called the anaerobic threshold (AT). In untrained individuals, the AT occurs at 50% of critical power; in athletes across various disciplines, it is 60–75%; and in endurance specialists, it reaches 85–90%. Once the AT is exceeded, the proportion of anaerobic reactions in the energy supply increases sharply due to a higher rate of Glycolysis. Consequently, glycolysis plays a leading role as a mechanism of energy production at an intensity of 60–85% of the maximum. The power output that yields the peak Development of the glycolytic process is known as exhaustion power (W_exh). The maximum possible power output for a human is designated as maximum anaerobic power (W_max). At this power level, the rate of energy production via the creatine kinase reaction reaches its limit.

Work intensity is inversely proportional to its duration; the greater the intensity, the more rapidly biochemical changes occur, leading to fatigue and cessation of work. Based on work intensity and energy supply mechanisms, all cyclic exercises are divided into four zones according to V. S. Farfel's Classification (1975): maximum, submaximal, high, and moderate. The limit duration of work in the maximum power zone is 25–30 s; in the submaximal power zone, from 30 s to 3–5 min; in the high power zone, from 3–5 to 50 min; and in the moderate power zone, from 50–60 min to 4–5 hours. The main biochemical blood parameters during work across these specific power zones are presented in Table 27, while the orientation and sources of energy supply in each zone, along with their post-work recovery periods, are shown in Table 28.

Class="center">TABLE 27. Dynamics of Biochemical blood parameters during physical loads of varying intensity

TABLE 28. Biochemical characteristics of physical loads in different relative power zones

Work in the maximum power zone is fueled primarily by ATP and PCr, and partially by glycolysis. However, the rate of glycolysis in this zone does not reach its maximum values; consequently, blood lactic acid content typically does not exceed 1.5 g ⋅ L^-1. Blood glucose levels remain largely unchanged compared to resting values (or rise slightly solely due to the pre-start reaction), as liver glycogen mobilization is virtually absent. Oxygen demand may range from 7 to 14 L, while the oxygen debt amounts to 6–12 L, i.e., 90–95% of the oxygen demand.

Energy supply for work in the submaximal power zone is mediated mainly through anaerobic glycolysis, resulting in significant lactic acid accumulation in the blood (its concentration can reach 2.5 g ⋅ L^-1 or more). Oxygen demand during such work can reach 20–40 L, and Energy Expenditure can exceed the maximum of the aerobic energy production mechanism by 4–5 times. Toward the end of the work, the proportion of aerobic reactions in the energy supply increases. The oxygen debt in this power zone is most pronounced in absolute terms (up to 20 L) and accounts for 50–90% of the oxygen demand. Liver glycogen mobilization intensifies, and blood glucose levels can reach 2 g ⋅ L^-1. Driven by anaerobic breakdown products, Cell membrane permeability to proteins increases, leading to elevated blood protein levels and their appearance in the urine, where concentrations reach 1.5%.

During muscular work in the high power zone, aerobic energy sources play the primary role alongside a quite high level of glycolysis development. The proportion of anaerobic processes in energy supply declines rapidly as the duration of the work increases. Under these conditions, oxygen demand can reach 50–150 L, and energy expenditure can exceed the maximum aerobic energy output by 1.5–2 times. Blood lactic acid content is 1.5–1.8 g ⋅ L^-1, glucose is approximately 1.5 g ⋅ L^-1, and urinary protein content is lower than during submaximal work.

The least intense exercises in the moderate power zone are performed at maximum aerobic energy production. Oxygen demand can reach 500–1500 L, while the oxygen debt does not exceed 5 L. Blood lactic acid content stands at 0.6–0.8 g ⋅ L^-1. Over the course of the work, it can be extracted by tissues and oxidized aerobically. Due to the intensive depletion of liver glycogen reserves, blood glucose levels drop below 0.8 g ⋅ L^-1. Protein breakdown products appear in the urine in substantial quantities, accompanied by significant loss of Water and mineral salts by the body.

In endurance training, aerobic energy supply processes play a major role; therefore, the primary exercises for their development are physical loads belonging to the high and moderate power zones with work intensities around W_AT and W_crit. The development of special speed endurance is supported by a high level of aerobic and glycolytic processes during work. This is achieved by incorporating exercises predominantly from the submaximal power zone into training, performed at an intensity level of W_exh. To enhance the motor qualities of maximum strength and speed, exercises from the maximum power zone with limit and near-limit intensity at the W_max level should be utilized, as they exert the greatest impact on developing the creatine phosphate Mechanism of ATP resynthesis.

In recent years, a more detailed classification of cyclic physical exercises has been developed. According to Ya. M. Kots (1986), physical exercises are divided into eight groups: three anaerobic and five aerobic.

Anaerobic exercises include: 1 — exercises of maximum anaerobic power (up to 15–20 s); 2 — near-maximum anaerobic power (up to 20–45 s); 3 — submaximal anaerobic power (up to 45–120 s).

Aerobic exercises include: 1 — exercises of maximum aerobic power (3–10 min); 2 — near-maximum aerobic power (10–30 min); 3 — submaximal aerobic power (30–80 min); 4 — moderate aerobic power (80–120 min); 5 — low aerobic power (over 2 hours).

Review Questions

1. What determines The Nature of the biochemical processes involved in energy supply during muscular activity?

2. What is The sequence of activation of the body's biochemical energy supply systems during work of varying intensity and duration?

3. What are the energy resources that sustain muscular work of varying intensity and duration?

4. How does the rate of ATP resynthesis in aerobic and anaerobic processes change depending on intracellular oxygen tension?

5. What is The Role of Hemoglobin and Myoglobin in supplying the body with oxygen?

6. What biochemical changes occur in The Heart muscle, Brain, working muscles, and blood during muscular activity?

7. What is the basis for classifying physical exercises by zones of relative intensity?

8. What are the characteristics of oxygen and energy supply to the body during exercise across various intensity zones?

9. What biochemical changes occur in the blood during physical exertion across various intensity zones?

10. How do biochemical METABOLISM/26.html">Energy Metabolism processes correlate with work capacity at the levels of W_ПАНО, W_крит, W_ист, W_ма?

11. Provide a biochemical profile of your chosen sport, taking into account the classification of physical exercises by zones of relative intensity.

12. Justify the necessity of using core training exercises in your chosen sport based on the dynamics of biochemical energy supply processes at various intensity levels (W_ПАНО, W_крит, W_ист, W_ма).