Professor, Dr.Biol. R.V. Tambovtseva
Russian State University of Physical Culture, Sport, Youth and Tourism (SCOLIPC), Moscow

Keywords: anaerobic glycolysis, lactic and pyruvic acid, oxidation processes, glycolysis, dynamic load.

Introduction. At present time, the problem of age-related development of metabolism and physical working capacity during the postnatal ontogenesis is still relevant and inexhaustible [1,3,4,5,7,8,9,10,12,14]. The ontogenesis of physical working capacity and energy supply of the muscular function is a heterochronic process of formation and interaction of different mechanisms underlying any physiological process [7]. The role of anaerobic glycolysis in the energy supply of muscular activity is determined by a number of endogenous and exogenous factors such as: age, sex, intensity and time of execution of exercises, fitness level, nutrition, the ratio of different types of muscle structures, etc. During the postnatal ontogenesis, the opportunities for functional exchange may be limited due to the heterochronic growth processes, muscle gains, changes in the composition of different types of muscle fibers and endocrine changes. The ratio of anaerobic and oxidation processes is usually expressed in the levels of blood lactic and pyruvic acids - substances in which the anaerobic breakdown of carbohydrates culminates and with which tissue oxidation starts. However, while an increase in the level of blood lactic acid indicates some predominance of anaerobic glycolysis over oxidation processes, it is difficult to explain an increase in the level of pyruvic acid during muscular activity. This is due to the fact that pyruvic acid is formed not only during the breakdown of carbohydrates, but also as an intermediate product of oxidation of glycerol, fatty acids and alanine deamination. According to literature data, the blood pyruvic acid level during muscular activity varies parallel to the level of lactic acid and is associated with active anaerobic processes [1,5,7]. In this view, it is highly important to determine the blood level of lactic and pyruvic acids during growth processes and under physical load.

Objective of the study was to determine the level of blood lactic and pyruvic acids depending on age and physical load.

Materials and methods. Subject to experiment were boys from 8 to 16 years of age (8 age groups) - Moscow school pupils. The studies were conducted in the same season. At the time of the study, the pupils were healthy and were allowed to participate in the experiment. In laboratory conditions, the 8-11-year-old subjects performed graduated exercises on a cycle ergometer (1.5 W/kg), the 11-20-year-old adolescents - 2.0 W/kg. The duration of the exercise was four minutes. Cadence was 60 rpm. The blood lactic and pyruvic acid levels were determined by the enzymatic method using the Dr. Lange photometric test kit and a standard Boehringer reagent kit.

The research results were statistically processed using the Statgraph software.

Results and discussion. As shown in Table 1, the levels of lactic and pyruvic acids do not change at the ages from 8 to 11 years.

Table 1. Dynamics in lactic and pyruvic acid levels at the age from 11 to 16 years depending on physical load.

By the age of 12 years, the concentration of lactic and pyruvic acids decreases significantly. At the age of 13 years, there is a sharp increase in the level of both blood lactic and pyruvic acids. By the age of 15-16 years, the level of the studied acids increases by 50% on the average compared with that in the 8-year-old boys.

Standard dynamic load of 1.5 W/kg, performed for four minutes, causes different metabolic reactions in boys of 8-10 years of age. At the ages of 8 and 9 years, the level of blood lactic acid remains increased 5 minutes after the load, compared with the initial value, by 26 and 19% respectively. We did not observe any increase in the lactic acid level in 10-year-old boys 5 minutes after the same load, while at the age of 11 there is another pronounced metabolic shift in the blood, which amounts to 48.3%. At the ages from 12 to 14 years, the reaction to standard physical load slows down gradually: 112.6; 84.9; 72.9%, and at the ages from15 to 16 years it accelerates again, running at 94.6%. A considerable increase in the blood level of pyruvic acid 5 minutes after the load was registered only in 12-year-olds.

Therefore, physical load of 1.5 and 2.0 W/kg, performed by 8-16-year-old boys for four minutes with cadence of 60 rpm, requires involvement of glycolytic mechanisms of ATP resynthesis. The role  of the anaerobic component in energy production during normal muscular activity depends on age and working capacity. Increased working capacity leads to intensification of glycolysis in the working muscles. The nature of reaction to loads of different intensity, as well as the role of anaerobic component in energy supply of normal muscular activity, indicate that at the age from 8 to 16 years the mechanisms of adaptation to physical load keep improving.

Age-related development of the aerobic source of energy production in skeletal muscles is not monotonous, and passes through a pronounced maximum at the prepubertal age. This has a major impact on the functioning of the entire system of energy supply of muscular activity. It can be assumed that in early childhood it is fatty acids that are the most important oxidation substrate both at rest and under physical load. After puberty, muscle glucose uptake, driven by glycogen resource utilization, starts prevailing in the substrate supply of mitochondrial oxidation during motor activity [7,10,12]. Increased muscle ability of primary school age children to consume oxygen manifests itself in a number of functional features, detected during muscular activity. Smaller oxygen debt in children indicates their lower anaerobic capacities and that muscle oxidative systems cope with the given load and therefore anaerobic sources are activated in the least [6,7]. If we study the physiological parameters contributing to this process, primary school age children are observed to have a more significant arteriovenous difference in oxygen tension during muscular activity [2,11], associated with the best conditions for diffusion, increased intensity of blood flow, greater activity of carbonic anhydrase and more powerful tissue oxidation systems [7]. The anaerobic-glycolytic source develops unevenly during ontogenesis, too. During puberty, anaerobic-glycolytic energy production suddenly activates, especially in boys [15]. The glycogen pool in the skeletal muscle grows significantly in the period between the second childhood (8-10 years old) and adolescence (17-20 years old). At the same time, the buffer capacity of blood increases. These age-related changes provide increased capacity of anaerobic glycolytic energy source, as it allows compensating for the resulting accumulation of lactate and the local oxidation. Regular changes in the metabolic component of energy processes in muscle tissues are due to the formation of definitive muscle fibers and improvement of the mechanisms of energy supply. Formation of definitive glycolytic muscle fibers first and foremost affects the anabolic steroid hormone - testosterone, which makes white muscle fibers grow significantly [7]. Using the biochemical, histochemical and physiological methods we found confirmation of the pronounced activation of the anaerobic-glycolytic energy production during pubertal changes, especially in boys [1,3,5,6,7]. Children and adolescents have a lower glycolytic capacity, but a higher aerobic capacity compared to adults, which helps them resynthesize ATP and creatine phosphate (CPh) during the recovery period faster [14]. In different age periods, metabolic supply of normal physical activity depends on the maturity of individual physiological systems and the functional abilities of the body. Knowledge of the physiological and biochemical characteristics, and adaptive capacities of the body of children and adolescents at various stages of development enables to regulate physical load so as to ensure the improvement of the functional systems and mechanisms of adaptation.

     Conclusion

• The gradual and heterochronic formation of the mechanisms of energy supply of muscular activity takes place at the age from 8 to 16 years.
• The role of the anaerobic component in energy production during normal muscular work depends on the age and working capacity.
• It is during puberty when the anaerobic component forms most intensively. Its formation is determined by the effects of anabolic steroids.

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Corresponding author: ritta7@mail.ru

Abstract.

Research objective was to investigate the dynamics of lactic and pyruvic acids in the ontogenesis in boys in the postnatal period. Pupils aged 8­16 years were involved in the experiment. They were offered load on a cycle ergometer. The lactic and pyruvic acid levels in the capillary blood were measured at rest and 5 minutes after exercise. It has been shown that the 1.5 and 2.0 W/kg physical exercise performed for 4 minutes requires involving glycolytic mechanisms of ATP resynthesis. The amount of anaerobic component in the power of standard muscular work depends on age and power. In the age range of 8­16 years, the degree of involvement of anaerobic glycolysis in power supply of standard muscular work is reduced, and an increase in its power leads to the intensification of glycolysis in the working muscles.