Dr.Biol., Professor A.A. Pseunok¹
PhD M.A. Mugotlev¹
PhD, Associate Professor M.N. Silantiev¹
R.A. Gasanova^2
1Adyghe State University, Maikop
²Kuban State Medical University, Krasnodar

Keywords: adaptation, heart rate, mechanisms of regulation, physical activity, functional reserves, young athletes, health protection.

Background. Heart rate regulation is still the problem at the forefront of modern physiology. As the practice of modern sports shows, nowadays, the functional reserves of the body are almost exhausted in terms of most of components, so are the possibilities for further increasing the volume and intensity of physical loads without risking athletes’ health. In this regard, the study of the heart rate variability in the 14-16-year-olds is of great interest.
The research data are particularly relevant for the developing body or beginner athletes, as knowledge of the processes of adaptation to regular muscle work is a prerequisite for both rational organization of the athletic training process and maintenance of the functional state of the body. Physiological indicators reflecting the functionality of the mechanisms of autonomic regulation of cardiac activity can be used as reliable body functional state and physical fitness rating markers [2, 4, 7-10].
Given the obvious relevance of the problem presented, we studied the integrated parameters of the cardiovascular system in the 14-16 year-old football players.
Objective of the study was to analyze the peculiarities of heart rate variability-based adaptation of young athletes to training loads.
Methods and structure of the study. The study involved the 14-16 year-old football players and was carried out in those periods of the academic year that were the farthest from the holidays.
Our aim was to obtain data at the time when the academic and physical loads had the greatest impact on the schoolchildren’s body.
By the end of the experiment, the respondents had 6 years of sports experience. The Experimental Group football players were trained under the program approved for the Children and Youth Sports School. The Control Group ones attended physical education classes - 2 hours a week.
The state of the cardiovascular system was rated by the R.M. Bayevsky Heart Rate Variability Test method (1985) [1].
A correlation analysis between the studied parameters was carried out.
The data obtained were processed by the method of variation statistics with the calculation of the arithmetic mean (M), arithmetic mean error (m), significance of differences (t) by the Student t-criterion,  and probability level (p).
Results and discussion. The study revealed a significant increase in the somatometric parameters of the 14-16-year-olds of both groups in two years. At the beginning of the school year, there were no reliable differences between the Experimental and Control Groups in terms of heart rate. In the 14-16 year-old schoolchildren of the Control Group, the average heart rate values were almost stable for two years, while in the young athletes the heart rate values decreased by the end of the second school year. The observed dynamics in the young athletes were deemed as good physical training level and earlier development of the parasympathetic division of the autonomic nervous system.
The Control Group boys were found to have changes in the variation range (ΔX), humoral regulation channel (Mo), and the central contour of autonomic regulation, which indicated that the physical load was consistent with their adaptive capabilities. But at the same time, as evidenced by the tension index values, at the beginning of the second year of studies, the number of sympathicotonics was one quarter of all surveyed and by the end of the school year decreased to 11%.
The variation range in the young football players during the second year of studies indicated the intensity of the adaptation mechanisms.
The average mode amplitudes indicated poor adaptation of the junior football players, although during the second year of studies, there was an upward trend in the percentage of schoolchildren with normal mode amplitudes and a downward trend in those with tensed adaptation mechanisms [3].
A new level of adaptive capabilities is formed as a result of long-term and targeted trainings.
As the fitness level increases, the autonomous contour of regulation starts to prevail, the heart rate regulatory mechanisms become decentralized, and the tone of the sympathetic nervous system is weakened, while the central mechanisms of heart rate regulation are strengthened due to overtraining [5].
Based on the teachings of H. Selye, the "cost of adaptation" should not exceed the functional resources of the body, which may result in a failure of adaptation with the development of pathologies. It is generally admitted that it is a state of overtraining in sports [6].
A correlation analysis between the between somatometric and heart rate variability parameters was conducted.
Small number of internal relationships were detected in the 14-16 year-olds who combined learning and sports activities, and no inter-systemic correlation relationships were identified between the anthropometric indicators and heart rate parameters. The detected correlation relationships indicated the formation of regulatory mechanisms (autonomic and central contours of regulation), while the absence of inter-system correlations testified to the "functional imbalance" of the body and heterochrony of physical development. We assume that unstable correlation relationships are due to the immaturity of the regulatory mechanisms. However, the breakdown of the old ties and the formation of new ones are indicative of the active evolution of adaptation responses.
As noted in the study, sports activities lead to a significant shift in both morphological and functional parameters of the cardiovascular system.
A good functional state of the athlete’s heart is seen as a long-term adaptive response, allowing for physical work that used to be impossible due to its high intensity.
Results and conclusion. The results obtained show that the resting heart rate structure changes under the influence of the extended motor mode, thus reflecting the processes of formation of new, more favorable relations: a decrease in the sympathetic and an increase in the parasympathetic influences on the heart. We also detected a stable reaction of the body of junior football players to increased motor activity, which was interpreted as an adaptive response. It is the autonomous regulation circuit that starts to prevail with increasing physical fitness level; the heart rate regulation mechanisms become decentralized and the tone of the sympathetic nervous system decreases, while the central mechanisms of heart rate regulation increase due to overtraining.
The data obtained can be effectively used in sports selection, training process management, prediction of overtraining and overstrain.

References

1. Bayevsky R.M., Kirillov O.I., Kletskin S.Z. Mathematical analysis of changes in heart rate under stress. Moscow: Nauka publ., 1984, 221 p.
2. Gavrilova E.A. Autonomic regulation of heart rate as criterion of pharmacological real correction athletes in sports. Heart rate and type of autonomic regulation in people's health and athletes' physical fitness assessment. Proc. VI nat. symp.. Izhevsk: USU publ., 2016. pp. 96¬-102.
3. Mugotlev M.A. Relationship of physical development and heart rate variability in 10¬17 year¬ old school students practicing football. PhD diss. abstr.. Maikop. 2007.21 p.
4. Pseunok A.A., Mugotlev M.A., Silantyev M.N. Mechanisms of the heart function control of young sportsmen aged 10¬14 (scopus). Indian journal of Science and Technology, Vol 8 (30), November 2015. DOI: 10.17485/ijst/2015/v8i30/85345
5. Rusanov V.B. Typological characteristics of autonomic regulation of heart rate of adolescents under various motor activity. Vestnik ChGPU, 2011. no. 6. pp. 313¬324.
6. Selye G. Essays on the adaptation syndrome. M.: Medgiz publ, 1960.254 p.
7. Seregina S.S. Monitoring of human adaptive capabilities. Ecological and physiological problems of adaptation: proc. X Intern. symposium. M .: PFUR publ, 2001. pp. 480¬-481.
8. Malik M. Heart rate variability. Curr. Opin. Cardiol.1998. N 13(1). pp. 36¬-44.
9. Nakanichi T., Yoshimura M. Elecent progress in Holter electrocardiography, focused on heart rate variability.  Rinsho. Byori. 1993. Vol. 41 (11). pp. 6¬13.
10. Sega S., Jager R., Kiauta T.A. A comparison of cardiovascular reflex tests and spectral analysis of heart rate variability in healthy subjects . C1in. Auton. Res. 1993.  Vol. 3(3). pp. 75¬-82.

Corresponding author: pseunokk@mail.ru

Abstract
Objective of the study was to analyze the peculiarities of heart rate variability-based adaptation of young athletes to training loads.
Methods and structure of the study. The study involved the 14-16 year-old football players and was carried out in those periods of the academic year that were the farthest from the holidays. By the end of the experiment, the sports experience of the respondents was 6 years. The RG athletes were trained in the traditional motor mode (two physical education lessons a week).
Results and discussion. The results obtained show that under the influence of the extended motor mode the resting heart rate structure changes, thus reflecting the processes of formation of new, more favorable relations: a decrease in the sympathetic and an increase in the parasympathetic influences on the heart. We also detected a stable reaction of the body of young football players to increased motor activity, which was interpreted as an adaptive response. With increasing physical fitness level, it is the autonomous regulation circuit that starts to prevail; the heart rate regulation mechanisms become decentralized and the tone of the sympathetic nervous system decreases, while the central mechanisms of heart rate regulation increases due to overtraining.
Conclusion. The data obtained can be effectively used in sports selection, training process management, prediction of overtraining and overstrain.