Dr.Med., Professor A.L. Korepanov
Sevastopol State University, Sevastopol

Keywords: adolescents, juniors, physical development, heart rate variability.

Introduction. The most important challenge of modern sports science, which is based on the age-specific human motor skills evolution concept and anthropic educational technologies [9], is to study the functional resources of the body of adolescents and juniors in order to improve the athletic training process and prevent diseases. The cardiovascular system of junior athletes is vulnerable when exposed to heavy sport-specific loads, which can lead to pathological changes in the heart and blood vessels [2, 12]. In recent years, there has been a decrease in the level of children's health and an increase in the number of cases of pediatric cardiac pathologies [4, 6]. The number of adolescents with high blood pressure is increasing, 50% of students demonstrate an unfavorable type of reaction to dosed physical loads [5]. The study of the hemodynamic characteristics of adolescents showed that the cardiac contractile force depends on the pace of physical development and its rates are lower in children with high growth rates [8]. It also found reduced blood circulation efficiency, decreased adaptation potential, and tension of the cardiovascular system of students [3]. Negative dynamics was detected in the students’ cardiac functionality and contractility rates during their university studies [7]. 
An effective way to assess the heart condition is to conduct a heart rate variability (HRV) analysis enabling to determine the nature and degree of tension of regulatory mechanisms, the ratio of the tones of the sympathetic and parasympathetic divisions of the autonomous nervous system (ANS), the effects of the autonomic and central contours of autonomic regulation [1]. It is shown that the HRV analysis made it possible to assess the dynamics of adaptation processes and the risk of cardiac abnormalities in terms of muscle activity [10], as well as optimize the system of training of highly qualified athletes [11]. The above determines the significance of studies of the vegetative status of adolescents and juniors based on their HRV rates for substantiating and developing methods to prevent cardiac pathologies during the training process.
Objective of the study was to obtain and analyze the heart rate variability test data of the Sevastopol adolescent and junior male population.
Method and structure of the study. Sampled for the study were 82 residents of the city split up into the 13-14 year old (n=26), 17-18 year old first-year student (n=29) and 21-22 year old fifth-year student (n=27) groups. The research was carried out in the Sevastopol State University Laboratory of Physiology. The ECG and HRV analyses were carried out by means of variation pulsometry using MTK-30 Cardiac Function Analyzer (city of Krasnodar). ECG was recorded in the standard lead II in a quiescent state for 2 minutes, in the supine position after a 5-minute rest break. The following indicators were registered: mode (Mo) - the most common cardio-interval value in the given time series, which characterizes the overall level of functioning of the sinus node and the share of hormonal regulation; mode amplitude (AMo) - the number of mode values as a percent of the total number of cardio intervals, reflecting the level of activity of the sympathetic division of ANS and the share of the central contour of autonomic regulation; variation range (ΔX) - the difference between the maximum and minimum values of RR intervals, reflecting the level of activity of the parasympathetic division of ANS; standard deviation (SD) - the standard deviation of normal RR intervals, which is an integral indicator of HRV, characterizes the vegetative balance and is analogous to SDNN proposed by the European Society of Cardiology and the North American Society of Pacing and Electrophysiology [1, 13]. Bayevsky’s tension index (TI) was calculated by the formula as follows:
TI = AMo/(2×Mo×∆X),
where, TI is an integral indicator of the functional state of regulatory systems, reflecting the bodily adaptation resources and the degree of centralization of hart rate control. The initial vegetative tonus was determined as balanced at TI ranging between 30-90 c.u.; as vagotonia - at TI below 30 c.u.; as sympathicotonia - at TI ranging between 90-160 c.u.; as hypersympathicotonia - at TI above 160 c.u.
The data were statistically processed using the software package STATISTICA for WINDOWS 6.0.
Results and discussion. It was found that the adolescent and junior boys had different levels of functioning of the autonomous nervous system (Table 1).

Table 1. HRV test data (Мm) in adolescent boys and junior male students

Note. [1] – р<0.05 as compared to the indices in the adolescents;  [2] – р<0.05 as compared to the indices in the 1st-year students.

As seen from Table 1, the temporal indices of HRV were higher in the adolescent male population than in the junior one. Thus, the variation range and standard deviation rates, the increase in which reflects the growing parasympathetic influences and expansion of the adaptive corridor of HRV, were found to be significantly higher (p<0.05) in the adolescent boys than in the 1st- or 5th-year male students. During the university studies, the parasympathetic influences on the heart rate decreased, which was confirmed by a significant (p<0.05) decrease in the standard deviation rate in the 5th-year male students as opposed to the 1st-year ones. In terms of ΔX, the differences between the 1st- and 5th-year male students turned out to be insignificant. The university students were found to have an increase in the sympathetic activity of the autonomous nervous system and centralization in the regulation of heart rate in terms of AMo: it was statistically significantly (p<0.05) higher in the students than adolescents. The analysis of the autonomic regulation of heart rate in terms of TI showed a different initial vegetative tonus in the studied groups. The regulatory systems were tenser in the junior male population (students): their TI was significantly (p<0.05) higher than in the adolescents. There were no statistically significant differences in TI between the 1st- and 5th-year students.
The study of initial vegetative tonus revealed significant differences in the sympathetic-parasympathetic balance in the adolescent and junior boys (Table 2).

Table 2. Structure of initial vegetative tonus in the adolescent and junior male population (% of total number of examined subjects)

It was shown that with aging, the share of the sympathetic unit of autonomous regulation increases: among the students, 55.5% of respondents were found to have an increased tone of the sympathetic division (sympathicotonia and hypersympathicotonia), whereas among the adolescents there were 38.5% of such individuals. There was a statistically significant – 3-fold – increase in the hypersympathicotonic conditions in the 1st- and 5th-year students (24.1 and 25.9%, respectively) as opposed to the adolescents (7.7%). The number of vagotonics reduced from 15.4% in the group of adolescents to 6.9% and 7.4% in the groups of the 1st- and 5th-year students, respectively. The number of individuals with the balanced vegetative tonus also decreased with aging: 46.7% - among the adolescents, 41.3% - among the 1st- and 33.3% - among the 5th-year stuents. From the 1st to the 5th year of university study, the number of eutonics decreased by 8% and that of sympathicotonics increased by 6%. The vagotonic and eutonic initial vegetative tonus was detected in 62.1% of adolescents, 48.2% of the 1st-year students and 40.7% of the 5th-year ones.
Conclusion. The analysis of the HRV rates revealed the increase in the tone of the sympathetic nervous system, increase in the role of the central contour of autonomic regulation and the decrease in the parasympathetic tone in the male students as opposed to the adolescent males, which was confirmed by a significant decrease in ΔX, SD and increase in AMo in the male students. Such sympathetic-parasympathetic balance was due to the tension of the regulatory systems: the juniors were found to have a higher TI, and among them there were a smaller number of individuals with the balanced vegetative tonus as opposed to the adolescents. During the university studies, there was a decrease in the HRV rates and a shift in the sympathetic-parasympathetic balance towards the sympathetic domain, as shown by the increase in the SD rate, decrease in the number of people with the balanced vegetative tonus and the increase in the number of sympathicotonics among the 5th-year students as opposed to the 1st-year ones. The results obtained indicate tension of the adaptive mechanisms of the students, caused by the information overload, hypodynamia, nutritional disorders, and bad habits.
The obtained data on the dynamics of HRV rates, vegetative tonus and tension index of the regulatory systems in the Sevastopol adolescent and junior male population will be applied to improve the training systems and prevent the pathological cardiac transformation in the age groups.

References

1. Bayevskiy R.M.. Berseneva A.P. Otsenka adaptatsionnykh vozmozhnostey organizma i riska razvitiya zabolevaniy [Assessment of bodily adaptive capability and risk of development of diseases]. Moscow: Meditsina publ.. 1997. 253 p.
2. Balykova L.A.. et al. Izmeneniya serdechno-sosudistoy i immunnoy sistem u yunykh sportsmenov: polozhitelnye effekty L-karnitina [Changes in cardiovascular and immune systems in junior athletes: positive effects of L-carnitine]. Pediatriya. App. «Consilium Vedicum». 2014. no. 4. pp. 20-24.
3. Voronina I.Yu. Sostoyanie serdechno-sosudistoy sistemy u studentov professionalnogo litseya vo vremya proizvodstvennoy praktiki [State of cardiovascular system in professional lyceum students during job practice]. Biologicheskie nauki. 2016. no. 45 (3). pp. 8-10.
4. Dolgikh V.V.. Prokhorova Zh.V.. Fomina N.A. Rol psikhoemotsionalnykh i sotsialnykh faktorov v razvitii essentsialnoy arterialnoy gipertenzii u podrostkov [The role of psycho-emotional and social factors in development of essential arterial hypertension in adolescents]. Pediatriya. 2011. no. 5. pp. 25-28.
5. Katashinskaya L.I. Funktsionalnoe sostoyanie serdechno-sosudistoy sistemy shkolnikov i studentov g. Ishima [Functional state of cardiovascular system of schoolchildren and students from Ishim]. Vestnik Tyumenskogo gosudarstvennogo universiteta. Sotsialno-ekonomicheskie i pravovye issledovaniya. 2009. no. 3. pp. 175-181.
6. Korepanov A.L.. Tumko V.V. Issledovanie urovnya zdorovya i psihomotornykh pokazateley u podrostkov [Study of health level and psychomotor performance in adolescents]. Gumanitarno-pedagogicheskoe obrazovanie. 2017. v. 4. no. 4. pp. 35-40.
7. Korepanov A.L.. Golovko O.N.. Vasilenko I.Yu.. Motornaya S.E. Funktsionalnye pokazateli deyatelnosti serdtsa u malchikov-podrostkov i yunoshey g. Sevastopolya [Functional indices of cardiac performance in adolescent males and young men in Sevastopol]. Teoriya i praktika fiz. kultury. 2016. no. 7. pp. 53-55.
8. Korepanov A.L. Funktsionalnye pokazateli deyatelnosti serdtsa u podrostkov s raznyimi tempami fizicheskogo razvitiya [Functional indices of cardiac performance in adolescents with different rates of physical development]. Teoriya i praktika fiz. kultury. 2016. no. 12. pp. 49-51.
9. Lubysheva L.I.. Zagrevskaya A.I. Kineziologicheskiy podkhod kak metodologiya sovremennoy sportivnoy nauki i praktiki [Kinesiological approach as methodology of modern sport science and practice]. Teoriya i praktika fizicheskoy kultury. 2015. no. 12. pp. 3-5.
10. Maltseva A.B.. Davydov P. V.. Lobov A.N. Ispolzovanie kardiointervalografii u vyisokokvalifitsirovannyih sportsmenov na primere sbornykh komand Rossii po legkoy atletike i biatlonu [Cardiointervalography in highly skilled athletes: case study of Russian national athletics and biathlon teams]. Lechebnaya fizkultura i sportivnaya meditsina.2009.no. 1. pp. 17-22.
11. Mikhaylov V.M.. Kharlamova N.V.. Belikova M.E. Variabelnost ritma serdtsa kak metod kolichestvennoy otsenki funktsionalnogo sostoyaniya sportsmenov [Heart rate variability as athletes' functional status rating method]. Meditsina i sport. 2005. no.1. pp. 19-21.
12. Basavarajaiah S. et al. Physiological left ventricular hypertrophy or hypertrophic cardiomyopathy in an elite adolescent athlete: role of detraining in resolving the clinical dilemma. Br. J. Sports Med. 2006. no. 40. pp.727–729.
13.  Heart Rate Variability. Standards of measurement. physiological interpretation and clinical use. Circulation. 1996. Vol.93. pp.1043 – 1065.

Corresponding author: akorepanov2006@rambler.ru

Abstract
Objective of the study was to obtain and analyze the heart rate variability test data of the Sevastopol adolescent and junior male population. Sampled for the study were 82 residents of the city split up into the 13-14 year old (n=26), 17-18 year old first-year student (n=29) and 21-22 year old fifth-year student (n=27) groups. The heart rate variability was tested by MTK-30 Cardiac Function Analyzer. The tests showed the student groups being more exposed (versus the adolescent groups) to pressures on the heart rate control systems with the growing tonus of the sympathetic parts of the autonomous nervous system and growing role of the central heart rate control system. The heart rate variability was tested to fall with the university age growth, with the sympathetic-parasympathetic balance shifted towards the sympathetic domain. The heart rate variability logics found by the study fairly well reflects the heart rate control systems functionalities and may be efficiently applied to improve the young people’s training and hearth pathology prevention systems. The analyses of the heart rate variability test data of the Sevastopol adolescent and junior male population will be applied to improve the training systems and prevent heart pathologies in the age groups.