S.S. Grechishkina, Ph.D
Research institute of complex problems of Adygei state university, Maikop
M.N. Silant’ev, Ph.D
E.A. Ivantsov, postgraduate

Key words: heart rate variability, adaptive regulatory status, students, football.

Introduction. For some of students sport is a significant part of life being in some way an antistress factor [4]. Physical loads play an important role in forming the body’s adaptive reserves [14, 15, 17]. At the same time, competitive and training activities along with university educational load require high demands to functional abilities of the body that is especially typical for sport games. Any inconsistency between the amount and intensity of physical load and body adaptabilities can cause a number of changes in functional systems of the homeostatic level, change the body's regulatory-adaptive status, predetermining the present and further adaptation course [1, 11, 13, 16, 19].

The issues of the influence of physical loads on the functional status and body adaptabilities are usually considered without taking into account the state of regulatory mechanisms. The analysis of detected changes of physiological parameters doesn't provide the full characteristic of body adaptabilities, if another important parameter of its functional state - the quality of reserves control - is not determined. At the same time, heart rate, conditioned by the two main mechanisms of the regulation system - central and autonomous, is considered as a quite objective quality indicator of the control of reserve abilities of the body in general [2, 9, 12]. The transition from the urgent stage to the stable long-term adaptation influenced by sports physical loads is based on the formation of functional changes primarily in the cardiovascular system and its regulatory mechanisms [3, 8, 10, 18].

Students without any sports grade, engaged in sports sections, experience regulatory-adaptive reorganizations that have hardly been studied. That doesn't provide an effective solution for the issues of motor activity optimization for health protection and recovery of physical working capacity and prevents from carrying out preventive and corrective measures of psychoemotional overload during university studies.

The purpose of the study was to examine the influence of physical loadings of various orientations on the quality of regulation and adaptabilities of cardiovascular system of students doing sports in a sport section.

Materials and methods. The study was carried out at the "Child Development Physiology" laboratory of the Scientific research institute of Complex Problems of ASU with 2-4 year students of non-sports faculties doing football in sports sections. 25 football players at the age of 18-21 without sports grade and with sports experience of 3-4 years were examined (EG). Control group (CG) consisted of 35 practically healthy 2-4 year-students with the traditionally regulated motor mode (2 hours of physical education per week). HRV wave structure was studied using the "Poly-Spectrum-12" hardware-software complex by "Neurosoft" company (Ivanovo town) in the supine position for 5 minutes and in the active orthostatic test in the standing position for 6 minutes.

The time analysis indicators included: SDNN, reflecting the change of the autonomic and central regulation circuit, RMSSD - the autonomous regulation circuit activity, PNN50, indicating the relative predominance of the parasympathetic or sympathetic regulation units, measured in ms, and CV, characterizing the overall effect of the autonomic blood circulation regulation, measured in percentage.

Spectral analysis consisted of measuring the power of VLF, LF, HF (very slow, slow and fast waves, respectively) in the spectrum of heart rate variability and was implemented as a percentage of the spectrum total power (TP). The periodic sinus rate frequency changes were characterized on the basis of the HRV spectral analysis [2].

The study was carried during the preliminary period of the year training cycle, which was intended to form sports shape, to achieve the interrelation between physical, sports-technical, tactical and volitional skills. 60% of the preliminary period was dedicated to conditioning, 40% - special physical training.

Results and discussion. The use of statistical, time and spectral analyses of heart rate has revealed the economization of functions of the cardiovascular system (CVS) at rest in the majority of students, involved in football in sports sections. The most favourable balance at rest was observed when the fast HF-waves (32,3±7,5% against 27,7±5,2% of the students not involved in sports, р ≤ 0,05) prevailed in the heart rate regulation spectrum and their power is a marker of vagal effects on the heart. RMSSD indicator also testified to the increase of the tone of the parasympathetic nervous system (Tab. 1). The activity of parasympathetic autonomic nervous system with relatively low HR values (67,6±9,4 bpm in football players) according to R.M. Baevsky (2006) is an indicator of high adaptive potential of CVS. It is known that prolonged sports exercises lead to the structural and functional reorganizations of autonomic regulation [7, 10].

Table 1. HRV indices at rest in students involved in sport in sports sections (without sports grade) and not involved in sport, M±m

* – significance of differences (р≤0,05) between football players and non-athletes.

Almost all students not involved in sport had the increased HR control centralization, proved by the SDNN indicator decline, the predominance of slow LF-waves and the increased ratio of the sympathetic and parasympathetic regulation components (LF/HF) (Tab. 1). The literature considers the central regulation circuit activation as a stress phenomenon, reducing the adaptive-regulatory system lability under the influence of the educational and training loads. According to the adduced facts, one can assume on the heart rate regulation optimization in football players influenced by regular sports physical loads. Students not involved in sport didn't show such consistency between the central and autonomous regulation circuits.

The heart rate variability (HRV) analysis enabled to determine the typological features of the active autonomic heart rate regulation. So, all of the students regardless their motor mode had one of the three revealed types of adaptation: high level of adaptation (47,0% of football players), regulatory mechanisms tension (20,0% of football players and 48,0% of students not involved in sport), unsatisfactory adaptation (33,0% and 52,0% respectively). None of the students not involved in sport had the high level of adaptation.

The HRV analysis showed that football players with high level of adaptation had stable favourable balance at rest with the significant predominance of parasympathetic (HF) effects over the sympathetic (LF, p ≤ 0,05) associated with the activation of the suprasegmental regulation mechanisms (VLF-waves) of the heart rate (Fig).

Fig. HRV indices at rest and in conditions of AOT in football players with high level of adaptation of cardiovascular system (group 1), with tension of adaptive mechanisms (group 2) and unsatisfactory adaptation of cardiovascular system (group 3)

The time analysis also showed the predominance of the parasympathetic regulation link, that can be interpreted as the most optimal combination of the centralization and autonomy of the heart rate control [18].

The active orthostatic test (AOT) in this group of football players showed the preservation of the optimal level of autonomic regulation of the spectrum power. The spectral wave distribution fit into the pattern LF>VLF>HF in football players. That indicates the adequate activation of the sympathetic division due to the increase of LF-waves i.e. central-autonomous variant of regulation.

Football players with the adaptive-regulatory mechanisms tension had the total power (TP) of the spectrum decreased 1,6 times compared to the group 1, indicating the increased load on the regulatory mechanisms (Fig.1). It should be emphasized that compared to the students with high level of adaptation all the time analysis indicators were decreased. The LF-waves amplification indicates the subcortical centers activation, which means the adaptive-regulatory mechanisms tension. This is confirmed by the great contribution of VLF-waves. In the context of AOT there is a relatively slight activation of the sympathetic link of regulation compared to the state of rest with the significant increase in the cerebral ergotropic influence (VLF - 40,8 ± 4,5 against 29,3 ± 14,6%. P ≤ 0,05), indicating the reduction of the functional reserves of the adaptive-regulatory mechanisms of cardiac activity.

Football players with unsatisfactory adaptation of the regulatory systems were characterized by the increased centralization of heart rate mechanisms (Fig.1).  The low value of the pNN50 indicator relatively to the first and second types of adaptation is caused by the significant tension of regulatory systems, when supreme control levels are activated, which leads to almost complete suppression of the autonomous circuit activity. The total spectrum power is 3,3 and 2,0 times lower than in the first and second types of adaptation. Some authors consider this as a sign of decrease of the protective and recovery activity of the parasympathetic link of regulation [2, 5]. This concept is confirmed by the fact that football players with the third type of adaptation have the increased tonus of the sympathetic nervous system (LF-waves – 35,8±8,7%) like a universal mechanism of stress realization against the background of the low regulatory-adaptive status. The largest share of the HRV spectral components belonged to the VLF-waves indicating the significant influence of the suprasegmental mechanisms on the heart rate formation and reflecting the energy deficient state of athletes' body.

AOT of the football players with unsatisfactory adaptation revealed an increase of the sympathetic link of regulation with insufficient reactivity of the parasympathetic ANS. There was significant growth of LF-waves with a sharp decline of the contribution of HF-waves, whereas the contribution of VLF-waves in the total power was slightly decreasing. This is caused by the exhaustion of functional reserves of adaptive-regulatory mechanisms, as a result the regulatory systems cannot provide a favourable autonomic balance even at rest and in the necessity of urgent response to nonspecific stress the central circuit activation of cardiac activity is increased. At the same time the balance of sympathetic-vagal effects on heart rate (LF / HF - 2,2 ± 0,5) shifted to the predominance of the sympathetic nervous system influence. On this basis we can mark the state of overexertion and overtraining of the football players with unsatisfactory adaptation.

Students not involved in sports with the adaptive-regulatory mechanisms tension (48,0%) had the low values of spectrum power and contribution of the HF-waves (Table 2). The greatest contribution to the rate spectrum was made by the slow first-order waves (LF) and fast waves (HF), while the suprasegmental mechanisms activation (VLF) was expressed significantly, indicating the higher level of tension of the regulatory mechanisms amongst the all surveyed with different types of adaptation.

The AOT analysis of the students not involved in sports showed the strongly pronounced adaptive-regulatory mechanisms tension. Mobilization of functional resources is required to maintain the balance of cardiovascular system in this group. Sustainable level of adaptation is maintained only by the regulatory systems tension. Students not involved in sports with unsatisfactory adaptation (Table 2) in the HRV spectrum had the high values of VLF- and LF-waves against the background of significant decline of HF-waves. It can be considered as a phenomenon of a significant tension of the adaptive-regulatory mechanisms, when these students (52,0%) are in the state of tiredness. At the same time, the significant part of the LF/HF ratio (1,6±0,9) in the heart rate modulation, the low value of the HF-component, the SDNN decrease of the students not involved in sports allow to assume the inappropriate functioning of the inhibitory autonomic effects, which wasn't observed in the group of football players with the same type of adaptation.

Table 2. HRV indices in students not involved in sport at rest and in conditions of AOT at different types of adaptation: with tension of regulatory mechanisms and unsatisfactory adaptation of cardiovascular system, M±m

* on the right – reliability of differences (р≤0,05) between athletes within one group; * on the left – reliability of differences (р≤0,05) between athletes from different groups

The AOT results of the non-athlete-students with the unsatisfactory adaptation showed the sharp increase in functioning of the sympathetic part with the insufficient reactivity of the parasympathetic part. The total HRV became significantly low according to SDNN and TP. The balance of the sympatho-vagal effects on heart rate (LF/HF) shifted to the strong predominance of the sympathetic nervous system influence. There was significant growth of LF-waves with the sharp decrease of the HF-waves contribution (р≤0,05). It means that regulation systems cannot provide the favourable autonomic balance in the necessity of urgent response to nonspecific stress, resulting in the increased activation of the central regulation circuit of cardiac activity.

In general, proceeding from the studies most of the students involved in football in sports sections had highly efficient cardiovascular system indicators. The influence of regular muscle activity forms the functional system which provides the optimal adaptation to physical loads [6, 7, 15]. However there is a certain number of students with unsatisfactory adaptation of the cardiovascular system. It is necessary to solve the issue of individual adaptation in the conditions of mass sport to control the adaptive process effectively, to prevent the adverse functional shifts and preserve students’ health. Only the knowledge of the individual regulatory adaptabilities of the body during football classes will prevent the use in physical education of insufficient and excessive physical loads beyond the regulatory adaptabilities of the body, dangerous for the students’ health.

Conclusions.

1. The detected increase of the contribution of HF-waves to the general spectrum of heart rate variability at rest in students engaged in football indicates the improvement of regulatory adaptabilities, slackening of corticosubcortical effects on heart work and activation of self-regulatory processes, body’s energy-saving behavior.

2. Three types of adaptation were allocated by the indicators of heart rate variability and the tension level of regulatory mechanisms at rest: high level of adaptation (47,0% of football players), tension of regulatory mechanisms (20,0%) and insufficient adaptation (33,0%). The risk group is made of students not doing sports without the high level of regulatory-adaptive status, doing sports, among them there is no contingent with the high regulatory and adaptive status, with a high percentage of unsatisfactory adaptation (52.0%) and with the significant predominance of sympathetic component in the modulation of heart rate, indicating the inappropriate functioning of the inhibitory autonomic effects.

3. The differences in the adaptive regulatory status of representatives of various types of adaptation of cardiovascular system were presented in the study. High values of SDNN and RMSSD prevail over the low frequency LF-waves. Within the group with adaptive mechanisms tension in the total spectrum power the power of the high frequency HF-waves is decreasing with the increase of the very low frequency VLF-waves, indicating the increase of the sympathetic link of regulation and the decline of the functional reserves of heart rate regulation. Within the group with unsatisfactory adaptation the sympathetic link of regulation (LF) dominates significantly over the parasympathetic link (HF) and the SDNN and RMSSD values 2 times lower compared to high level of adaptation especially amongst the non-athlete students, indicating the strong tension of mechanisms of the cardiac activity regulation.

4. In case of the active orthostatic test in football players along with high level of adaptation the autonomic central variant of regulation is marked accompanied by coupled growth of the LF- and VLF-waves.  In AOT of football players with the regulatory mechanisms tension there is a central variant of the regulation against the background of suprasegmental adaptive mechanisms activation and the regulatory-adaptive status disruption. There is only the central variant of the heart rate regulation in AOT of the football players with unsatisfactory adaptation, indicating the orthostatic instability and the tension of regulatory-adaptive mechanisms.

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Author’s contacts: S4209691@yandex.ru