Associate Professor, Ph.D. V.V. Apokin¹
Associate Professor, Ph.D. A.A. Povzun¹
Professor, Dr.Hab. V.D. Povzun¹
Associate Professor, Ph.D. O.A. Fyntyne^1
1Surgut State University, Surgut

Keywords: schoolchildren, physical loads and emotional stress, functional reserves, adaptive capabilities, development of desynchronosis.

Introduction. Today, one of the main factors of control of the adaptation process is the possibility of an objective and accessible monitoring and prediction of the functional state of athletes and this problem becomes particularly important in the case of junior athletes [15]. Violations of the direction and content of the process of physical education of children during postnatal ontogenesis bear the risk of deterioration of physical and mental condition of a child, adaptive capabilities reduction, which further adversely affects his health and development [5, 6]. Ignoring age characteristics of the body leads to the excessive "physiological cost" of sports success on the background of intense growth processes and learning hard: the functional reserves of the body are being reduced, problems with health arise and slow down the growth of performance and consequently the motivation to sports is reduced [8, 9]. The health effect of mass youth sport is being lost, its role in the formation of a healthy and harmonious individual is being reduced, which inevitably affects the sphere of elite sport [6, 7]. The need to monitor the state of the functional and, above all, adaptive capabilities of the body of athletes can hardly be overestimated in this case [5, 9, 10].

Taking into account the principles of the interaction of the human organism with the environment is, in our opinion, one of the tools that can solve these problems [12-14, 16]. Biological rhythms are, on the one hand, one of the major mechanisms of adaptation to the environment, and on the other hand are seen as a universal criterion of the adaptive state of the body [18].

Purpose of the research. In view of the above the issue of individual organization of biological, especially circadian, rhythms of schoolchildren actively engaged in sports is of particular interest [18]. Such studies are of special importance with adolescents, as a growing body is most sensitive to damaging effects and primarily responds by changes in homeokinesis [9, 17].

Materials and methods. In order to assess changes in adaptive capabilities of the body taking place due to regular physical exercises, seasonal changes in circadian rhythms of the major physiological parameters in a group of healthy pupils aged 13­14 years, living in Surgut and actively engaged in sports, were compared. Logic and measuring technique are described in detail in work [9]. The data obtained were subjected to standard mathematical processing using FARS software application [3]. Daily average (diurnal mean value of a parameter), rhythm amplitude, the time of the highest value of a function (acrophase) and the amplitude of fluctuation (standard time-card of a parameter) were assessed.

Results and discussion. The analysis showed that the most significant changes in the rhythm structure occur in the cardiovascular system, the advantages of which as a system responsible for the adaptation of the body to a large number of various factors are known [4, 6], and it is the response of the circulatory system that provides the most illustrative and typical examples in mobilizing operational and strategic reserves, at the stages of urgent and long-term adaptation [1, 11]. Misaligned changes of the daily average values and the range of fluctuations, a significant reduction of the amplitudes of almost all indicators, multidirectional shift of acrophases indicate a severe strain in the functioning of the cardiovascular system, a decrease, especially towards spring time, of its functional reserves and adaptive capabilities and development of internal desynchronosis. First of all we should note that despite some increase of most diurnal mean values, especially in spring, there is a significant decrease in the amplitudes of all the indicators and specifically in cardiac output (CO) and minute blood volume (MBV) that characterize the functioning of the entire circulatory system. Evidence suggests that it is at this time that the functionality of the cardiovascular system is very small and it hardly copes with the stress. In addition, there are significant seasonal changes within it. Changes of daily average values are of the rhythmic but uncoordinated nature: indicators characterizing myocardial contractile function (HR, CO, MBV) slightly decrease in winter, and the ones characterizing blood pressure increase. Growth rates of blood pressure indicators practically stabilize by spring time, and there is a tendency of restoring the original values of HR, CO and MBV. 

The considerable decline in average daily HR values in winter is probably the reason for the mentioned changes, since it inevitably entails a reduction in MBV values too, and that along with intense exercise leads to serious stress of the circulatory system and the need to compensate for this reduction. Reduced heart rate cannot but has an impact on the blood pressure values. However, changes in average daily values and blood pressure range indicate an intensification of regulatory influences that not only compensate for the risk of blood pressure drop but can also affect the intensity of heart contractions. This compensates for the reduction in the average daily MBV indicator by spring time to a certain extent, but leads to a considerable desynchronization of HR and CO rhythms. It can be argued with high probability that such characteristics of changes of hemodynamics of circadian rhythms are response to physical load, since in a similar study conducted with the students of the Department of Physical Education of Surgut State University as subjects no similar changes were identified [10].

Consideration of changes of indicators characterizing the state of the other vegetative functions requires the same amount of attention. A progressive decrease in the amplitude and the range of the breathing rate that become quite significant by spring should be noted as the warning signs. Such a critical decline in adaptive capabilities of the system of external respiration requires careful consideration while organizing the training process in this period. In addition to reduced amplitude of the breathing rate (BR) in spring a discrepancy of phases (desynchronosis) of the breathing rate rhythm and lung capacity is observed, which is not only noted both in autumn and winter, but also significantly increases in spring.    

It is unlikely that such a situation can be accounted for by the influence of climatic factors only, regular physical loads can be a major cause [7]. If the shift of the lung capacity acrophase to morning is most likely the result of fitness, the shift of the BR maximum to a later part of the day (along with a significant reduction of its amplitude) indicates the development of significant internal stress in the system of external respiration.

Maintaining the seasonal lung capacity rhythm shows that a process compensating if not a temporary misalignment with breathing rate, then a misalignment with the reduction of its amplitude is likely to participate in ensuring the functionality of external respiration. However, additional research with a more detailed assessment of external respiration indicators is necessary to find the mechanism of compensation.

Thus, the observed seasonal decrease in the amplitudes of body temperature, breathing rate and almost all the studied parameters of the cardiovascular system shows a significant decrease in the adaptive capabilities of the body in winter and especially in spring time. It can be assumed that it largely is the result of a long-term (winter) impact of adverse climatic and environmental factors as acrophases of individual minutes, body temperature, hand strength, external respiration indicators hardly change seasonally, and thus time organization of these rhythms is maintained.  

Some increase of diurnal mean values, and especially the amplitudes of hand strength indicators observed throughout the studied period can be attributed not so much to the change of rhythm but rather to the increase of physical fitness level as a result of continuous and intense workouts. In addition, it should be taken into account that the young men of the studied group are in a period of active growth and puberty, which inevitably affects the physical development indicators. The change of lung capacity characteristics probably takes place for the same reasons. 

Seasonal increase of the amplitude of individual minute indicator while there is a reduction in its average daily value as well as the acrophase shift to a later time indicate permanent fatigue development, especially in the central nervous system that is most likely due to the intensity of the learning process.  Since physical performance indicators improve, it is unlikely that the fatigue is associated with physical loads; however, this characteristic of the reaction to the load should be especially taken into account, since the internal count of periods of time plays a specific role in physiological processes and underlies the sense of time punctuality required for success and effectiveness of most activities requiring various manifestations of rational and emotional nature. Behavior of this kind is most pronounced in sports [2]. Internal time-keeping property largely determines the readiness of an athlete to the load and his ability to reach the set target with the highest result without compromising his health, as it is one of the most important factors of human adaptation to changing environmental conditions.  

Conclusion. In view of the above a detailed and comprehensive study of consistent patters and conditions of the interaction of various factors contributing to the cyclic macrostructure of the process of individual sports perfection deserves close attention. The prospects of optimization of long-term sports activity, appropriate adjustment of its dynamics, and increase of its efficiency largely depend on the deployment of such studies, so any research in this direction is, of course, important and promising, has some fundamental and practical significance, which has predetermined our choice of this direction of scientific research.

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Corresponding author: apokin_vv@mail.ru