Dr.Biol., Professor J.V. Koryagina1
PhD G.N. Ter-Akopov1
PhD S.V. Nopin1
PhD L.G. Roguleva1
1North-Caucasian Federal Research and Clinical Center of the Federal Medical-Biological Agency, Yessentuki
Keywords: chronobiology, biological rhythm, desynchronosis, athletes, health, physical working capacity.
Introduction. The body adaptation to environmental conditions implies a wide range of functional capacities and fast change of the most important physiological systems to a new level of functioning . Biorhythm desynchronization and restructuring is due to certain stresses leading to unfavourable, sometimes pathological health deviations [2, 6]. In this regard, as well as for the purpose of the more accurate assessment of the functional state of the cardiovascular system of athletes training in extreme environmental conditions, scientists recommend measuring the biorhythms of the physiological parameters estimated.
The study was conducted as part of the government task given to FSBI NCFRCC FMBA of Russia to provide applied research work on the topic: "The benefits of chronobiological approach in practice of rehabilitation measures for athletes: search for the internal desynchronization markers and development of the methods of chrono-optimization of sports working capacity by means of BAS of plant origin (found in the Black Sea area)".
Objective of the study was to rate the circadian (circadian) biological rhythms in elite athletes in different competitive processes and special environmental (middle altitude) conditions.
Methods and structure of the study. The studies were carried out in the middle altitude conditions, upon the mountain Maloye Sedlo, Kislovodsk, Russia, at the altitude of 1240 m, during the training camps based at FSUE Yug-Sport. Subject to the study were 16-30 year-old athletes with different sports qualifications (MS, MSIC and HMS) engaged in different sports: weightlifting (n=12), boxing (n=14), shooting (n=20), wheelchair fencing (n=15), modern pentathlon (n=20). Their physiological parameters and circadian rhythms (CR) of the heart rate were measured.
When organizing the chronobiological study, the basic rules of planning and conducting observations were kept [4, 5]. HR measurements were carried out with the help of full-time monitoring using fitness trackers Polar M 200. The pulse data were taken to calculate the biorhythms registered by the fitness trackers. To process the chronobiological data, we used a Cosinor analysis, proposed by F. Halberg  and described by V.P. Carp and G.S. Katinas [4, 5]. The study of the athletes’ physiological parameters when observing the urgent effects of adaptation to the middle altitude conditions was carried out using the hardware and software complex ESTECK System Complex (LG Technology, USA). We analyzed the parameters of blood saturation, oxygen consumption, base rhythms of RR intervals of heart rate variability, temporal and spectral analysis of intervalogram, pulse wave analysis, hemodynamic parameters and arterial stiffness. Mathematical data processing was carried out using the computer programs Microsoft Excel 2016, Cosinor-Analysis 2.4 for Excel 2000 / XP  and Cosinor Ellipse 2006 .
When in the middle altitude conditions, it is the oxygen saturation indicators that are first to change; as such we studied the saturation indicators. According to the data obtained, saturation was below 97% for all athletes, which indicates the state of hypoxia. In terms of oxygen consumption at rest, the highest values were found in the athletes engaged in shooting sports and modern pentathlon, and the lowest - in the athletes with disabilities practicing wheelchair fencing.
All athletes were subject to morpho-functional analysis. The findings showed that the mean values of all the studied indicators were mostly within the physiological norm. In terms of the autonomic regulation of the heart rhythm, male boxers and women engaged in wheelchair fencing and modern pentathlon were found to have slightly higher values of the high frequency wave power, which indicates greater involvement of the parasympathetic nervous system in the heart rate regulation.
In the male weightlifters and male athletes doing wheelchair fencing the index of tension of regulatory systems was slightly higher as compared to other groups of athletes, which may indicate increased activity of the sympathetic nervous system and an increase in the degree of centralization of the heart rate control. All examined athletes demonstrated high values of the left ventricular function marker, which results from long-term adaptation to high physical loads in elite athletes.
During the chronobiological study, the heart rate was taken as the main physiological indicator. The group Cosinor analysis revealed statistically significant HR circadian rhythm values in all groups of athletes. In the male weightlifters, mesor was 76 bpm, the 24-hour rhythm acrophase - 16 hours, the amplitude - 9 bpm.
Results and discussion. The comparative analysis of CR in men and women involved in the same sport showed that the HR circadian rhythm parameters slightly differed. The group and individual CR parameters in the female shooters were as follows: mesor - 69 bpm, acrophase - 17 hours, amplitude - 9 bpm; versus 67 bpm, 17 hours and 8 bpm in the male shooters respectively.
In athletes with disabilities, engaged in wheelchair fencing, the CR parameters were slightly different from those in healthy athletes. In the women mesor was 74 bpm, rhythm acrophase - 15 hours, amplitude - 11 bpm versus 74 bpm, 15 hours and 14 bpm in the men respectively.
One of the functional laws being fundamental for human development states that "Any function performed intensively and for a long time weakens the organ". It is modern pentathlon that implies high-intensity and heavy loads. The study of the rhythmicity of heart rate in athletes engaged in modern pentathlon identified a pronounced HR circadian rhythm. In the women involved in pentathlon mesor was 74 bpm, rhythm acrophase - 15 hours, amplitude - 14 bpm. In the elite male athletes doing pentathlon, the HR circadian rhythm parameters were as follows: mesor - 71 bpm, rhythm acrophase - 17 hours, and amplitude - 17 bpm. In our opinion, the large amplitude values registered in the pentathlon athletes may be due to the fact that in the process of sports activity they have to solve more diverse tasks in terms of their nature, intensity and volume, and perform heavy loads.
According to the research data, in normal conditions, different physiological processes are characterized by different amplitudes and average levels, and in the state of tension the amplitude of rhythm oscillations increases . In this regard, the high CR amplitude of the athletes’ HR can be deemed as a result of tension of the adaptation processes during the period of simultaneous adaptation to hypoxia in mid-mountain conditions and high physical loads.
Evaluation of the hemodynamics and heart rate variability parameters in individual athletes when adapting to the middle altitude conditions revealed some deviations from the physiological norm. In this regard, these athletes were attributed to Experimental Groups (regardless of their sports specialization and gender) to identify specific features of circadian biorhythms in terms of adaptation to stresses, which, as known, can be the initial stage of various pathological processes . Four groups were formed: Group 1 - athletes with high systolic blood pressure (SBP) (SBP at rest - more than 130 mmHg), Group 2 - athletes with low SBP (SBP at rest - less than 110 mmHg), Group 3 - athletes with hypoxia - saturation values being less than 95%, Group 4 - athletes with high tension index (more than 150 c.u.).
The Cosinor analysis of the 24-hour harmonic of HR in the athletes with higher SBP rates also showed a significant HR circadian rhythm. Mesor was 72 bpm, the rhythm acrophase was 16 hours, the amplitude was 13 bpm. The analysis of the HR circadian rhythm in athletes with lower blood pressure rates showed a significant CR. The rhythm parameters differed significantly from those in the athletes with higher blood pressure rates by the lower mesor values and rhythm amplitude: mesor - 65 bpm, rhythm acrophase - 16 hours, amplitude - 9 bpm.
The analysis of the HR circadian rhythms in athletes with the lower blood pressure rates revealed a significant CR with mesor being 68 bpm, rhythm acrophase - 16 hours, amplitude w-as 11 bpm. The analysis of the HR circadian rhythms in athletes with highly tensed control mechanisms also revealed a significant CR with mesor being 75 bpm, rhythm acrophase - 15 hours and amplitude in this group of athletes being the highest and amounting to 15 bpm. These data once again confirm our hypothesis and opinions of other scientists about the increase in the CR amplitude in terms of tension of the adaptation processes.
Conclusion. The effectiveness of muscular activity is determined by the dynamics of the physiological functions of the human body during the day. At the same time, physical load itself has a significant effect on the rhythmicity of the body functions. Tension of the adaptation processes in athletes, detected by the deviations from the normal physiological indicators, does not cause any disorders in the physiological process rhythms in the middle altitude adaptation period, but is reflected in the circadian rhythms in the heart rate. Athletes with the lower blood pressure rates are tested with the lower mesors and amplitudes of the HR circadian rhythm; and those diagnosed with highly tensed control mechanisms are tested with the high rhythm amplitudes and mesors.
Rating the biological rhythms of the basic functional systems of the human body during their adaptation to muscular load and environmental conditions makes it possible to expand a contemporary view of the adaptation processes and identify the main directions and ways to enhance man’s reserve capabilities.
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Objective of the study was to rate the circadian (circadian) biological rhythms in elite athletes in different competitive processes and special environmental (middle altitude) conditions. The study data and analysis found expressed circadian rhythms in the heart rate of the elite athletes in the periods of the term hypoxic adaptation in the middle altitude environments under heavy physical workloads. Tense adaptation processes in the athletes rated by deviations of the physical working capacity rates from the norms were found to affect the rhythm amplitude and mesors without disorders in the physiological process rhythms in the middle altitude adaptation period. Athletes with the lower blood pressure rates are tested with the lower mesors and amplitudes of the HR circadian rhythm; and the athletes diagnosed with highly tensed control mechanisms are tested with the high rhythm amplitudes and mesors.