Dr.Med., Professor O.S. Glazachev¹
Dr.Med., Professor V. Kofler¹
PhD, Associate Professor E.N. Dudnik¹
PhD A.I. Filipchenko^1
1I.M. Sechenov First Moscow State Medical University (Sechenov University), Moscow

Key words: hyperthermia, performance, endurance.

Introduction. Thermal acclimatization (TA) as a method of increasing the load endurance of athletes is widely used for training athletes of different sports [1, 3]. The results of these studies are quite contradictory and difficult to interpret, because they used different methods of TA, usually with the simultaneous use of training loads and additional stressors, which does not allow to assess the "contribution" of each of them in the subsequent increase in efficiency.
The aim of the study was to assess the effect of adaptation to passive hyperthermia on cardiorespiratory endurance and aerobic performance in Amateur athletes under increasing intensity load in thermo – neutral conditions.
Methodology and organization of the study. The randomized controlled study involved 28 Amateur athletes (M., Ms. age-20.2±2.1 years, sports-football, handball, sports experience-4-7 years). The research Protocol is formed in accordance with the provisions of the "Bioethical rules of human research" and approved by the bioethical Commission of the University. Athletes of the experimental group (14 people) underwent 24 procedures of passive hyperthermia – PG (used capsule "alpha basic" – Sybaritic Inc., Minnesota, USA. The average temperature in the capsule-65-80 oC. The duration of one procedure-40 minutes); control group participants (14 people) passed 24 interval training (it) on an elliptical simulator (moderate intensity load (45-55% of the individual heart rate max.). Athletes of the two groups did not differ in basic demographic and physiometric characteristics. Initially, after 12 and 24 PG/it procedures, all participants underwent a stress cardiopulmonary treadmill test according to the BRUCE Protocol. Before the start of the exercise test, respiratory function was assessed. Data analysis was performed using Statistica 11.0 software.
The results of the study and their discussion. It was revealed that the course of PG leads to a significant increase in aerobic performance, peak oxygen consumption (VO2 peak), oxygen consumption at the level of the anaerobic threshold (VO2 AT), increased cardiac performance. Since there were no significant changes in the analyzed indicators in the CG, we believe that the leading factor of the identified adaptive shifts is the action of hyperthermal stress. The noted effect of adaptation to hyperthermia can be partially explained by a number of morphofunctional shifts: improved cardiac performance due to a moderate decrease in blood pressure and postload, increased skin and muscle blood flow, blood plasma volume, decreased submaximal heart rate, stimulation of oxygen extraction by muscles by reducing the affinity of hemoglobin to oxygen, as well as stimulation of capillarization, increased power of antioxidant mechanisms, stimulation of nitrogen monoxide production as a modulator of oxygen-dependent processes, occurring in the body [1, 2]. It should also be noted a significant increase in pulmonary load ventilation and indicators of bronchial patency at rest (FEV1, PEF, MEF75–25), which can be considered a mechanism of adaptation to hyperthermia, positive in terms of optimizing load endurance, and not a decrease in load efficiency and an increase in the "ventilation" cost of performing the load [3].
Conclusion. The course of passive temperature acclimatization procedures leads to an increase in aerobic performance of Amateur athletes tested in conditions of temperature comfort. More research is needed to translate the effects on qualified athletes.
The work was partially supported by RFBR grant No. 19-013-00465 A "Direct and cross-effects of adaptation to systemic hyperthermia: impact on quality of life, neurohormonal and psychophysiological status of a person".

References

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2. Mero A., Tornberg J., Mäntykoski M., Puurtinen R. Effects of far-infrared sauna bathing on recovery from strength and endurance training sessions in men. Springerplus. 2015; 4: 321.
3. Sawka M. N., Leon L. R., Montain S. J., Sonna L. A. Integrated physiological mechanisms of exercise performance, adaptation, and maladaptation to heat stress. Compr Physiol. 2011; 1(4): 1883-928.