HEART RATE VARIABILITY AT REST AND DURING AN ORTHOSTATIC CHALLENGE AT DIFFERENT RANGES OF MxDMn VALUES IN FEMALE SKIERS IN THE TRAINING PROCESS
Authors: Shlyk Natalia 
Published: December 2020

The aim of the study is to analyze the heart rate variability (HRV) and to identify ranges of variability of cardiac intervals (MxDMn) at rest and during an orthostatic challenge, which result in the violation of cardioregulatory systems and decrease in the functional state of female skiers in the training process.

Research methods and organization. We conducted dynamic HRV studies of 35 female skiers, including 12 young women aged 15-17 years in different periods of the training process. The analysis and physiological interpretation of HRV indicators were carried out in accordance with the recommendations of a group of Russian experts, the European Cardiology Society and the North American Society of Electrical Stimulation and Electrophysiology [1996, 2011], as well as Russian researchers [1,3,5,6]. We carried out 351 HRV studies at rest (5 minutes) and during an orthostatic challenge (6 minutes) using the "VARICARD 2.51" device and the "VARICARD MP" program in the morning before another training session. Using the "VARICARD MP" program allowed us to simultaneously register cardio intervals in four athletes.

Results of the research. We paid particular attention to the variation range of cardiac intervals (MxDMn) during the individual analysis of HRV indicators in female skiers. The functional state of cardioregulatory systems at rest and during an orthostatic challenge was evaluated for different ranges of MxDMn values: <150 ms, 151-250 ms, 251-350 ms, 351-450 ms, 451-550 ms, 551-650 ms, and >650 ms. The paper contains tables with different numbers of optimal and adverse response to an orthostatic challenge in adult and young female skiers with different MxDMn values. At the same time, we paid particular attention to young female skiers who had equal training regime in the analysis of MxDMn values. The paper demonstrates the individual dynamics of MxDMn indicators at rest and during an orthostatic challenge in young female skiers during different periods of the training process. The research revealed that the smallest and largest MxDMn values cause the deregulation process at rest and the deterioration of vegetative reactivity during orthostatic testing. We revealed MxDMn values of female skiers in the range from <100 ms to >600 ms after the same training day before another training session. It indicates different activation of the sinus node control mechanisms and the body recovery processes. The paper contains the outcomes of dynamic HRV studies in different female skiers who had minimal or maximum MxDMn values at rest and adverse response to an orthostatic challenge during different periods of the training process. We demonstrated the outcomes of MxDMn values in an overtrained female skier during the transition of heart rate control mechanisms from a pronounced predominance of the autonomous regulation circuit in the preparatory period to a pronounced predominance of the central regulation circuit in the competition period. The paper contains the figures of cardiointervalograms, HRV and ECG scatergrams at rest and during an orthostatic challenge at different values of the variational range of cardiointervals (MxDMn).

Conclusion. The research revealed an important role of identification of the ranges of variability of cardiac intervals (MxDMn) in the individual HRV analysis in the training process of female skiers for a more accurate assessment of the cardioregulatory system status and the sinus node functioning. The predominant type of vegetative regulation and orthostatic sampling play a great role in determination of the origin of MxDMn indicators at rest. We identified the ranges of MxDMn values at rest and during an orthostatic challenge in young female skiers, which result in deregulatory manifestations, vegetative reactivity and recovery processes disorders leading to overtraining.

We identified the optimal values of the range of MxDMn values for young female skiers, which are common for the moderate prevalence of the autonomous regulation circuit.