Dr. Med., Professor A.L. Pokhachevsky^{1, 2}
PhD, Associate Professor A.I. Filipchenko¹
Postgraduate P.A. Kulagin²
Associate Professor V.N. Pozhimalin³
PhD, Associate Professor A.B. Petrov^4
1Sechenov First Moscow State Medical University of Russia of the Ministry of Health of Russia, Moscow
²Ryazan State Medical University of the Ministry of Health of Russia, Ryazan
³Academy of the Federal Penitentiary Service of Russia, Ryazan
⁴State Lesgaft University of Physical Culture, Sports and Health, St. Petersburg

Keywords: physical activity, pNNx, stress test, heart rate.

Introduction. The study of the cardiorhythmogram (CRG) of the stress test in a group of unsportsmanlike youth revealed the peculiarities of the formation of stress tolerance.
The aim of the study is to discover the crucial interrelations of markers of physical performance and variability of the CRH stress test in a group of young people who are not related to systematic physical exertion.
Methodology and organization of the study. The maximum bicycle ergometric testing was carried out according to an individual protocol [2]. The sequential time series of cardiointervals –CI) - cardiorhythmogram (CRG) was divided into periods: pre-start (PS) - (30 seconds) preceding the beginning of ergometry; start (ST) – (30 seconds) from the beginning of rotational locomotion with a load of 50 W; for 1, 2, 3, etc. minutes of the load period. Nonparametric criteria (Statistica 10.0) were used for statistical processing. The KRG of each of the periods was subjected to linear mathematical modeling (LMM) and pNNx analysis. LMM for each of the periods was carried out according to the formula: Y=aX+b, where X is the ordinal number of CI in the KRG time series, Y is the duration of CI, "a" is the model parameter characterizing the rate of variability of the time series and "b" is the model parameter determining its constant component.
pNNx is the percentage of CI pairs with a difference of Xms or more to the total number of CI in the array. Since the value of the absolute difference of neighboring CI in the study group does not exceed 20 ms, pNN (2-20) were studied in 2 ms increments.
The results of the study and their discussion. Significant connections of pNNx with maximum physical performance were revealed. The negative value of correlation relationships emphasizes that the lower the value of the pNNx indicator takes, the greater the level of the maximum of the FN will be reached. The present trend is statistically significant for PS, CT and is manifested by pNN (2-16). In turn, the correlation level for all X is actually stable (-0.6- (-0.64)). The relationships for 1-4 min of load have their own characteristics. For 1 min. maximum negative correlation values are obtained for pNN12 (-0.5), 2 min – pNN20 (-0.46) for 3 minutes pNN18 (-0.36).
It is known that the presence of large amounts of variability pNNх is used for maximum health – while correlation for pNNх contributing to this realization should be positive [2, 3]. In this case, there is a very negative trend for the entire range pNNх. For the present sample, this can only be explained by the minimum initial volume and assortment pNNx.
Conclusions. The peculiarities of the formation of physical performance in the study group are caused by the total insufficiency of the variability of CI (initially a small level of pNNx), which exhausts its reserves by 1 min of load, and not by a fundamentally different pattern of the formation of physical performance.

Literature

1. Lapkin M.M., Birchenko N.S., Petrov A.B. Prognostic potential of the loading cardiorhythmogram of the early adaptation period // Man. Sport. Medicine. – 2018. – № 1 (18). – Pp. 46-59.
2. Prognostic potential of the time series of the stress test cardiorhythmogram / M.M. Lapkin, E.A. Trutneva, A.B. Petrov et al. // Human Physiology. - 2019. - Vol. 45, No. 3. - pp. 48-60.
3. Patent 2613937 of the Russian Federation. A method for determining the potential level of physical performance during submaximal load testing / M.M. Lapkin, Yu.M. Reksha. No. 2015136686; application No. 29.08.2015.