Introduction. Heart rhythm, reflecting neurohumoral influences, is a marker of the body's adaptive reactions [1-3].

The aim of the research  is to reveal the connections between spectral and pNNx characteristics of heart rhythm.

Methods and organization of the research. A youth sample of 54 people (18-23 years old) with mixed levels of physical activity was studied. In the clinostasis state, the following were studied: total power (TP) of the heart rhythm spectrum; high-frequency (HF), low-frequency (LF), and humoral-metabolic (VLF) components; the pNNx indicator – the percentage of pairs of RR intervals with a difference from 10 to 100 ms and more to the total number of RR intervals in the array. Statistical processing: Statistica 10.0, Excel 2021; correlations – Spearman; cluster analysis (K-means method). Statistical significance – p<0.05.

Results and discussion. Cluster analysis identified two homogeneous groups from the mixed sample, which differ significantly in physical activity: the 1st – 36 people not involved in systematic physical loads; the 2nd – 18 people systematically training 5 or more times a week. The frequency characteristics of the heart rhythm of the sports group significantly exceed those of the non-sports youth group: in terms of TP (6730 vs 2380), LF (1573 vs 777), HF (2150 vs 635). The pNNx indicators in clinostasis consistently decrease in the pNN10-90 series at a significantly different rate: pNN10 (75% vs 86%), pNN50 (10% vs 37%), pNN80 (0.8 vs 18). The difference in the sports group lies in the significant predominance of long pNNx and in the amplification of these differences in the increasing series of pNN10-100 durations.

The total power of the spectrum in the mixed sample is determined by a gradually increasing connection with pNNx in the 10-100 ms series, while in the non-sports youth group the pNN40-80 ms segment is of decisive importance, and in the athletes' group there are no connections. Thus, in the mixed sample, the heterogeneity of the studied population is manifested by the influence of longer pNNx (from the athletes' group). At the same time, in the non-sports youth group, adaptive reserves can only rely on the part of pNNx that it has – 40-80 ms. The absence of significant connections with TP in the athletes' group is associated with reaching the maximum population values of this indicator, when changes in pNNx in any register will not lead to its increase, but can change intraspectral relationships in the direction of fast mechanisms.

The fastest adaptive HF mechanisms in the mixed sample demonstrate the maximum high level of connection with the entire range of pNN, while strong connections are revealed in both cluster groups; however, if in non-sports youth they are associated with shorter pNN10-50 ms, then in athletes – 40-80 ms and more.

The presence of positive connections of pNN with the sympathetic and humoral-metabolic component in the combined group is also associated with its heterogeneity and is determined by the presence of such connections only in the non-sports youth group, while in the sports group they are either absent (LF), or manifest themselves as a pronounced inversion (-0.88) for VLF.

Conclusions. The formation of endurance significantly changes the pattern of correlations between the spectral characteristics of heart rhythm and pNNx: in the sports group, the predominant long pNNx provide connections with fast regulatory mechanisms (HF) and actually eliminate slow ones (VLF); in the comparison group, short and medium pNNx, on the contrary, additionally attract slow adaptive mechanisms (LF, VLF).

References

1. Lapkin M.M., Trutneva E.A., Petrov A.B., Shuliko Yu.V., Kalinin A.V. Prognosticheskiy potentsial vremennogo ryada kardioritmogrammy stresstesta [Prognostic potential of the time series of the stress test cardiorhythmogram]. Fiziologiya cheloveka. 2019. V. 45. No. 3. Pp. 48-60.
2. Lapkin M.M., Trutneva E.A., Kalinin A.V., Lavrukhina G.M. Sistemnaya organizatsiya fiziologicheskikh funktsiy, obespechivayushchaya maksimalnuyu fizicheskuyu rabotosposobnost [System organization of physiological functions providing maximum physical performance]. Chelovek. Sport. Meditsina. 2022. V. 22. No. S2. Pp. 37-45.
3. Mikhaylov V.M. Variabelnost ritma serdtsa (novyy vzglyad na staruyu paradigmu) [Heart rate variability (a new look at the old paradigm)]. Ivanovo: Neyrosoft. 2017. 516 p.

No. 7, pp. 56–56

Received: 10.04.2026 | Published: 26.06.2026

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