The Results of the Study and their Discussion

Comparison of the Medians Of 15 Clino- Indicators of HRV ET ESRT and YSRT for the Entire Preparatory Period (June-November) and for Monthly

In general, a comparison of the medians of clinio- HRV indicators in ESRT and in YSRT for the entire period (Table 1, Figure 1) shows that the medians of the 14 indicators differed, at the same time, in 9 of them, reflecting mainly PD of ANS activity, they were higher in ESRT than in YSRT - these are TP, APHF, APVLF, HF%, RRNN, pNN50%, RMSSD, SDNN and MxDMn, and 5 indicators reflecting the activity of the SD of ANS were lower (APLF, LF%, APLF/APHF, HR, SI) than those of the YSRT, and only the median of one indicator did not differ (VLF%). This suggests that in ESRT has a higher effect on PD of ANS, including probably a higher level of NN-ACh, but below effect of SD of ANS (in conditions of clinostasis). Analysis of the TP components shows that HF- waves occupy the first place in ESRT, VLF- waves occupy the second place, and LF-waves occupy the third place (APHF>APVLF>APLF), while YSRT has VLF- waves in the first place, LF- waves in the second place, and HF-waves in the third place (APVLF>APLF>APHF).

This indicates that in the conditions of clinostasis, in ESRT is dominated by the effect of PD of ANS on heart activity, and to a lesser extent by SD of ANS, and in YSRT the effect of SD of ANS on the heart is higher than the effect of PD of ANS. In each of the six months of the preparatory period (Table 1, Figure 1) the medians of the 4 clino-HRV indices (HF%, RRNN, pNN50%, RMSSD) in ESRT were higher than in YSRT, and the median HR was lower the medians of the remaining 9 indicators of clino-HRV in ESRT and in YSRT did not differ in any of the months, although there were differences in general over the entire period. In particular, the medians of such indicators as TP, АPVLF, SDNN, MxDMn differed statistically significantly only in June and July, which was not observed in the remaining four months of the preparatory period. There were no differences for the median APHF in June and October, for the median LF% in August, and for the median APLF/APHF - in June and August, for the median SI - in October. For median differences of АPLF were not observed in all 6 months, but were present for the entire period as a whole. At the same time, the median of VLF% for both ESRT and YSRTS was the same in each month and for the entire period as a whole.

So, these results confirm the literature data [6,7,10-14] that ESRT, in comparison with YSRT in clinostasis conditions, has higher the median indicators reflecting the activity of PD of ANS and lower the median of indicators, which reflecting the activity of SD of ANS. This is consistent with the assumption that as the experience of skiing increases and, consequently, as athletic skill increases, the influence of PD of ANS on the activity of the heart increases and at the same time an anti-apoptotic system is formed in it, the component of which is NN-ACh. It is obvious that PD of ANS together with NN-ACh reduces the manifestation of the activity of SD of ANS in conditions of clinostasis (additional evidence of this assumption is given below), although it is precisely due to the high activity of SD of ANS that it is possible to achieve high athletic results in cross-country skiing.

Monthly Dynamics of Median Clino-HRV Indicators During the Preparatory Period in ESRT and YSRT Groups

During the preparatory period, which takes six months in a row, the dynamics of the medians of 10 indicators (out of 15) for ESRT and for YSRT were different (Table 1, Figure 1) and at the same time, in each of the groups (ESRT, YSRT), it depended on the amount of training load, which changed in each microcycle, as noted in the section “Research methods”. Thus, in ESRT, the medians of 6 indicators (TP, LF%, pNN50%, SDNN, MxDMn, and SI) remained stable throughout the 6 months of the preparatory period, and the medians of 9 indicators changed during the preparatory period, including the medians of APHF, APVLF, VLF%, APLF, APVLF/APHF, HR and RMSSD, and the medians of HF% and RRNN increased. In particular (tab. 1), the median of АPHF decrease by 5142 to 3264 mc2, it is on 35%, in september; median of АPVLF decreased by 3726 to 1711 mc2. (it is on 35% in October); median of VLF% decreased by 35.6% to 25.0% (october); median of АPLF decreased by 2300 ms2 to 1316 ms2 (it is on 43%, october); median of АPLF/АPHF decreased by 0.48 s.u. up to 0.34 s.u. (it is on 0.1 s.u., october); median of HR decreased by 43.2 b/min to 39.8 b/min (it is on 8%, november) and the median of RMSSD decreased by 129 ms to 100 ms (it is on 22%, september).

The median of HF% increased from 45% to 56.5% in october, and the median RRNN increased from 1388 ms to 1506 ms, i.e., оn 8.5%, in november. Note that a decrease in the medians of APHF, RRNN and RMSSD indicates a decrease in the effect of PD of ANS and NN-ACh on the heart, while an increase in the medians of HF% and RRNN and a decrease in the medians of APLF/APHF and HR, on the contrary, indicate an increase in the effect of PD of ANS, while the absence of changes in the medians of TP, pNN50%, SDNN, MxDMn, and SI speaks about maintaining influence PD of ANS on cardiac activity. These data allow us to conclude that during the preparatory period, ESRT retains a high activity of PD of ANS and, probably, a high level of synthesis of NN-ACh. At the same time, in conditions of clinostasis, the high activity of the SD of ANC, which is typical for elite skiers in competitive conditions, does not significantly effect on the clino-HRV indices, which is probably explained by the inhibitory effect of PD of ANC and NNACh. The question of the reasons for the decrease of the medians of such indicators as АPHF, АPVLF and VLF% in the ESRT in the preparatory period remains open. It is possible that this is due to the fact that during training NN-ACh is used as an anti-apoptotic agent and therefore the content of NN-ACh temporarily decreases, which is reflected in a decrease in the medians of these indicators, which, in our opinion [7], most reflect the level of synthesis of NNAch.

Unlike ESRT, only three indicators change during the preparatory period for YSRT - LF%, HF% and APLF/APHF. At the same time, the median of HF% decreased from 35.3% to 22.6% (in september); the median of LF% increased from 26.3% to 37.7% in november, and the median of APLF/ АPHF increased from 0.76 c. un to 1.30 c. un in november. The remaining 12 indicators of clino- HRV in YSRT did not change throughout the entire preparatory period. This suggests that the activity of PD of ANS and, probably, the level of synthesis of NN-ACh during the preparatory period in YSRT remains stable, but lower than in ESRT, and also suggests that in conditions of clinostasis the ability of PD of ANS and NN-ACh is probably insufficient to inhibit activity of SD of ANS. This is partially indicated by data according to which, during the preparatory period, both in ESRT and in YSRT experienced an increase in the mediansn of APLF, LF% and APLF/APHF, reflecting the activity of SD of ANS, but at the same time, this growth was less pronounced in ESRT than in YSRT. So, in ESRT the median of APLF increased from 2300 ms2 (June) to 2912 ms2 in august; i.e., оn 26.7% (p > 0.05), and in november it even decreased to 1360 ms2 (p < 0.05), and in YSRT it increased from 1740 ms2 (in June) to 3037 ms2 (in November), i.e., on 77.4%.

The median LF% in ESRT increased from 21.0% (June) to 21.8% in November, i.e., on 0.8% (p > 0.05), and in YSRT it increased from 26.3% (June) to 37.7% (November), i.e., on 11.4% (p < 0.05). Median of APLF/АPHF in ESRT increased from 0.48 c.un. to 0.56 c.un. (November), i.e., on 0.08 c.un. (p < 0.05), and in YSRT it increased from 0.76 c.un. (June) to 1.30 c.un. (November), i.e., on 0.54 c.un. (p < 0.05). We do not exclude that in conditions of clinostasis, the high activity of PD of ANS and the high level of production of NN-ACh, characteristic for ESRT, suppresses the effect of SD of ANS on cardiac activity to a greater extent than in YSRT, in which the intensity of synthesis of NH-AH is probably lower than in ESRT. This conclusion is also confirmed by the fact that, in general, for the entire preparatory period, as noted above, the medians LF%, APLF/APHF, HR, and SI were higher in YSRT than in ESRT. So, the results of our research indicate differences in the dynamics of the median of clino-HRV iundices in ESRT and in YSRT during the 6-month preparatory period. In our opinion, these differences are explained by the different levels of synthesis of NN-ACh, which is most likely higher in ESRT than in YSRT. Therefore, the difference we have identified between ESRT and YSRT can be regarded as another indirect evidence of the presence of NN-ACh synthesis in the heart of a person exercising endurance.

It is important to emphasize that the medians of the 5 indicators (TP, pNN50%, SDNN, MxDMn, and SI) did not significantly change during the preparatory period for either ESRT or YSRT, although the medians of these indicators for ESRT were statistically significantly higher than for YSRT. So, initially, the median TP for ESRT was 10,862 ms2, and for YSRT it was 7,101 ms2; the median of pNN50% was 70.1% and 48.9%, respectively, the median of SDNN was 112 ms and 85 ms, the median of MxDMn was 584 ms and 492 ms, and the median of SI was 13.1 c. un. and 28.7 c. un. respectively. Obviously, these indicators, unlike APHF, APVLF, VLF% reflect mainly the activity of PD of ANS, and to a lesser extent reflect the level of NN-ACh.

So, during endurance training, the activity of SD of ANS and PD of ANS increases, while the increase in activity of PD of ANS is probably associated with an increase in the production of NNACh, which increases its effect on the heart and simultaneously (together N-Ach of vagus) reduces the manifestation of SD of ANS activity in the conditions of clinostasis. However, the production level of NN-Ach in YSR is still not high enough, i.e., it is not able to suppress the activity of the SD of ANS in conditions of clinostasis.

The question of why it was not possible to record an increase in activity of PD of ANS and increase of level synthesis of NN- ACh in YSRT during the preparatory period remains open. Perhaps this growth occurs during the transition period, when the volume of training loads decreases and the stress associated with the expectation of competition decreases, which contributes to the synthesis of NN-AСh.

The Dynamics of the Clino-HRV Indicators of the Elite Skier K.D. for 7 Months from the Moment of the Forced Cessation of Training Loads

The data presented in Table 2 and Figures 2 and 3 show that of the 15 HRV indicators recorded in clinostasis, the medians of 10 indicators are statistically significantly decreasing by October 2024. These are TP (by 62%), APHF (by 71%), HF% (by 10%), АPVLF (by 52%),), АPLF (by 67%), RRNN (by 18%), pNN50% (by 24.9%), RMSSD (by 51%), SDNN (by 43%) and MxDMn (by 50%). At the same time, the medians of 3 indicators increase, including VLF% (by 5.4%), HR (by 8.8 beats per minute), and SI (by 38 c.un), and only the medians of two indicators do not change, including LF% (21.2-21.1) and APLF/APHF (0.61-0.63). Obviously, the longer the period of cessation of exercise, the more pronounced the decrease in the medians of 10 indicators (TP, АPHF, HF%, APVLF, APLF, RRNN, pNN50%, RMSSD, SDNN and MxDMn) and the increase in the medians of 3 indicators (VLF%, HR and SI). All this can be explained by a decrease in PD of ANS activity and, probably, a decrease in the intensity of NN-ACh synthesis in an elite skier. The question of to what level the decline in production of NN-Ach occurs remains open, since our judgment is based only on data on the values of HRV indicators. We believe that even 7 months after the cessation of training, the synthesis of NN-ACh in an elite skier is still preserved, but its level is significantly reduced.

Indeed, in October 2024, the median of 4 indicators (LF%, АPLF/АPHF, RRNN, HR) in K.D. were between the medians of appropriate indicators in ESRT and YSRT. Thus, the median of LF% for ESRT was 16.3%, for YSRT - 24.4%, and for K. D - 21.1%; the median of APLF/APHF for ESRT was 0.34 c. un., for YSRT - 0.84 c. un. and for K. D - 0.63 c. un; the median of RRNN, for ESRT was 1440 ms, for YSRT - 1038 ms, and , for K. D - 1197 ms (Figure 2); the median heart rate for ESRT was 42.0 beats/min, for YSRT - 51.7 beats/min, and for K. D - 50.1 beats/min. However, the medians of 9 other clino- HRV indicators in K.D. are lower than in ESRT and YSRT. These are:
1) the median of TP for ESRT was 8612 ms2, for YSRT - 7705 ms2, for K.D. - 3682 ms2 (Figure 3);
2) the median of АPHF for ESRT was 4102 ms2, for YSRT - 3747 ms2, and for K.D.- 1141 ms2;
3) the median of HF% for EST was 56.5%, for YSRT - 43.6%, and for K.D. - 31.0%;
4) median of АPVLF for ESRT was 1711 ms2, for YSRT - 2627 ms2, and for K.D. - 1586 ms2;
5) median of APLF for ESRT was 1316 ms2, for YSRT - 1734 mc2, and for K.D. - 752 mc2;
6) the median of pNN50% for ESRT was 71.4%, for YSRT - 51.7%, and for K.D.- 45.4%;
7) the median of RMSSD for ESRT was 118 ms, for YSRT - 80 ms, and for - 58 ms;
8) the median of SDNN for ESRT was 91 ms, for YSRT - 88 ms, and for K.D.- 58 ms;
9) the median MxDMn for ESRT was 529 ms, for YSRT - 485 ms, and for K.D - 305 ms . And only the median of the stress index (SI) was higher in K. D (49 c.un). than in ESRT (16.1 c.un) and YSRT ( 26.9 c.un ) All this means that the synthesis of NNAСh in К.D. through the 7-month «workout-free» period has been significantly reduced, but it is probably still happening.

Note: * - the differences between the months and, in general, for the entire preparatory period between the groups of athletes are statistically significant, p< 0,05; the numbers in the “Difference” lines reflect the month with which the indicator in this month of the preparatory period differed statistically significantly (p < 0.05, according to the Mann-Whitney criterion) from the indicators of other months of this period, and the dash indicates that there are no differences. The interpretation of HRV indicators is given in the section “Research methods”; -c. un - conventional units; b/min - beats per minute.

Noted: 1 - uppercase numbers indicate the month with which the indicator in this month differs statistically significantly (according to the Mann-Whitney criterion, p < 0.05) from the indicators of other months; TDE_1-5 - total duration of exercise, minutes/day, including aerobic loads (working pulse of zones 1-3) and anaerobic loads ((working pulse of zones 4 and 5).

Note: the dash is the absence of data; the interpretation of HRV indicators is given in the section “Research methods”.

A comparison of the HRV values of a skier K.D. jumper recorded in October 2024 with similar HRV indicators of nonathletes whose cardiontervalography was recorded in clinostasis using an intervalocardiograph of the same brand (Neurosoft) as in our study showed (Table 3) that, indeed, even in October 2024, the synthesis of NN-ACh takes place, although its level is much lower than in the presence of training. Such a comparison was carried out with data on non-athletes with clino-HRV (university students), in whom clino-HRV was registered in both phases of the menstrual cycle [10], as well as with data on 25-year-old male contractors [11] and 29-year-old employees of the firm “Neurosoft” (men and women) [11]. When comparing with the data from [10], it was found (Table 3), that, judging by the values of four indicators (RRNN, HR, pNN50 and SI), reflecting the activity of PD of ANS and probably the synthesis of NN-ACh, in the skier K.D. the synthesis of NN-ACh persists even 7 months after the cessation of training In particular, the median of RRNN and of pNN50% in K.D. were higher than in women (1197 ms versus 860 ms and 45.4% versus 36.7%, respectively), and the medians of HR and of SI were lower than in women (50.1 beats per minute versus 71.2 beats per minute, respectively, and 49 c. ub. against and 54.8 c. un. However, K.D compared to women had lower values of such indicators as МxDMn (305 ms versus 432 ms), SDNN (58 ms versus 75 ms), и RMSSD (58 ms versus 79.5 ms). This indicates a lower activity of PD of ANS and, consequently, a low level of synthesis NN-ACh by cardiomyocytes in K.D. (October 2024). When compared with the data [11] obtained during the examination of contract workers (Table 3) it was shown that their values of a number of indicators (APHF, HF%, APLF, LF%, RMSSD, SDNN) were approximately the same as those of athlete K.D. (October 2024). Indeed, the value of АPHF for contractors was 1010 ms2, for K.D. - 1141 ms2; the value of HF% value, respectively, 36.1% and 31.0%; the value of APLF value, respectively, 745 ms2 and 752 ms2; the value of LF%, respectively, 24.4% and 21.1%; the value of RMSSD, respectively, 48.6 ms and 58 ms; the value of SDNN -53.9 ms and 58 ms, respectively However, the values of such indicators as TP, VLF, VLF%, pNN50% for K.D. were significantly higher, and the values of heart rate was lower than for contractors. Indeed, the TP values for K.D. were 3682 ms2 versus 2815 ms2 for contractors; for values of APVLF, respectively, 1586 ms2 versus 744 ms2, for values of VLF%, respectively, 40.8% versus 33.4%; for values of RRNN, respectively, 1197 ms versus 914 ms; for values of pNN50%, respectively, 45.4% versus 31%; for values of HR, respectively, 50.1 versus 65.5 beats/min. All this suggests that 7 months after the cessation of training, in the athlete K.D. retains the synthesis of NH-ACh, although its level is much lower than that of the during his training.

Compared with the data [11-14] obtained during the survey of Neurosoft employees, it is shown (Table 3) that the values of TP, APHF, APLF, APVLF, RRNN, pNN50%, RMSSD, SDNN were higher in K.D, and the value of APLF/APHF is lower than that of the company’s employees. Indeed, the values for TP in the K.D, remained 3682 ms2 versus 1684 ms2 for the company’s employees; for АPHF - 1141 ms2 versus 528 ms2, respectively; for АPLF 752 ms2 versus 437 ms2, respectively; for АPVLF - 1587 ms2 versus 476 ms2; for RRNN- 1197 versus 980 ms, respectively; for pNN50% - 45.4% versus 13.3%, respectively; for RMSSD, 58 ms versus 34 ms, respectively; for SDNN - 58 ms versus 41 ms, and for the АPLF/АPHF- respectively - 0.63 c.un versus 0.81 c.un ,This also suggests that even 7 months after the cessation of training loads, in athlete K.D. synthesis of NN-ACh persists, although at a lower level than in the presence of training. In general, it can be concluded that in the absence of stimuli that cause synthesis of NN-Ach, for example, accumulation of reactive oxygen species (ROS), or myocardial damage, the synthesis of NN-ACh in elite skiers gradually decreases.At the same time, our data demonstrate that regular physical activity is necessary to maintain athletic vagotonia, including the presence of synthesis of f NN-Ach by cardiomyocytes. It is obvious that the regression of sports vagotonia does not occur instantly, but gradually, as the duration of relative inactivity increases, i.e., the absence of systematic endurance training loads.

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Conclusions

Among elite cross-country skiers of the Republic of Tatarstan (RT) , or ESRT (MS, MSIC), in comparison with young crosscountry skiers of the Republic of Tatarstan, or YSRT, the medians of 14 indicators of clino-HRV differed, while 9 of them, reflecting mainly the activity of PD of ANS, were higher (TP, APHF, APVLF, HF%, RRNN, pNN50%, RMSSD, SDNN, MxDMn), and 5 indicators, reflecting the activity of SD of ANS were lower (APLF, LF%, APLF/ APHF, HR, SI), and only the median of one indicator did not differ (VLF%).This confirms the idea of sports vagotonia as a result of activation of the parasympathetic division (PD) of the autonomic nervous system (ANS) and, probably, increased synthesis of non-neuronal acetylcholine (NN-ACh) by cardiomyocytes of the ventricles of the heart, which occurs as the experience and qualifications of endurance athletes increase.

During the preparatory period, which lasts six months, the medians of 9 clino- HRV indicators change in ESRT, of which the medians of HF% and of RRNN increase, and the medians of APHF, APVLF, VLF%, APLF, APVLF/APHF, HR and RMSSD decrease, while the medians of the remaining 6 indicators (TP, LF%, pNN50%, SDNN, MxDMn, SI) do not change. Consequently, during the 6-month preparatory period, ESRT retains a high activity of PD of ANS and, probably, a high level of synthesis of NN-ACh, while in conditions of clinostasis, the high activity of SD of ANS, which is typical for elite skiers in competition conditions, does not significantly affect on the indicators of clino-HRV, which is likely it is explained by the inhibitory effect of PD of ANS and NN-ACh

Unlike ESRT at YSRT only medians of 3 indicators (from of 15) of clino-HRV change during the preparatory period - median of HF% decreases, and the medians of LF% and APLF/APHF - increasing. This suggests that the activity of PD of ANS and, probably, the level of NN-Ach synthesis during the preparatory period in YSRT remains stable, but lower than in ESRT, and also that in conditions of clinostasis in YSRT the ability of PD and NNACh is probably insufficient to inhibit SD of ANS.

The difference in changes in the medians of clino-HRV in ESRT and YSRT during the preparatory period indicates a significant difference in the mechanisms of regulation of cardiac activity between these groups, which is probably due to a higher level of synthesis of NN-ACh in elite skiers. The revealed difference also indicates that the formation of sports vagotonia, i.e., an increase in activity PD of ANS and synthesis of NN-ACh occurs gradually over many years under conditions of continuous training process

In an elite skier, after 7 months from the moment of forced cessation of training loads, the medians of 10 indicators of clinical HRV (TP, АPHF, HF%, АPVLF, АPLF, RRNN, pNN50%, RMSSD, SDNN, MxDMn) decrease statistically significantly; the medians of 3 indicators (VLF%, HR, SI) increase, and only the medians of the 2 indicators (LF%, APLF/APHF) do not change. It has been shown that with an increase in the “off-load” period, the effect of PD of ANS on heart function decreases in an elite skier and, probably, decreases the intensity of NN-ACh synthesis.

However, even 7 months after the cessation of training, the synthesis of NH-ACh in an elite skier is probably still preserved, albeit at a lower level. This is confirmed by the fact that in October 2024 (the last month of follow-up), the medians of 4 HRV- indicators (LF%, APLF/APHF, RRNN, HR) were between the medians of the corresponding ESRT and YSRT indicators, although the median of 9 HRV-indicators (TP, APHF, HF%, APVLF, APLF, pNN50%, RMSSD, SDNN, MxDMn) were lower in K.D. and the median SI was higher than in ESRT and YSRT. The partial preservation of the synthesis of NN-ACh in the elite skier K.D. (October 2024) is also evidenced by the results of comparison with literature data on the values of HRV indicators in non-athletes.

In general, the results of the study allow us to conclude that the regression of sports vagotonia in the conditions of complete absence of training loads occurs over the course of 7 months, i.e., much faster than the formation of sports vagotonia, which takes many years.

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The Authors’ Contribution to the Publication

S D.A. Kataev - registration of a cardio interval gram (CIG) in the field, analysis of its parameters, writing an article, literature analysis; V.I. Tsikin - head of scientific work, literature analysis, work on the article; S.I. Trukhina, A.N. Trukhin - scientific editing, preparation of the article and the necessary documentation

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Ethical Standards

All studies were conducted in accordance with the principles of biomedical ethics formulated in the Helsinki Declaration of 1964 and its subsequent updates and approved by the local Bioethical Committee of Vyatka State University (Kirov). (Protocol No. 1, dated 17.01.2020).

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References

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