Regression of Sports Vagotonia

Registration of Heart Rate Variability (HRV) in clinostasis conditions revealed that after 7 months from the moment of the forced complete cessation of all training loads, the median of 10 indicators (out of 15)-clino-HRV (TP, APHF, HF%, APVLF, APLF, RRNN, pNN50%, RMSSD, SDNN, and MxDMn) statistically significantly decrease to the level typical for non-athletes, while the medians of 3 indicators (VLF%, HR, SI) increase and only the medians of 2 indicators (LF%, AMLF/AMHF) do not change. During the same period, 11 indicators of ortho-HRV decreased to the level typical for non-athletes (TP, APHF, HF%, APVLF, VLF%, APLF, RRNN, pNN50%, RMSSD, SDNN and MxDMn) and the medians of 4 indicators (LF%, APLF/APHF, HR and SI) increased. Heterochrony is characteristic of changes in the indicators of clino-and ortho-HRV. The first statistically significant changes in the median of HRV-indicators are observed a month after the cessation of training loads and they increase gradually, reaching a plateau after 2-5 months. The cessation of training loads was accompanied by a decrease in the activity of the Sympathetic Division (SD) of the Autonomic Nervous System (ANS) and especially, a decrease in the activity of the Parasympathetic Division (PD) of the ANS, including, probably, a decrease in the synthesis of non-neuronal acetylcholine (NN-ACh), the presence of which, however, even after 7 months of cessation of training is still present in K.D., although its level is significantly reduced SD. So, if, as is well known, long-term aerobic training loads are required for the formation of sports vagotonia, then a relatively short period of time is sufficient for its regression, judging by the data of the elite skier K.D.-no more than 7 months in the complete absence of endurance training.

Keywords:Heart rate variability; Clinostasis; Active orthostasis; Cross-country skiers; Autonomic nervous system; Parasympathetic and sympathetic divisions; Non-neuronal acetylcholine; Regression of sports vagotonia

It is known that long-term continuous training loads of large volume with relatively high intensity are required to form a high level of endurance [1,2]. One of the proofs of this position is the fact that the winners of the World Championships and the Winter Olympic Games in cross-country skiing, namely in the 50km ski marathon, are athletes whose average age is 26-29 years and who have a long experience in this sport [1]. It is shown that only 0.83% of cross-country skiers aged 15-16 who became winners and prize-winners of All-Russian competitions among boys aged 15-16 fall into the list of the 40 best male skiers in Russia, and only 0.56% of them compete at the World Cup [2]. Earlier, based on literature data [3-5] on the ability of the human and animal hearts to synthesize non-neuronal ACh (NN-ACh), as well as on the basis of the values of Heart Rate Variability (HRV) indicators of ski racers, it was suggested that sports vagotonia, characteristic of athletes training for endurance, including for cross-country skiers, it is caused not only by an increase in the activity of the Parasympathetic Division (PD) of the Autonomic Nervous System (ANS), but also by the ability of ventricular cardiomyocytes to synthesize non-neuronal acetylcholine, or NN-ACh [6,7]. At the same time, NN-ACh is considered as a component of the anti-apoptotic system, due to which the heart, doing a great job of creating the necessary blood flow (under the influence of catecholamines activating beta1-AR of the myocardium), remains viable, despite the presence of high levels of Reactive Oxygen Species (ROS) and the damaging effects of catecholamines [6,7].

The purpose of this article is to further confirm the hypothesis of the presence of NN-ACh synthesis in the myocardium based on the analysis of the dynamics of the medians of 15 indicators of Heart Rate Variability (HRV), recorded sequentially in conditions of clinostasis and then in conditions of active orthostasis in the elite skier-racer K.D., master of sports, the first author of the article, after a forced complete cessation training loads (detrainment), which occurred at the end of March 2024, for 7 months, i.e. up to and including October 2024. A working hypothesis is the assumption that the cessation of training loads (detrainment, or maladjustment) in an elite ski racer causes a gradual but relatively rapid decrease in the activity of the Sympathetic Division (SD) of the Autonomic Nervous System (ANS) and its Parasympathetic Division (PD), including by reducing the synthesis of NN-ACh, judging by the change in the values of numerous HRV indicators. It is well known that the indicators of clino-HRV and ortho-HRV reflect the activity of SD and PD, and in our opinion [6,7], they also reflect the influence of NN-ACh on heart activity.

Moreover, the influence of NN-ACh is probably especially pronounced when comparing the corresponding HRV indicators recorded in humans sequentially, first in conditions of clinostasis (clino-HRV) and then in conditions of active orthostasis (ortho- HRV), i.e. during the implementation of the Prevel reflex, since, according to our assumption, the higher the activity of ANS and the higher the level of synthesis of NN-ACh by cardiomyocytes, the weaker the activation of ANS during the realization of the Prevel reflex. Therefore, the methodological basis of this study was the analysis of the dynamics of the values of the most commonly used 8 spectral and 7 temporal HRV indicators, recorded sequentially in an athlete under conditions of clinostasis and orthostasis, and the analysis of delta, i.e. the difference between the value of each indicator of clino-HRV and the value of the corresponding indicator ortho-HRV for 7 months of detoxification, i.e. cessation of endurance training.

Elite ski racer KD (Master of Sports since 2012), in the 2018/2019 and 2019/2020 seasons, was a member of the men’s national ski racing team of the Republic of Tatarstan (RT) (hereinafter referred to as the elite skiers of the Republic of Tatarstan, or ESRT). As a graduate student in physiology at Vyatka State University, KD. Studied all 8 members of this team, including himself, which is reflected in a number of publications [6-12]. In March 2024, being one of the “playing” coaches of the Tatarstan youth national team, consisting of 11 athletes (hereinafter referred to as YLRT) and in whom he also registered HRV, athlete K.D. was forced to stop training due to damage to the tendons of the adductor muscles of the left thigh, which is known to be characteristic [13] for Adduktor-Rectus-Symphysis-Syndrome (ARS). However, due to the personal use of the Neurosoft interval cardiograph (Ivanovo) and previous experience as a graduate student, K.D. conducted HRV self-registration in April, June, August and September (respectively, on 19, 22, 28 and 14 days of each month, i.e. a total of 85 HRV registrations. In each study, 5-minute interval cardiography (CIG) was performed first in a clinostatic setting, and then for the next 5 minutes in an active orthostatic position (while the first 10 seconds of this recording were excluded from the analysis).

All CIG variants were implemented (as before) after a night’s sleep, before eating breakfast, in comfortable conditions when using an interval cardiograph of the VNC-Micro brand from Neurosoft (Ivanovo), i.e. an interval cardiograph of the same brand that was previously used in the study of ESRT and YSRT. This made it possible to compare the indicators of clino-and ortho- HRV registered in athlete K.D. After the cessation of training with the corresponding HRV indicators registered in athlete K.D. in 2019 and 2020. Since K.D.’s injury occurred at the end of March 2024, the first three months of observation (April, May, and June) coincided with a transitional period in the training of elite skiers. Therefore, for comparison, the data of the K.D. Obtained during his examination in June 2019 were taken (the “first point of comparison”) and in June 2020 (the “second point of comparison”) were used as a comparison, i.e. during the transition period, during which the volume of training loads carried out at the athlete’s place of residence decreases compared to preparatory and competitive periods conducted in the conditions of training camps (TC). As can be seen from Table 1, the total duration of mixed-type exercise (TD_1-5), judging by the median, the 25^th and 75^th centiles, in K.D in June 2019 was 211.5 (166/269) minutes per day, of which aerobic exercise (TD_1-3) accounted for 201.5 (116/269) min per day and for the proportion of anaerobic loads (TD_4-5)-6.5 (1.2/10) min per day. In June 2020, these values were 101 (85/118), 101 (85/117) and 0, respectively, i.e. anaerobic loads were not included in the training process, and the reduction in training loads during this period was made on the recommendations of the coach due to the continuation of the covid-19 epidemic. This explains the significant differences in the values of HRV indicators for K.D. in June 2019 and June 2020, taken as the “first and second points of comparison,” respectively.

We also note that the indices with the abbreviation TD, i.e. TD_{1- 5}, TD_1-3 and TD_4-5 mean the zones of the working pulse, of which, according to [14], the first three zones (1-3) are zones of aerobic exercise that occur when the working pulse is less than 80% of the maximum heart rate. Zones 4 and 5 are zones of anaerobic exercises, at which the heart rate is above 80% of the maximum heart rate. Therefore, TD_1-5 means the total duration of all types of loads. As you know, elite ski racers have enormous training loads. So, in K.D. During the preparatory period (it lasts 6 months) of the 2019-2020 season, “the first point of comparison”), the volume of loads was 5278km or 375.5h. It is appropriate to note here that K.D. has been involved in cross-country skiing since the age of 10 (since 2003) and since 2005 he has been a regular participant in the TC, i.e. until the sudden cessation of training, his experience in cross-country skiing was 21 years. During the observation period (April-October 2024), K.D. maintained only his household workload. HRV analysis was performed using the Poly spectrum program (Neurosoft, Russia). At the same time, the generally accepted 8 spectral and 7 temporal parameters of HRV were analysed. Among the spectral indicators of HRV are the total power of the spectrum (TP, ms²), or total power; The absolute power (AP. mc²) of fast (HF-) waves, slow (LF-) waves and very slow (VLF-) waves (hereinafter referred to as APНF, APLF and APVLF); The APLF/APHF ratio, the relative power of HF, LF and VLF waves, i.e., the wave power expressed as a percentage of TP (hereinafter referred to as HF%, LF%, and VLF%, respectively).

Among the time indicators, the duration of normal R-R intervals (RRNN, ms) was analysed, which is analogous to heart rate (b/pm); The ratio of consecutive NN intervals, the difference between which exceeds 50ms, as a percentage of the total Number of Normal (NN) R-R intervals (pNN50%); The square root of the average the square of the differences in the values of consecutive pairs of NN intervals (RMSSD, ms); The standard deviation of all NN intervals (SDNN, ms); The variation range (MxDMn, ms), i.e. the difference between the maximum and minimum R-R intervals, as well as the stress index (SI, conl. units), or the voltage index, which was calculated using the formula: IN=AMo/Mo×2MxDMn, where AMo is the amplitude of the mode, i.e. the most common value of the R-R ECG interval, expressed as % of all R-R intervals; Mo is the absolute value of the mode (c) and MxDMn is the variation range, i.e. the difference between the maximum and minimum values of the R-R intervals (c). The assessment of these indicators was formed by summing up the results of individual studies of each month, which is presented in Table 1. All the results were expressed as medians, 25 and 75 centiles [15]. When assessing the differences, the Mann-Whitney criterion was used, considering them statistically significant at p<0.05 [15]. For calculations, including the Pearson correlation coefficient and regression analysis, the BioStat 2009 Professional, 5.9.8 program (Analyst Soft) was used. Research conducted by K.D. in 2019 and 2020, were approved by the local Bioethical Committee of Vyatka State University (Protocol No. 1 dated 17.01.2020).

The main results of the study are presented in Table 1 & 2 and in Figure 1 & 2.

Change in the median values of the clino-HRV of an elite skier K.D. by the end of a 7-month absence of training

The data presented in Table 1 and Figure 1 & 2 show that of the 15 HRV indicators recorded in clinostats, by October 2024, the medians of 10 indicators were statistically significantly lower than those of the corresponding HRV indicators in K.D. in June 2019 (the first point of comparison). Among them-TP (her median has decrease by 9764ms² to 3682ms², that is, by 62%), АPHF (from 3959ms2 to 1141ms2, i.e. by 71%). HF% (from 41.0% to 31.0%, i.e. by 10%), APVLF (from 3333ms² to 1587ms². i.e. by 52%), APLF (from 2188ms² to 732ms². i.e. by 67%), RRNN (from 1452ms to 1197ms, i.e. by 39%), pNN50% (from 70.3% to 45.4%, i.e. 35.4%), SDNN (from 101.5ms to 58ms, i.e. by. 43%) and MxDMn (from 1 605ms to 305msс, i.e. by 16%).

At the same time, the medians of 3 indicators were higher than in June 2019 - these are VLF% (the median increased from 35.4% to 40.8%, i.e. by 5.4%), heart rate (from 41.3 beats per minute to 50.1 beats per minute, i.e. by 8.8 beats per minute, or by 20.1%) and SI (from 11.2 cont. units to 49.2 cont. units, i.e. by 38 cont. units), and only the medians of the two indicators have not changed-these are LF% (21.2-21.1% of TP) and APLF/ APHF (0.61-0.63conl. units). At the same time, the structure of TP- waves has changed-in June 2019 it was presented as APHF>APVLF>APLF, i.e. HF-waves are in 1-st place and VLF-and LF-waves are in 2_nd and 3_rd place, respectively and in October 2024, it is represented as APVLF>APHF>APLF, i.e. VLF-waves occupy the 1st place.

Taking into account the previously suggested assumption that VLF-waves reflect the synthesis of NN-Ach [6], these data allow us to conclude that during the regression of sports vagotonia, the activity of SD of ANS and PD of ANS decreases and probably, the level of synthesis of NN-ACh also partially decreases. It is shown that with an increase in the period of cessation of the load, the degree of change in the medians of the above-mentioned clino-HRV indicators also increases (Figure 1 & 2). Comparison of the median clino-HRV indicators registered at K.D in October 2024 with the corresponding clino-HRV indicators typical for ESRT and YSRT, as well as for athletes of other sports and for non-athletes. The question of the level to NN-ACh production decreases at the end of the 7-month period of complete absence of endurance training remains open, but we assume that the synthesis of NN-ACh in an elite skier K.D. is still preserved, albeit at a lower level. Indeed, in October 2024, the median of 4 indicators of K.D. (RRNN, HR, LF%, АPLF/АPHF) were found between the medians of the clino-HRV indices characteristic of ESRT and for YSRT. Thus, according to our data [12], in these two teams, the values of the clino-HRV indices, which are the average values for all 6 months of the preparatory period, indirectly indicate that the activity PD of ANS and probably the synthesis of NN-ACh in ESRT is higher than in YSRT.

So, the median RRNN in ESRT was 1440ms, in YSRT was 1038ms and in K.D (October. 2024)-1197ms; the median of HR made up accordingly 42.0b/min, 51.7 b/min and 50.1bmin., median of LF%- 16.3%, 24.4% and 21.1%., and median of АPLF/АPHF--0.34con. units, 0.84con. units and 0.63con. units. It should be noted that RRNN and HR reflect, as is known, the effect on the heart according PD of ANS and, probably, NN-Ach and LF% and АPLF/АPHF mainly reflect the effect of SD of ANS.

However, the medians of 9 other clinic-HRV indicators in K.D. were lower than in ESRT and n YSRT. These are the medians of
a. TP: for ESRT-8612ms², for YSRT-7705 ms², for K.D.-3682ms²
b. АPHF-respectively 4102ms2, 3747ms² and 1141ms²
c. HF%-respectively-56.5%, 43.6% and 31.0%
d. APVLF-1711ms², 2627ms² and 1586ms², respectively
e. APLF-1316ms², 1734ms² and 752ms², respectively
f. pNN50%-71.4%, 51.7% and 45.4%, respectively
g. RMSSD-118ms, 80ms and 58ms, respectively
h. SDNN-91ms, 88ms and 58ms, respectively
i. MxDMn-529ms, 485ms and 305ms, respectively

And only the median of SI was higher for K.D. (49conl.units), than for ESRT (16.1conl. units) and YSRT (26.9conl. units). All this indirectly confirms our idea that the synthesis of NN-Ach in K.D. is significantly reduced after 7 months without training loads, but it probably still occurs, albeit at a lower intensity. We compared the values of the clino-HRV indicators of skier K.D. (October 2024) with similar clino-HRV indicators of non-athletes, in whom HRV registration [16] was carried out in clinostats using an interval cardiograph of the same brand (“Neurosoft”), which was used by us. In particular, when comparing with the data obtained from the examination of 25-year-old male contractors [16], it was shown that their values of a number of indicators (APHF, HF%, APLF, LF%, RMSSD, SDNN) were approximately the same as those of PHD (October 2024). Indeed, the values of АPHF for contractors were 1010ms², for K.D.-1141ms²; for HF%-36.1% and 31.0%, respectively; for АPLF-745ms² and 752ms2; for LF%-24.4% and 21.1%; for RMSSD -48.6ms and 58ms; for SDNN-53.9ms and 58ms.

However, the values of such indicators as ТР, АPVLF, VLF%, RRNN and pNN50%were significantly higher for K.D. than for contractors. Thus, the TP value for K.D. was 3682ms² versus 2815ms² for contractors; for APVLF, respectively, 1586ms² versus 744ms², for VLF%, respectively, 40.8% versus 33.4%; for RRNN, respectively, 1197ms versus 914ms; for pNN50%, respectively, 45.4% versus 31%, but the value of heart rate for K.D. was lower than that of the contractors (50.1 versus 65.5 beats per minute). All this suggests that 7 months after the cessation of training, the athlete K.D. retains the synthesis of NN-ACh, although its level is undoubtedly lower than in K.D. in 2019, i.e. in the presence of training. When comparing with the data obtained from the examination of 29-year-old men and women, employees of the firm “Neurosoft” [16], it was shown that the values of TP, APHF, APLF, APVLF, RRNN, pNN50%, RMSSD, SDNN were higher than those of the company’s employees.

Indeed, the TP value for K.D. was 3682ms² versus 1684ms² for the company’s employees; for АPHF, 1141ms² versus 528ms², respectively; for АPLF-752ms² versus 437ms², for АPVLF-1587ms² versus 476ms²; for RRNN-1197ms versus 980ms; for pNN50%- 45.4% versus 13.3%; for RMSSD-58ms versus 34ms; for SDNN- 58ms versus 41ms, respectively. On the contrary, the value of APLF/APHF was lower for K.D. than for employees-0.63conl. units versus 0.81conl. units. This also suggests that even 7 months after the cessation of training loads, at K.D/ synthesis 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 training loads, the synthesis of NN-FCh in the heart of an elite skier gradually decreases. Obviously, the regression of sports vagotonia does not occur instantly, but gradually, as the duration of the absence of systematic endurance training increases, but much faster than the formation of sports vagotonia, which, as noted above, takes years of continuous high-volume training.

The change in the medians of ortho-HRV indicators of an elite skier K.D. by the end of a 7-month absence of training

It was found (Table 1, Figure 1 & 2) that the medians of ortho-HRV indices gradually change during the 7 months of acute cessation of training loads in an elite skier K.D. In particular, in October 2024, the medians of 11 indicators out of 15 indicators of ortho-HRV were statistically significantly lower than the values typical for June 2019. This is
a) TP (its median decreased from 4144ms² to 1708 ms², i.e. by 58.8%
b) АPHF-from 283мs2 to 43мs², i.e. by 84%
c) HF%-from 6.3 to 1.9%, i.e. by 4,4%
d) АPVLF-from 1646ms2 to 776ms², i.e. by 52%
e) VLF%-from 43.5 to 41.0%, i.e. by 2.5%
f) АPLF-from 2267ms2 to 886ms², i.e. by 61%
g) RRNN - from 945ms to 749ms, i.e. by 20.7%
h) pNN50%-from 11.7% to 1.3%, i.e. by 26.3%
i) RMSSD-from 34ms to 15ms, i.e. by 55.9%
j) SDNN-from 65ms to 42ms, i.e. by 35.3%
k) MxDMn-from 325ms to 232ms, i.e. by 28.6%

But at the same time, the medians of 4 indicators in October were higher than the initial ones; this is
a. LF%-an increase from 49.1% to 56.4%, i.e. well. up to 7.3%
b. АPLF/АHHF-an increase from 9. 05c.un. to 26.7c.un. i.e. well. up to 17.5c.un
c. HR --an increase from 63.5b/min up to 80.1b/min, i.e. well. up to 26%
d. SI --an increase from 51.1c.un. up to 142.0c.un. i.e. well. up to 90c.un

Table 1:

Notes: 1)-The numbers in upper case indicate the month with which the indicator in this month differs statistically significantly (according to the Mann-Whitney
criterion, i.e. p<0.05) from the indicators of other months. 2) The HRV delta is the difference between the medians of the corresponding ortho-HRV and clino-HRV
indicators. 3) The interpretation of HRV indicators is described in the section “Research methodology”.

Figure 1:Medians of the absolute power of TP-waves (ma2), the absolute power of HF, VLF and LF waves (ms2; respectively, АPHF, АPVLF и АPLF), the relative (in% to TP) power of these waves (respectively HF%, VLF%, and LF%) and the ratio of APLF/APHF (conl. units), according to cardiointervalogram registration data in conditions of clinostasis (solid curve) and orthostasis (intermittent curve) in K.D. p with training loads, i.e. in June 2019 and June 2020 (dark background of bars) and in the absence of training loads (light background of bars). Note: the * symbol means that the corresponding month differs from the first month (June 2019) statistically significantly according to the Mann-Whitney criterion, p<0.05.

Figure 2:Medians RRNN (ms), heart rate (b/pm), pNN50% (%), RMSSD (ms), SDNN (ms), MxDMn (ms), SI (conl. units), according to cardiointervalogram registration data in conditions of clinostasis (continuous curve) and orthostasis (intermittent curve) at K.D., in conditions of training loads, i.e. in June 2019 and June 2020, (dark background of the bars) and in the absence of 7 training loads (light background of the bars). Note: the * symbol means that the corresponding month differs from the first month (June 2019) statistically significantly according to the Mann-Whitney criterion, p<0.05.

It is important to note that, as noted above, of the 15 indicators of clino-HRV, only two indicators remained unchanged, namely LF% (21.2-21.1% of TP) and APLF/APHF (0.61-0.63conl.units), i.e. exactly those indicators that reflect the activity of SD of ANS. In the same time in the conditions of active orthostasis melians of this indicator increase, in the particulars of median of LF% increased from 49.1% to 56.4%, that is on 7.3% and the median of АPLF/АPHF increased from 9.05conl. units. up to 26.7conl. units. that is, on 17, 5conl.units. This means that upon termination of training, judging by the clino-HRV, the proportion of SD of ANS in the total spectrum, as well as the ratio of SD/PD remains the same as during endurance training, but in conditions of active orthostasis, due to a decrease in the inhibitory effect of NN-ACh on the activity of the SD of ANS, the medians of these two indicators. Which reflect the activity of the SD of ANS, increase. The decrease in the influence of NN-AСh on the on the activity of SD of ANS in K.D (October 2024) also indicates an increase in the median of ortho-HR (from 63.5 to 80.1b/mine, i.e. by 26%) and ortho-SI (from 51.1conl.units to 142.0conl.units, i.e. by 90conl.units). In general, we conclude that the changes in the medians of 15 ortho-HRV indices are explained by a decrease in the activity of SD and PD of ANS, including, probably, a decrease in the synthesis of NN-ACh as indicated by an increase in 4 ortho-HRV indices (ortho-LF%, ortho-APLF/APHF, ortho-HR and ortho -SI).

Comparison of the median of ortho-HRV indices, which registered at K.D in October 2024 with the corresponding ortho-HRV indices characteristic of ESRT and YSLRT, as well as for athletes of other sports and for non-athletes

A comparison of the medians of ortho-HRV in K.D. (October 2024) with our unpublished data on ortho-HRV in ESRT and YSRT, as well as with literature data on the values of a number of ortho- HRV indicators for elite skiers, unskilled skiers, athletes of other sports and non-athletes [16-22], showed that of the 15 ortho-HRV indicators, the presence of NN-ACh-synthesis in K.D in October 2024 indirectly reflects only three indicators, namely ortho-APLF, ortho- RRNN and ortho-HR. Thus, with regard to the median of ortho-APLF, which, as is known, reflects the activity of the SD of ANS, it was shown that in October 2024, the athlete K.D. had 886ms², ESRT had 2496ms2, and YSRT had 1592ms². Ortho-APLF values, according to [17], for hockey players were 2058ms2, or swimmers-1654ms2 and for weightlifters-1735ms2; according to [18], for novice skiers, in particular, sympathectomies, they were 890ms2, for normotonic- 1302ms² and for vagotonic-1950ms²; according to [16], for male contractor they amounted to 1204ms², for non-athletes-1234ms², for track and field athletes-1859ms², for parachutists-1446ms², for professional football players-1404ms² and for 16-year-old hockey players-2165ms²; according to [19], among swimmers (MS, 17- 23 years old)-they amounted to 3771ms². So, K.D. has a median of ortho-APLF much lower than that ESRT and YSRT and lower than that of representatives of other sports and even lower than that of non-athletes.

Indirectly, this means that after a 7-month absence of training, K.D. retain NN-ACh synthesis (although at a lower level than active elite skiers), which, with active orthostasis, inhibits the activation of SD of ANS, i.e. reduces the median ortho-APLF. The median ortho-RRNN, which reflects, as is known, ctivity of PD of ANS, was 749ms for athlete K.D. in October 2024, 906ms for ESRT and 705ms for YSRT. According to [16], ortho-RRNN values for male contractors were 692ms, for track and field athletes-768ms, for parachutists-702ms, for football players-844ms, and for 16-yearold hockey players-755ms; according to [21], for amateurs- halfmarathon runners over 10 years of training, it increased from 765ms to 856ms; according to [22], its values were 915ms for triathletes, and 824ms for CrossFit athletes; according to [20], for elite cross-country skiers from Russia, Norway and Switzerland the ortho-RRNN value varies from 817ms up to 848ms. So, in October 2024, K.D.’s median ortho-RRNN was lower than that of elite skiers and elite marathon runners, but higher than that of young skiers and non-athletes. This indirectly indicates that skiers K.D/have a synthesis NN-ACh, the level of which, however, is lower than that of elite skiers.

The median of ortho-HR, which reflects the effect of PD of ANS on the heart, in the athlete K.D. in October 2024 was 80.1beats/min, for ESRT-66.2beats/min, for YSRT-85.1beats/min. According to [16], the ortho-heart rate values for male contractors were 86.7b/ min, for track and field athletes-78.1b/min, for parachutists-85.5b/ min, for professional football players-71.0b/min, for 16-year-old hockey players-79.5b/min. So, in October 2024, K.D.’s median ortho-HR was higher than that of elite skiers, but lower than that of young skiers and non-athletes. This probably reflects the presence of NN-ACh synthesis in skiers K.D, whose level, however, is lower than that of elite skiers. The medians of the remaining 12 (out of 15) ortho-HRV indicators indicate the absence of NN-ACh synthesis in the athlete K.D. in October 2024. As an example, we will give data on the median of TR. It was 1708ms² for the athlete K.D. (October 2024) 5317ms² for the ESRT and 3241ms² for the YSRT. According to [17], the ortho-TP values for hockey players, swimmers and weightlifters were 4189ms², 2899ms² and 3466ms², respectively; according to [18], they were 2332ms2 for novice sympathectomy skiers, 4397ms² for normotonic skiers and 4973ms² for vagotonic skiers; according to [16], for male contractors, they amounted to 2,463ms², for Neurosoft employees (non-athletes) -1966ms², for track and field athletes-4144ms², for parachutists-3730ms², for football players-3510ms², for 16-year-old hockey players-4746 ms². So, K.D. has a median ortho-TR much lower than that of ESRT and YSRT and lower than that of representatives of other sports, and almost the same as that of non-athletes. These data indirectly indicate that after a 7-month absence of training, the synthesis of NN-ACh almost completely stops.

The change in the medians of the delta, i.e. the difference between the medians of the corresponding indicators of clino-HRV and ortho-HRV in the elite skier K.D. during the 7-month absence of training

Of the 15 HRV indicators that we analysed, data on the median’s delta-АPLF/АPHF, delta-pNN50% and delta-SI are of particular interest (Figure 1 & 2), which are known to reflect the activity of SD of ANS. In particular, these data indicate that in the absence of training, the synthesis of NN-Ach by cardiomyocytes decreases; this reduces the inhibitory effect of NN-Achn the activity of SD of ANS, which, as our unpublished data show, is characteristic of an active elite skier. Therefore, at K.D. when implementing the Prevel reflex (i.e., when implementing active orthostasis), the increase activity of SD of ANS in the absence of training is more pronounced than in the presence of training. So, with respect to the median of delta- АPLF/АPHF shows (Figure 1) that K.D. had in June 2019 (the first point of comparison) plus 8.2conl. units, in June 2020 (the second point of comparison)-plus 13conl. units and in the absence of loads, including in April, June, August and October 2024, it was respectively plus 17.8conl. units. With respect to the median of delta-pNN50%, it is shown (Figure 2) that in the presence of training loads at K.D. in June 2019, it was minus 83%, in June 2020-minus 88% and in the absence of loads, including in April, June, August and October 2024, it was minus 96%, minus 97%, minus 97% and minus 97%, respectively.

With respect to the median of delta-SI, it is shown (Figure 2) that in the presence of training loads at K.D. in June 2019 it was plus 38conl. units, plus 20 units in June 2020, and in the absence of loads, including in April, June, August and October 2024, it was respectively plus 44, plus 77, plus 68 and plus 97.3conl. units,

To a certain extent, data on the delta-APHF median also indicate a decrease in the synthesis of NN-Ach in October 2024 at K.D. As you know, APHF reflects the effect of PD of ANS on the activity of the heart. It was found (Figure 1) that in June 2019, the median of clino-APHF decreased by 91% during the transition to orthostasis, i.e. the delta was minus 91%$ in June 2020 it decreased by 93% and in the absence of loads, including in April, June, August and October 2024, it decreased by 95%, 97%, 96% and 97%, respectively, which was statistically significantly higher than in the presence of loads (p<0.05). These differences are also likely a consequence of the stronger effect of SD of ANS on cardiac activity in conditions of active orthostasis, since the production of NN-ACh is reduced.

Analysis of the dynamics of the indicators of clino-HRV, ortho-HRV and delta-HRV in the process of regression of sports vagotonia in an elite skier K.D.

An analysis of the dynamics of the medians of each of the 15 indicators of clino-HRV, ortho-HRV and delta-HRV during the 7 months of absence of training loads in K.D. (Figure 1 & 2) indicates the heterogeneity of their changes. In particular, in April, i.e. one month after the cessation of training, the medians of clino-and ortho-TP, clino-and ortho-АPHF, ortho-АPVLF, clino АPLF, ortho-- HF%, clino-and ortho-RRNN, ortho-RMSSD significantly decrease and the medians of ortho-АPLF/АPHF, deltaАsPLF/АPHF, clino-and ortho HR significantly increase. In June, i.e. three months after the cessation of training, there was a statistically significant decrease in the medians ortho-АPLF, ortho-SDNN, ortho-MxDMn and an increase in the median ortho-SI. In August, i.e. five months after the cessation of training, there was a decrease in the median clino- -RMSSD, clino--SDNN, clino-MxDMn and a significant increase in the median clino-SI. In October, i.e. seven months after the cessation of training, an increase in the median of clino-APLF/APHF was noted. At the same time, most HRV indicators reach a plateau in August and October. In general, an analysis of the dynamics of the median HRV indicators in an elite athlete K.D. allows us to conclude that the first signs of regression of sports vagotonia appear a month after the cessation of endurance training. Regression analysis of the dynamics of clino-HRV and ortho-HRV indices occurring during the 7-month cessation of training. It is established (Table 2) that in April 2024, i.e. in the first month of the non-training period, as this interval increases in K.D. there is a progressive decrease in the medians of clino-APHF, clino-RRNN, clino-pNN50% and clino- RMSSD, and an increase in the median of clino-HR (the Pearson coefficients of these indicators are statically significant).

Table 2:

Notes: 1) Statistically significant values of the Pearson linear regression coefficient are indicated in bold and with a * sign. The interpretation of HRV indicators is described in the section “Research methodology”.

However, in the interval “April-October”, the linear dependence of the medians of these indicators on the duration of the nontraining period is not revealed, since these medians reach a plateau after April. At the same time, the “April-October” is characterized by a gradual decrease in the median clino-HF% and clino-VLF% as the training period increases. With regard to the medians of ortho-HRV, it is shown that in April 2024, in K.D. with disabilities, as the nontraining period increases, the median of ortho-RRNN decreases and the median ortho HR increases and in the interval “April-October” these two indicators maintain the trend noted for April; In addition, in the interval “April-October”, the median of АPLF/АPHF increases as the non- training period increases. All this indicates that the regression of vagotonia occurs non-linearly. and multi-step. Table 2 values of the Pearson coefficient, reflecting the dependence of the medians of clino-HRV and ortho-HRV on the duration of absence of training loads, including in the first month (April) and for seven months (April -October).

The issue of the impact of stopping training by elite athletes (cyclists, marathon runners, swimmers) is actively discussed in the literature. In particular, there are several review papers on this issue [23-26], which analyse data obtained mainly in the 80s and 90s. According to [23,26], a break in elite athletes’ training may or may not be planned (for example, due to injury or illness), short-term or prolonged. This period has received various names, including the period of detoxification, or the period of maladjustment, or the regression of endurance, or the period of decondition. This period may occur with partial or complete cessation of exertion and from a psychological point of view, athletes may have different attitudes to the fact of forced cessation of exertion, which depends on the goals of sports and the presence of a formed dependence on exertion [27-29]. As a rule, the study of the effect of stopping exercise on the athlete’s body affects the first 15 weeks, while in the first week a marked change in a number of indicators reflecting a decrease in endurance is revealed [23,26]. The most detailed process of detraining elite athletes who train endurance is discussed in [23] In particular, it is reported that a complete cessation of training causes a rapid decrease in Maximum Oxygen Consumption (MOC), which, however, remains higher than that of non-athletes. For example, according to [29], a 3-8-week interruption of training in highly trained athletes reduces MOC by 20% And according to [30], with an 84-day cessation of training, MOC decreases by 7% on the 21^st day of this period, by 16% on the 56th day, after which it stabilizes at this level, which is 17.3% higher than that of non-athletes.

In addition to a decrease in MOC, the volume of circulating blood and blood plasma decreases by 5-12% [23,31] and systolic blood volume decreases (by 12-20%) when performing a submaximal test load [23,31].

In response to the testing load of submaximal power, the heart rate increases, but the minute volume of blood decrease and maximum ventilation of the lungs, or MVL [23]. Many authors have noted a decrease in the mass of the left ventricle of the heart, which is especially pronounced in the first 3 weeks of the non-workout period, reaching the level of non-athletes; it has been shown that this decrease is greater the longer the period of absence of training [23,26,32,33]. In addition, the cessation of training is accompanied by an increase (by 8%) total peripheral resistance, which remains elevated for 9-12 weeks and causes an increase in blood pressure [23,29]. During, this period, endurance decreases, judging by a decrease in training time to exhaustion and a decrease in athletic performance [23]. It has been established that significant metabolic changes occur already in the first weeks of stopping training, in particular, judging by an increase in the respiratory coefficient, the intake of carbohydrates for ATP resynthesis increases and the intake of lipids decreases [23], insulin sensitivity decreases to the level typical for non-athletes [23], the lactate threshold decreases, which manifests itself in a higher increase in lactate in response to testing load [23] and the glycogen content in skeletal muscles decreases [23]. Already in the first weeks, a negative mood is formed in athletes, especially if they have formed a dependence on training, which is manifested by depression, confusion, anger, fatigue, and decreased mood [28].

At the same time, there is no information about the nature of changes in the values of Heart Rate Variability (HRV) during the period of cessation of training We have not found any elite athletes who train for endurance in the literature available to us, including in the Medline system. Therefore, our data on the dynamics of the values of heart rate variability, which were recorded in the conditions of clinostats (clino-HRV) and active orthostasis (ortho- HRV) in an elite skier, K.D., we consider as new data, which to a certain extent agree with the data of the authors cited above [23,26]. Our study shows that a sudden decrease in training loads aimed at developing endurance, but while maintaining everyday motor loads, in an elite skier K.D judging by the change in the medians of clino-HRV and ortho-HRV, significantly changes the process of regulation of cardiac activity, and that probably reflects the literature data presented above [23-33]. In particular, the effect on the activity of the heart is reduced not only by the SD of ANS but also especially by the PD of ANS. The latter is probably due to a decrease in synthesis of NN-Ach. The decrease activity of PD is indicated by the fact that stopping training is accompanied by an increase in activation of SD during the implementation of an active orthostatic test (Prevel reflex). After 7 months of the nontraining process, there is a complete loss of vagotonia, which is characteristic of an elite skier, since according to many indicators of clino-HRV and ortho-HRV in October 2024, the former elite ski racer, athlete K.D. is almost indistinguishable from non-athletes. This means that the loss of vagotonia, i.e. its regression occurs much faster than the formation of vagotonia. We are aware that the case we are describing is an isolated one. Therefore, we do not exclude that the regression of vagotonia may occur faster or, conversely, slower for other elite skiers. We believe that after our work, observations will appear regarding the dynamics of HRV values during the sudden suspension of training of other elite skiers, as well as marathon athletes and elite representatives of other sports requiring the development of aerobic endurance and the pattern we have identified will be confirmed, along with clarifying the rate of vagotonia regression.

In the course of our research, based only on the dynamics of the median indicators of clino-and ortho-HRV, we paid great attention to the question of whether the synthesis of NN-AСh persists with vagotonia regression and, if so, to what extent? Of course, at present there is no direct and irrefutable evidence that certain specific HRV indicators reflect the synthesis of NN-ACh. Therefore, our assumption that during the regression of sports vagotonia, the synthesis of NN-ACh gradually decreases, but even at the end of the 7-month non-exercise period it is still partially preserved, is based only on a comparison of the values of the medians of clino-HRV and ortho-HRV, and not on direct data on the synthesis of NH-ACh. Therefore, further study of this issue is required in order to get a clear answer to it.

Regarding the nature of the regression of sports vagotonia in this article, we can only make some assumptions based on the idea of the process of adaptation to prolonged aerobic exercise of relatively high intensity, as a result of which sports vagotonia is formed [23,26,34-36]. On the one hand, it is an increase in the contractile activity of the heart, an increase in the effectiveness of beta1-adrenergic receptor activation, an increase in the synthesis of contractile proteins of the heart, an increase in mitochondrial biogenesis, an increase in coronary blood flow during muscle activity, an increase in the possibilities of external respiration and an increase in NOC as well as the formation of an anti-apoptotic, anti-inflammatory and antioxidant systems of the eart, a component of which is vagal ACh and probably NN-Ach. Therefore, during endurance training, the activity of SD ANS and PD ANS increases and, as we believe, the synthesis of NN-ACh increases. And the cessation of endurance training actually reduces the damaging effects on the heart, reduces the need for high activity of SD ANS, PD ANS, reduces the need for the synthesis of NN-ACh, the need for high activity of mitochondria, protein synthesis, the need for the formation of an anti-apoptotic, anti-inflammatory and antioxidant system of the heart, of which NN-ACh is a component.

Therefore, in conditions of acute cessation of training loads, the activity of SD and PD of ANS, as well as the intensity of NNACh synthesis decrease much faster than the formation of sports vagotonia. What mechanisms are involved in the regression of sports vagotonia? The answer to this question requires research. The importance of such studies is important for a deeper understanding of the mechanisms of adaptation of the human body to perform prolonged aerobic exercise of relatively high intensity. in particular, to understand the mechanisms of the formation of sports vagotonia. Of course, there is probably a big difference in how the regression of sports vagotonia proceeds in the case of a systematic gradual decrease in the volume of training loads that were used to increase endurance, and how the regression of vagotonia proceeds with an abrupt, sudden cessation of training loads. which in itself is stressful and a kind of physical inactivity. As is known, with true acute (sudden) physical inactivity, i.e., with complete disuse of skeletal muscles, special proteins that cause muscle fibre atrophy, i.e., atrogenic proteins, are activated and ROS production increases [37,38], the intensity of mitochondrial biogenesis decreases, the intensity of mitophagy, the intensity of mitochondrial fusion, the ability to synthesize ATP and many proteins, decreases ribosome activity, but increased apoptosis of myofibrils [38]. All these changes are based on a rapid (even within one day) decrease in the expression and activity of PGC-1a and other proteins regulating mitochondrial biogenesis, including such as NRF-1, NRF-2, ERR-α TFAM, as well as an increase in the expression of atrophy proteins [38]. In case of physical inactivity and when skeletal muscles are not used, Ca²⁺ homeostasis is disrupted, which is expressed in excessive leakage of Ca²⁺ into the cytosol and in overloading of mitochondria with Ca²⁺ ions. which induces apoptosis of muscle cells [38].

It is possible that these processes could also occur in an elite skier K.D. during a sudden cessation of training, which contributes to a rapid regression of vagotonia. There may be other factors that accelerated the regression of vagotonia in K.D. But, undoubtedly, among them, probably the leading place belongs to stress caused by the unplanned cessation of training loads, which the athlete K.D. continuously performed for 21 years, starting at the age of 10. In this work we did not analyse the influence of all these factors, as well as changes in physical performance, МОС, changes in the size of the left ventricle of the heart and other indicators important for endurance athletes, which may be partially the subject of further research. At the same time, our data demonstrate that regular physical training over a long period of time is necessary to achieve high results in cross-country skiing and consequently, to form athletic vagotonia, i.e., to have high activity of SD ANS, PD ANS and synthesis of NN-ACh by cardiomyocytes. For example, K.D., having started regular training at the age of 10, became a master of sports only at the age of 19.

On the other hand, our data show that the absence of training loads for even one month reduces the activity of SD ANS, PD ANS and probably the intensity of NN-ACh synthesis. This proves that the success of endurance development is determined by the consistency of the training process. From these positions, it can be argued that physical inactivity, which is characteristic of the majority of the population (non-athletes), is one of the leading causes of the development of diseases of the cardiovascular system in humans, since in this case the level of NN-ACh synthesis in the heart is so low that it does not protect the heart from stresses arising in everyday life and/or in production. In general, it can be assumed that interval cardiography as a safe research method) can be widely used in monitoring (medical examination) of the health of the adult population. Its use in sports medicine is especially important, including when accompanying the training process of ski racers and representatives of other endurance sports.

A. HRV registration in clinostats conditions revealed that after 7 months from the moment of forced cessation of training loads, the medians of 10 indicators of clino-HRV (TP, АPHF,, HF%, APVLF, APLF, RRNN, pNN50%, RMSSD, SDNN, MxDMn) statistically significantly decrease to the level typical for nonathletes and the medians of 3 indicators (VLF%, HR, SI) are increasing, and only the medians of 2 indicators (LF%, APLF/ APHF) are not changing. HRV registration in conditions of active orthostasis showed that during the same period, 11 indicators of ortho-HRV decreased to the level typical for nonathletes (TP, APHF, HF%, APVLF, VLF%, APLF, RRNN, pNN50%, RMSSD, SDNN and MxDMn) and the medians of 4 indicators (LF%, APLF/APHF, HR and SI) increase.
B. Changes in clino-HRV and ortho-HRV indices are characterized by heterochrony. The first statistically significant changes are observed a month after the cessation of training (i.e. in April 2024)-this is a decrease in the medians of clino-and ortho-TP, clino-and ortho-APMHF, ortho-PVLF, clino-APLF, ortho-HF%, clino-and ortho-RRNN, ortho-RMSSD, as well as the growth of medians ortho-and delta-APLF/APHF, clino-and ortho-HR. Three months after the end of training (in June 2024), the medians ortho- АPLF, ortho-SDNN, ortho-MxDMn decrease and the median ortho-SI increases. After 5 months (in August 2024), medians of clino-RMSSD, clino-SDNN, and clino- MxDMn decrease, and the median of clino-SI increases, and after 7 months (in October 2024), the median of clino-APLF/ APHF increases. At the same time, most indicators of HRV reach a plateau after 5 months (in August 2024) or 7 months (in October 2024) after the cessation of training loads.
C. The cessation of training loads aimed at developing endurance is accompanied by a decrease in activity of SD od ANS and especially a decrease of PD of ANS activity, including, probably, a decrease in the synthesis of NN-ACh, but the presence of which, even after 7 months of cessation of training, is still present in K.D. judging by the medians of such indicators as ortho-VLF%, ortho-APLF, clino-LF%, clino-and ortho-APLF/ APHF, clino-and ortho-RRNN, clino-and ortho-HR, and ortho- SI.
D. A decrease activity of PD ANS, including, probably, a decrease in the synthesis of NN-ACh, is accompanied by a more pronounced increase in the activity of CD ANS during the transition from clinostats to active orthostasis, as indicated by an increase median of delta-APHF, delta-APLF/APHF, deltapNN50 and delta SI.
E. Long-term aerobic training loads are required for the formation of sports vagotonia, but a relatively short period of time is sufficient for its regression, judging by the data of the elite skier K.D., no more than 7 months in the complete absence of training loads.