Dependence of Clinostatic and Orthostatic Cardiointervalography Parameters on the Duration (Volume) of Training and Competition Loads of Aerobic and Anaerobic Nature of an Elite Racer-Skier

Elite cross-country skier K.D., a member of the men’s national team of the Republic of Tatarstan, Master of Sports of Russia, had his heart rate variability (HRV) recorded sequentially (for 5 min) almost daily during two ski seasons (2018–2019 and 2019–2020) during the preparatory, competitive, and transition periods under conditions of clinostasis and then under conditions of active orthostasis. The values of eight spectral and six temporal indicators of clino-HRV and ortho-HRV were compared (taking into account the five “working pulse” zones) with the total duration of the load (TDL1–5), as well as with the duration of aerobic (DL1–3) or anaerobic (DL4–5) loads. It was shown that, during endurance training, the influence of the sympathetic division (SD) of the autonomic nervous system (ANS) on the heart increases, and especially the influence of the parasympathetic division (PD) of the autonomic nervous system (ANS), including owing to the appearance of non-neuronal acetylcholine (NN-ACh) synthesis in cardiomyocytes as a component of the anti-apoptotic, antioxidant, and anti-inflammatory system. It was established that the nature of the statistically significant dependence of the medians (11 out of 14) of the HRV indicators on the total duration of the load (TDL1–5), as well as on the duration of aerobic (DL1–3) or anaerobic (DL4–5) loads in elite cross-country skier K.D., depends on the conditions under which the HRV is recorded—in clinostasis or in active orthostasis. The change in the nature of the dependence of the HRV parameters under active orthostasis is explained by the presence of non-neuronal acetylcholine (NN-ACh), the synthesis of which by cardiomyocytes occurs during endurance training. On the basis of the nature of the change in the dependence of the medians of the HRV parameters on the duration of training or competitive loads observed during active orthostasis (in comparison with clinostasis), nine criteria for the presence of NN-ACh synthesis in the heart of an athlete training for endurance are proposed.