Cardiorespiratory Coordination during Physical Exercise Depends on the Zone of Its Intensity in Young Athletes

It has previously been shown that the assessment of cardio-respiratory coordination (CRC) using principal component analysis (PCA) when performing exercise to exhaustion is sensitive to the physical condition of a person. However, the functional state of the body changes depending on the intensity of physical activity and adaptation to the load, while the CRC can also change. Among cyclic sports, swimming is distinguished by increased work of respiratory muscles in water and a special breathing pattern synchronized with limb movements. This type of breathing can change the CRC. The aim of this study was to investigate the dynamics of CRC at rest, during physical exertion up to the ventilatory threshold (VT) and from the VT to the respiratory compensation point (RCP), as well as during a recovery load of 25 W in swimmers and skiers. The study involved 17 swimmers and 17 skiers aged 13–16 years with an adult sports category and at least 3 years of experience in sports. A gradually increasing workload was performed on a bicycle ergometer until the pulse corresponded to 85% of the intensity according to Karvonen. CRC was assessed by PCA over 10 time series averaged heart rate (HR), respiratory, and gas exchange parameters for each adolescent. The percentage of total variance in cardiorespiratory parameters explained by principal component 1 (PC1) was considered the CRC value. The dynamics of the CRC in swimmers and skiers with increasing bicycle ergometric load depends on the intensity of the load (F (3, 90) = 51.8; p = 0.000) and does not depend on the type of sport (F (1, 30)=1.71; p = 0.20), sex (F (1, 30) = 0.01; p = 0.94), or the interaction of factors (for all interactions F (3, 90) < 0.9; p > 0.44). The minimum coordination between heart rate, minute respiratory volume, FeO2, and FeCO2 was found at rest (55%), and the maximum was found at the aerobic (up to VT) stage of increasing bicycle ergometric load (80%, p < 0.001 compared to rest). Further, the CRC decreased at the stage from VT to RCP (74%) due to FeCO2, which is not correlated with the other variables (p < 0.01), and at the stage of active recovery (72%), due to FeO2 (p < 0.01). Thus, CRC depends on the exercise intensity zone. Adaptation to swimming and sex do not influence CRC values at different stages of exercise intensity.