Cardiorespiratory Coordination in Acute Hypoxia in Runners

The study was aimed at determining cardiorespiratory coordination under the influence of acute hypoxia in athletes with different levels of sports qualifications. Eighteen runners aged 17 to 25 were exposed to acute (10% O2) hypoxia for 10 min. Respiration, gas exchange, and heart rate were measured during normoxia and hypoxia. The principal component (PC) analysis was used to assess cardiorespiratory coordination; the stability of PCs under the influence of hypoxia was evaluated by the Tucker’s Congruence Coefficient. The analysis was performed on a time series of 10 min of normoxia and hypoxia with the inclusion of heart rate, minute ventilation, the expired fraction of O2 and CO2. According to the level of qualification, athletes were divided into two groups: highly trained (HT, no less than category I, n = 9) and medium-trained (MT, category II, n = 9). Under normoxia, cardiorespiratory coordination in athletes of both groups was higher than in normobaric hypoxia (p = 0.001): during normoxia, the model included one PC from coordinated variables according to the Kaiser criterion in 44% of the athletes; during hypoxia, the model consisted of two PCs in 100% of the athletes. During hypoxia, the percentage of total variance explained by PC2 increased significantly (p < 0.001), regardless of the level of qualification. In hypoxia, there was a change in the variable contributions to PC1 and PC2, more pronounced in the MT group: the contribution of heart rate to PC1 increased, and the expired fraction of CO2 decreased (p < 0.001). The congruence coefficient of the first PC between normoxia and hypoxia in the HT group showed a high level of similarity (median = 0.88; 25/75% = 0.84/0.93) and was significantly (p < 0.05) higher than in MT (0.82; 0.46/0.94). Thus, highly qualified athletes have the higher cardio-respiratory stability under hypoxic exposure. This can be an additional predictive sign of good athletic performance.