The Effects of Repeated Thermal Stress on the Physiological Parameters of Young Physically Active Men Who Regularly Use the Sauna: A Multifactorial Assessment

The aim of this study was to determine the effects of thermal stress (TS) on changes in blood biochemical parameters and fluid electrolyte levels in young adult men with moderate and high levels of physical activity. Thirty men (22.67 ± 2.02 years) were exposed to four 12-min sauna sessions (temperature: 90–91 °C; relative humidity: 14–16%) with four 6-min cool-down breaks. The evaluated variables were anthropometric, physiological, and hematological characteristics. The mean values of HR(avg) (102.5 bpm) were within the easy effort range, whereas HR(peak) (143.3 bpm) values were within the very difficult effort range. A significant increase was noted in pO2 (p < 0.001), total cholesterol (p < 0.008), HDL (p < 0.006) and LDL cholesterol (p < 0.007). Significant decreases were observed in the SBP (by 9.7 mmHg), DBP (by 6.9 mmHg) (p < 0.001), pH (p < 0.001), aHCO(3)- (p < 0.005), sHCO3- (p < 0.003), BE (ecf) (p < 0.022), BE (B), ctCO(2) (for both p < 0.005), glucose (p < 0.001), and LA (p < 0.036). High 72-min TS did not induce significant changes in the physiological parameters of young and physically active men who regularly use the sauna, excluding significant loss of body mass. We can assume that relatively long sauna sessions do not disturb homeostasis and are safe for the health of properly prepared males.