Effects of Combined Heat and Hypoxic Training on the Physiological Responses During Submaximal Interval Exercise in Untrained Men.

Background and Objectives: Aerobic submaximal interval training performed under hypoxic and elevated temperature conditions may induce significant alterations in physiological responses. Understanding these effects may contribute to optimizing training programs for athletes and individuals exposed to extreme environmental conditions. The aim of this study was to investigate the impact of combined heat and hypoxia training on physiological response and adaptation during submaximal interval training in untrained men. Methods: Eighty men aged 19-26 years, reporting moderate physical activity levels, were randomly assigned to one of five groups: normoxic thermoneutral training (NOR+21 °C), intermittent hypoxic training in normothermia (IHT+21 °C), normoxic training in heat (NOR+31 °C), intermittent hypoxic training in heat (IHT+31 °C), or a control group (CON). Training sessions were conducted three times per week over a four-week period (12 sessions in total). Somatic parameters and a graded exercise test were assessed before and after the intervention. On the first and last training sessions, selected physiological indices were recorded, including the Bedford scale, Borg Rating of Perceived Exertion (RPE), heart rate (HR), tympanic temperature (Ttym), and skin temperature (Tsk), hematocrit (Hct), and hemoglobin (Hb) and lactate concentration. Statistical analyses included descriptive statistics and analysis of variance (ANOVA) with Tukey's post hoc test (p < 0.05). Results: A statistically significant decrease in heart rate (p = 0.04) and exercise intensity expressed as a percentage of maximal heart rate (%HRmax) (p = 0.03) was observed in the IHT+21 °C group following the training intervention. Furthermore, a significant decrease in RPE was found in the IHT+21 °C (p = 0.04) and IHT+31 °C (p = 0.001) groups. A significant change in tympanic temperature was noted only in the IHT+21 °C group, where it increased post-intervention (p = 0.01). No significant changes in Hct and Hb were observed as a result of training. Conclusions: The combination of hypoxic and heat training did not yield the expected results, and no significant changes in the physiological response to submaximal aerobic training were observed in untrained men. In untrained young men, training under hypoxic and thermoneutral conditions leads to significant physiological adaptations, including reductions in heart rate and relative exercise intensity (%HRmax) after the intervention. Moreover, both hypoxia alone and hypoxia combined with heat were associated with a reduced perception of exertion following the training period.