Impact of moderate-intensity aerobic exercise in combined hypoxic and hot conditions on endothelial function

There is no study that has investigated the impact of exercise in a combined hypoxic and hot environment on endothelial function. Therefore, we tested whether aerobic exercise in a combined hypoxic and hot conditions induces further enhancement of endothelial function. Twelve healthy males cycled at a constant workload (50% of their maximal oxygen uptake under normoxic/thermoneutral conditions) for 30 min in four different environments: exercise under normoxic condition (NOR: fraction of inspiratory oxygen or FiO₂ = 20.9%, 20°C), exercise under hypoxic condition (HYP: FiO₂ = 14.5%, 20°C), exercise under hot condition (HOT: FiO₂ = 20.9%, 30°C), and exercise under combined hypoxia and hot conditions (HH: FiO₂ = 14.5%, 30°C). Before, during, and after exercise, cardiovascular variables (e.g., heart rate, blood flow, and shear rate), blood variables, and endothelial function evaluated by flow-mediated dilation (FMD) were assessed. Heart rates were significantly higher throughout the HH trial's experimental period than the other trials (p < 0.05). However, in the HH trial, brachial artery blood flow and shear rate did not differ from those in other trials after exercise. Plasma catecholamines (epinephrine, norepinephrine, and dopamine) elevations in response to exercise were significantly higher in the HH trial than in the other three trials (p < 0.05). No considerable differences were observed in FMD responses among trials before and after the exercise. In conclusion, aerobic exercise in a combined hot and hypoxic environment further activated sympathetic nervous activity but did not considerably enhance blood flow, shear rate, or endothelial function.