Muscle Oxygenation during Repeated Cycling Sprints in a Combined Hot and Hypoxic Condition

The aim of the present study was to examine the effects of a combined hot and hypoxic environment on muscle oxygenation and performance during repeated cycling sprints. In a single-blind, counterbalanced, cross-over research design, 10 male athletes performed three sets of 3 x 10-s maximal pedaling interspersed with 40-s recovery between sprints under four different environments. Each condition consisted of a control (CON; 20 degrees C, 20.9% FiO (2) ), normobaric hypoxia (HYP; 20 degrees C, 14.5% FiO (2) ), hot (HOT; 35 degrees C, 20.9% FiO (2) ), and combined hot and normobaric hypoxia (HH; 35 degrees C, 14.5% FiO (2) ). Power output and vastus lateralis muscle oxygenation were measured. Peak power output was significantly higher in HOT (892 +/- 27 W) and HH (887 +/- 24 W) than in CON (866 +/- 25 W) and HYP (859 +/- 25 W) during the first set (p<0.05). The increase in total hemoglobin during recovery periods was larger in HH than in HYP (p<0.05), while change in tissue saturation index was smaller in HYP than in CON and HOT (p<0.05). The findings suggest that the combination of hot and hypoxia during repeated cycling sprints presented different characteristics for muscle metabolism and power output compared to temperature or altitude stressor alone.