Exposure to a combination of heat and hyperoxia during cycling at submaximal intensity does not alter thermoregulatory responses

In this study, we tested the hypothesis that breathing hyperoxic air (F(in)O(2) = 0.40) while exercising in a hot environment exerts negative effects on the total tissue level of haemoglobin concentration (tHb); core (T(core)) and skin (T(skin)) temperatures; muscle activity; heart rate; blood concentration of lactate; pH; partial pressure of oxygen (P(a)O(2)) and carbon dioxide; arterial oxygen saturation (S(a)O(2)); and perceptual responses. Ten well-trained male athletes cycled at submaximal intensity at 21°C or 33°C in randomized order: first for 20 min while breathing normal air (F(in)O(2) = 0.21) and then 10 min with F(in)O(2) = 0.40 (HOX). At both temperatures, S(a)O(2) and P(a)O(2), but not tHb, were increased by HOX. Tskin and perception of exertion and thermal discomfort were higher at 33°C than 21°C (p < 0.01), but independent of F(in)O(2). T(core) and muscle activity were the same under all conditions (p > 0.07). Blood lactate and heart rate were higher at 33°C than 21°C. In conclusion, during 30 min of submaximal cycling at 21°C or 33°C, T(core), T(skin) and T(body), tHb, muscle activity and ratings of perceived exertion and thermal discomfort were the same under normoxic and hyperoxic conditions. Accordingly, breathing hyperoxic air (F(in)O(2) = 0.40) did not affect thermoregulation under these conditions.