This study aimed to compare selected hormonal responses to a single session of high intensity interval training performed with an increased fraction of inspired
oxygen (
hyperoxia) and under normoxic conditions. Twelve recreationally trained men (age 24 ± 3 years) performed two sessions of high intensity interval training on a cycle ergometer, in randomized order with
hyperoxia (4 L·min-1 with a flowrate of 94% O2) and normoxia. Each session consisted of 5 intervals of 3 minutes at 85% of the maximal power output, interspersed by 2 min at 40% of the maximal power output. Serum
cortisol,
prolactin and
vascular endothelial growth factor (
VEGF) were assessed both before and immediately after each high intensity interval training session. Statistically significant differences in
cortisol were found between hyperoxic and normoxic conditions (p = 0.011), with a significant increase in
hyperoxia (61.4 ± 73.2%, p = 0.013, ES = -1.03), but not in normoxia (-1.3 ± 33.5%, p > 0.05, ES = 0.1).
Prolactin increased similarly in both
hyperoxia (118.1 ± 145.1%, p = 0.019, ES = -0.99) and normoxia (62.14 ± 75.43%, p = 0.005, ES = -0.5).
VEGF was not statistically altered in either of the conditions. Our findings indicate that a single session of high intensity interval training in low-dose
hyperoxia significantly increased
cortisol concentrations in recreationally trained individuals compared to normoxia, while the difference was smaller in
prolactin and diminished in
VEGF concentrations.