Normobaric hypoxia reduces VO2 at different intensities in highly trained runners

Introduction: We sought to determine the effect of low and moderate normobaric hypoxia on oxygen consumption and anaerobic contribution during interval running at different exercise intensities. Methods: Eight runners (age, 25 +/- 7 yr, V[spacing dot above]O2max: 72.1 +/- 5.6 mL[middle dot]kg-1[middle dot]min-1) completed three separate interval sessions at threshold (4 x 5 min, 2-min recovery), V[spacing dot above]O2max (8 x 90 s, 90-s recovery), and race pace (10 x 45 s, 1 min 45 s recovery) in each of; normoxia (elevation: 580 m, FiO2: 0.21), low (1400 m, 0.195) or moderate (2100 m, 0.18) normobaric hypoxia. The absolute running speed for each intensity was kept the same at each altitude to evaluate the effect of FiO2 on physiological responses. Expired gas was collected throughout each session, with total V[spacing dot above]O2 and accumulated oxygen deficit calculated. Data were compared using repeated-measures ANOVA. Results: There were significant differences between training sessions for peak and total V[spacing dot above]O2, and anaerobic contribution (P < 0.001, P = 0.01 respectively), with race pace sessions eliciting the lowest and highest responses respectively. Compared to 580 m, total V[spacing dot above]O2 at 2100 m was significantly lower (P < 0.05), and anaerobic contribution significantly higher (P < 0.05) during both threshold and V[spacing dot above]O2max sessions. No significant differences were observed between altitudes for race pace sessions. Conclusions: To maintain oxygen flux, completing acute exercise at threshold and V[spacing dot above]O2max intensity at 1400 m simulated altitude appears more beneficial compared with 2100 m. However, remaining at moderate altitude is a suitable when increasing the anaerobic contribution to exercise is a targeted response to training.