Fifteen-second bouts of hyperoxia improve 5-minute time-trial performance in acute hypoxic conditions

Introduction Hyperoxia, e.g. administration of 100 % oxygen, is a wide spread tool to improve blood oxygenation (e.g. in emergency medicine) but is also applied in elite sports to improve training intensity or competition performance. The positive effects of continuous hyperoxia during aerobic high-intensity exercise has been shown repeatedly, however, the potential effects of intermittent doses are unclear. Out study aimed to test the effects of repeated bouts of hyperoxia, each lasting fifteen seconds, on maximal 5-minute cycling performance under acute hypoxic conditions. Methods 17 healthy and recreationally trained individuals (7 females, 10 males, age 27 ± 4 years) participated in this randomized placebo-controlled cross-over trial. The procedures included a graded cycle ergometer test until exhaustion and three maximal 5-minute cycling time trials (TT). The peak power output during the maximal cycle ergometer test provided the basis for the determination of the target power output for the TTs. The subsequent TTs were conducted in a normobaric hypoxic chamber at the Department of Sport Science of the University Innsbruck (590 m). TT1 took place in normoxia and served for habituation and reference. TT2 and TT3 were conducted in normobaric hypoxia (15.0 % inspiratory fraction of oxygen, corresponding to about 3200 m simulated altitude). During TT2 and TT3 the participants were breathing through a face mask during five 15-second periods (0:20 to 0:35; 1:20 to 1:35; etc.). The face mask was connected via a non-rebreathing T-valve to a 300-litre bag filled with 100 % oxygen (intermittent hyperoxia condition) or ambient hypoxic air (placebo condition). Heart rate was recorded continuously during the TTs. Ratings or perceived exertion were recorded after test termination and capillary blood samples were taken from the hyperaemic earlobe 2 minutes later to analyze blood lactate concentrations. Arterial oxygen saturation was measured via finger pulse oximeter during a 60-second period (ca. minutes 2:00 to 3:00). Thereby, one 15-second hyperoxic intervention bout during the test in the intermittent hyperoxia condition was included. Main outcome was the mean power output during the TT. Statistical significance level was set at p < 0.05. Results Mean power output was higher in the intermittent hyperoxia compared to the placebo condition (255.5 ± 49.6 W versus 247.4 ± 48.2 W, p = 0.001). Blood lactate concentration and ratings of perceived exertion were significantly lower in the intermittent hyperoxia compared to the placebo condition (10.2 ± 1.7 mmol/L versus 11.3 ± 2.5 mmol/L and 17.8 ± 1.4 versus 19.2 ± 1.1 respectively). However, heart rate values were unchanged between conditions (168.0 ± 8.6 bpm versus 169.4 ± 10.3 bpm, p = 0.332). Arterial oxygen saturation increased by the 15-second application of hyperoxia (82.9 ± 2.6 % to 92.4 ± 3.3 %, p < 0.001). Conclusion Repeated 15-second bouts of hyperoxia, applied during high-intensity exercise in hypoxia, are sufficient to increase power output. Future studies should focus on potential dose-response effects and the involved mechanisms.