Is the use of hyperoxia in sports effective, safe and ethical?

With considerable interest, we are following developments concerning the increasingly popular practice of breathing oxygen (O2)-enriched air (normobaric hyperoxia) in an attempt to improve both athletic performance and recovery, especially by elite endurance athletes (Hevoskuuri 2016). Administration of supplemental O2 is not prohibited by the World Anti-Doping Agency, and indeed, there is striking evidence that when administered at sea-level, hyperoxia (i.e., an inspired fraction of O2 (FiO2) greater than normoxic FiO2 >0.2095) improves power output by 2.4–16.5% during both maximal and submaximal cycling (Hogan et al., 1983; Plet et al., 1992; Knight et al., 1993, 1996; Walsh & Banister, 1995; Linossier et al., 2000; Peltonen et al., 2001; Prieur et al., 2002; Grataloup et al., 2005; Amann et al., 2006; Tucker et al., 2007; Lovering et al., 2008; Vogiatzis et al., 2008; Segizbaeva & Aleksandrova, 2009). Hyperoxia increases the arterial O2 pressure (PaO2), the saturation of hemoglobin (Hb) with O2 (SaO2), and the amount of oxygen dissolved in the plasma. Consequently, the arterial oxygen content (CaO2) is greater during hyperoxic breathing, implying that for a given cardiac output systemic O2 delivery, which has been shown to be a major determinant of VO2max (Saltin & Calbet, 2006) and endurance, is enhanced (Amann & Calbet, 2008). From a practical point of view, an athlete could benefit from hyperoxia in three different ways: