Examining placebo effects after a 3-week repeated-sprint training program under hypoxic conditions in recreationally trained subjects: a randomized controlled trial

Repeated-sprint training in hypoxia (RSH) has been suggested to significantly enhance anaerobic performance. However, the widespread belief in the benefits of altitude training raises questions about potential placebo effect. The aim of this study was thus to investigate the physiological and placebo effects of normobaric hypoxia combined with repeated-sprint training on performance. Twenty-nine moderately trained participants were randomly assigned to normoxia (repeated-sprint in normoxia (RSN)), placebo (repeated-sprint in normoxia with placebo setup (RSN-P)), or hypoxia (RSH) groups. Participants in RSN-P group were led to believe they were training at simulated altitude (between 2500 and 3500 m), while participants in the RSN and RSH groups knew they were training at sea level and at altitude, respectively. Repeated-sprint training involved six cycling sessions over 3 weeks, consisting of three sets of 8 × 6 s sprint with 24 s of recovery. There was no difference in the estimation of the altitude level to which participants from the RSN-P and RSH groups thought they had been exposed. There was a main significant effect of training on mean power output during Wingate (+7.9%; <i>p</i> < 0.001; <i>ηp²</i> = 0.47) and repeated-sprint ability tests (+7.7%; <i>p</i> < 0.001; <i>ηp²</i> = 0.55). However, contrary to our hypotheses, the enhancement among the three groups did not differ. The lack of greater improvement in the RSH group compared to the other groups raises questions about the added value of hypoxia in these conditions. In conclusion, neither real nor perceived hypoxia enhanced training adaptations following repeated-sprint sessions.