Inter-Effort Recovery Hypoxia Increases Peak Oxygen Consumption without Hematological Changes

Intermittent hypoxia combined with physical training may enhance performance and health parameters but can impair session quality, limiting adaptations. To address these drawbacks, inter-effort recovery hypoxia has been proposed. This study investigated the effects of a 5-week inter-effort recovery hypoxia protocol followed by a 1-week tapering period in recreational runners. Twenty-four men were allocated to an inter-effort recovery hypoxia group (n = 11) or a normoxia group (n = 13) and assessed for body composition, hematological profile, running economy, maximum velocity, and peak oxygen uptake before training (W0), after training (W6), and after tapering (W8). Training consisted of 3 weekly sessions for 5 weeks: a 5-minute warm-up at 60% of maximum velocity, ten 1-minute effort at 120% (wk 1-3) or 130% (wk 4 and 5) of maximum velocity with 2-minute passive recovery, and 5-minute cool-down at 60% of maximum velocity. The inter-effort recovery hypoxia group inhaled hypoxic air (fraction of inspired oxygen=0.136) during warm-up, recovery bouts, and cool-down. Outcomes were analyzed using generalized linear mixed models. Peak oxygen uptake increased in the inter-effort recovery hypoxia group at W6 (+7%) and W8 (+10%), while the normoxia group improved at W8 (+7%), without group differences; running economy improved in the normoxia group at W8 (+10%). No significant changes occurred in erythropoietin, erythrocytes, hemoglobin, reticulocytes, or body composition. The 5-week inter-effort recovery hypoxia protocol enhanced peak oxygen uptake without hematological changes, indicating a feasible and non-erythropoietic strategy for improving aerobic fitness.