Effects of normobaric hyperoxic recovery after exercise on subsequent performance: a systematic review and meta-analysis with secondary physiological outcomes.

backgroundNormobaric hyperoxic recovery has been proposed as a post-exercise strategy to improve subsequent exercise performance, but the overall performance evidence and the consistency of accompanying physiological recovery markers remain unclear. This systematic review and meta-analysis primarily evaluated the effect of normobaric hyperoxic recovery on subsequent performance, with selected physiological outcomes interpreted as secondary and exploratory evidence.

methodsWe systematically reviewed studies examining normobaric hyperoxic recovery after exercise. Performance was prespecified as the primary outcome. Peripheral oxygen saturation (SpO₂), heart rate (HR), and blood lactate (BLa) were treated as secondary outcomes. After full-text verification, 19 reports were retained, yielding 21 study entries for synthesis. Because many studies used crossover, repeated-measures, or within-subject designs and most did not report sufficient paired-variance information, the main quantitative syntheses used arm-level summary statistics and random-effects models with standardized mean differences (Hedges' g).

resultsThe primary performance analysis included 16 study entries and estimated a small-to-moderate effect in favor of normobaric hyperoxic recovery (SMD = 0.42, 95% CI 0.22 to 0.63; I² = 0%). This estimate was not materially altered in leave-one-out, trim-and-fill, fail-safe N, and prespecified structural sensitivity analyses. For secondary outcomes, 10 study entries contributed to the BLa analysis, which showed no clear pooled effect (SMD = 0.14, 95% CI -0.15 to 0.43; I² = 0%). Although funnel-plot asymmetry was detected for BLa, trim-and-fill did not materially alter the pooled estimate. HR results were based on 2 exploratory study entries and showed no clear pooled effect (SMD = 0.29, 95% CI -0.35 to 0.93; I² = 0%). SpO₂-related outcomes were highly heterogeneous (I² = 90.0%), and this inconsistency persisted after sensitivity analyses, supporting narrative rather than pooled inferential interpretation.

conclusionsNormobaric hyperoxic recovery was associated with a modest, directionally consistent effect in favor of subsequent performance. In contrast, the secondary physiological outcomes provided limited and inconsistent evidence. No clear pooled effect was observed for blood lactate, heart-rate findings were exploratory, and SpO₂ outcomes were too heterogeneous to support a stable pooled conclusion. Overall, the findings suggest a possible performance benefit of normobaric hyperoxic recovery, while physiological outcomes should be interpreted as descriptive and hypothesis-generating rather than as evidence of a consistent physiological recovery response.