Background: Intermittent hypoxic recovery has been proposed as a strategy to increase physiological demand during repeated high-intensity exercise while preserving external load. Its effects on metabolism remain poorly understood. Aim: To investigate the effects of acute inter-effort normobaric hypoxic recovery on metabolomic responses after repeated maximal swimming efforts. Methods: Fourteen competitive swimmers with regional to national-level experience completed two randomized crossover sessions separated by 48 h, each consisting of 10 × 50-m maximal preferred-stroke efforts with 4-min passive recovery under normoxia (FiO* = 20.9%) or hypoxia (FiO* = 13.3%) delivered through a mask. Venous blood samples were collected before and after each session for plasma metabolomic profiling. Fifty-seven plasma metabolites were included in the analysis. Principal component analysis (PCA) was used to explore global metabolic responses. Delta values (post minus pre) were calculated for each metabolite to isolate condition-specific effects. Linear mixed models were applied to test condition effects, with participant included as a random factor. Hypoxic dose was estimated from oxygen saturation data recorded during recovery intervals using integrated desaturation area below 98%. Results: PCA showed a clear pre- to post-exercise separation, indicating that exercise was the dominant source of global metabolic variance. PCA of delta values did not reveal clear separation between hypoxia and normoxia. Among metabolites contributing most strongly to multivariate structure, alanine showed a significant condition effect, with greater increases under hypoxia (p = 0.047; d = 0.51) and moderate associations with integrated hypoxic dose (r = 0.37; p = 0.20) and fatigue index (r = 0.35). Inosine and lactate showed smaller non-significant effects. Conclusions: Acute inter-effort hypoxic recovery selectively increased alanine response without inducing global metabolomic separation, suggesting greater metabolic stress during repeated swimming efforts.
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