Background: Hypoxic training is used in swimming to augment physiological stress and potentially improve sea-level performance. However, hematological, peripheral, or molecular responses do not necessarily translate into faster competitive swimming. Methods: This narrative review was developed from a scientific lecture on hypoxic training in swimming. The initial sources reflected the authors` accumulated reading, scientific experience, and previously selected literature. A complementary, non-exhaustive update through July 2026 was undertaken in major bibliographic databases to identify recent publications and refine the discussion. Swimmer-specific evidence was prioritized; studies from other sports were used only as indirect mechanistic or contextual support. Results: Live-high-train-high and live-high-train-low protocols frequently increased total hemoglobin mass or red-cell volume in swimmers, but performance benefits were inconsistent and depended on the protocol, individual response, training quality, and timing of assessment. Live-low-train-high findings were mixed, some land-based interventions in moderately trained swimmers reported favorable changes, whereas controlled swimming-specific protocols did not consistently demonstrate an additional benefit of hypoxia. Inter-effort recovery hypoxia (IEH) can increase hypoxemia and cardiovascular stress while preserving acute external work, but swimmer-specific evidence remains predominantly acute, based on small samples, or available only as conference abstracts. Chronic IEH studies have been conducted mainly in runners and do not establish efficacy in swimming. Conclusions: Hypoxia is not a universal ergogenic stimulus. Its application should be aligned with the intended adaptation, event demands, athlete level, iron availability, training-load management, technical quality, and the post-altitude assessment window. IEH introduces the timing of hypoxic exposure within a session as a relevant methodological variable, but it cannot yet be recommended as a proven means of improving competitive swimming performance.
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