Background: Breath-hold diving (BHD, also referred to as freediving) represents an extreme physiological challenge, requiring adaptations to rapid changes in blood gas levels and hydrostatic pressure. Despite advances in understanding human responses to BHD, knowledge gaps remain. With this state-of-the-art review, research trends and progression were tracked to inform future investigation directions.
Methods: A structured literature search was conducted in PubMed and Scopus (2005–2025), selecting peer-reviewed studies on physiological, biochemical, and biomechanical aspects of BHD. Thematic analysis identified eight major research areas: cardiovascular, pulmonary, and neurological systems, decompression stress, skeletal muscle and metabolism, training, long-term adaptations, and technological advancements.
Results: Cardiovascular adaptations involve autonomic regulation, bradycardia, and splenic contraction, but uncertainties remain regarding individual variability. Pulmonary responses include lung compression, gas exchange inefficiencies, and potential risks of lung barotrauma. Neurological effects include hypoxia-induced syncope, cerebral blood flow changes, and emerging evidence of neurovascular damage. Decompression stress, once considered negligible, is now recognized in elite and repetitive divers. Training enhances apnea performance through hematological and metabolic adaptations, though long-term effects are unclear. Telemonitoring advancements are promising for future improvement of divers’ safety.
Conclusions: Recent observations emphasize both adaptive and maladaptive aspects of BHD physiology. The synthesized research trends should aim at refining current achievements and identify what individual and environmental factors pose specific limits for human breath-hold performance underwater.
Supplementary Information: The online version contains supplementary material available at 10.1007/s00421-025-06093-6.
Keywords: Apnea; Breath-hold diving; Cardiovascular adaptations; Decompression stress; Diving physiology; Environmental physiology; Underwater.