Background: The maximum depth achievable in freediving is limited by a combination of pulmonary,
cardiovascular and technical factors. As the lungs, being a compressible reservoir of respiratory volume, are
directly subject to the increase in hydrostatic pressure, pulmonary function testing is considered to play a central
role in assessing an individual’s depth capacity and the risk of injury (‘lung squeeze’).

Objective: This review compares common pulmonary function tests in terms of their predictive value for
maximum freediving depth and compares the results with those from freedivers and SCUBA divers. The aim was
to analyse functional, structural and exercise-physiological differences between 30 AIDA competitive freedivers
and 30 experienced SCUBA divers.

Methodology: A literature review was conducted in PubMed, Frontiers, Springer Link and other databases on the
physiological determinants of apnoe diving depth. In a cross-sectional analysis, various medical measurement
methods, including spirometry, body plethysmography and DLCO (diffusion capacity) measurement, were
employed and compared with the average diving depth achieved.

Results: The ratio of residual volume to total lung capacity (RV/TLC) has a theoretical, mathematical
relationship with the depth limit, whilst spirometry parameters were also found to be useful, offering a higher
probability of prediction. Freedivers exhibited significantly higher total lung capacities (TLC) and functional
residual capacities (FRC) than SCUBA divers. DLCO was significantly elevated in freedivers, suggesting an
increased alveolar-capillary exchange surface area.

Diffusion capacity measurement provided the highest predictive value for the average dive depth achieved
by 30 AIDA freedivers.

Conclusion: As a single test, diffusion capacity measurement allows for a reliable individual prediction of
maximum apnoe diving depth.