Background: Swimmers exhibit superior lung function compared to both other athletes and non-athletes. Whether this is attributable to genetic predisposition, the effects of swimming training, or a combination of both, remains unclear. Aim: To investigate how lung function develops in adolescent swimmers compared to controls and predicted values. Methods: This study has a longitudinal observational design and includes 33 competitive swimmers (21 female), training >2 times/week. At ages 12 and 15, the following assessments were performed: forced expiratory volume in the first second (FEV1) and forced vital capacity (FVC), measured by maximal flow volume curves. Diffusion capacity for carbon monoxide (DLCO) and alveolar volume (VA) measured by the single-breath technique; and total lung capacity (TLC) measured by whole-body plethysmography. An existing age-matched cohort of team ball sport athletes (7 female, 6 male) served as controls for FVC and FEV1. Independent T-tests are used for comparing swimmers and controls and paired sample T-tests with Bonferroni adjustments for assessing changes between 12 and 15 years, which is equivalent to testing the Group×Time interaction in a repeated-measures ANOVA given the two-timepoint design. Results: At age 12, groups were comparable in FVC (swimmers: 106±10.3% vs. controls: 105±9.2% predicted) and FEV* (102±10.8% vs. 104±10.9%). By age 15, swimmers showed significantly higher FVC than controls (110±11.7% vs. 101±7.7%, p=0.019). Within the swimmer group, FVC (106% to 110%, *4±6.4%, p=0.004), VA (104% to 108%, *4±10.6%, p=0.047), and TLC (105% to 113%, *5±9.6%, p=0.013) all increased significantly from age 12 to 15, while no significant changes were observed in controls or in other variables. Conclusions: Adolescent swimmers showed greater growth in lung volumes compared to predicted values (FVC, VA and TLC) and controls (FVC), while flow-based measures (FEV1) developed similarly across groups, suggesting that swimming selectively promotes lung volume growth rather than airway caliber or gas exchange.
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