Comparative effects of inspiratory and expiratory muscle training on diaphragm adaptations and respiratory function in adolescent athletes: a randomized-controlled study

This study aimed to investigate the comparative effects of Inspiratory and Expiratory Muscle Training ( IMT and EMST) on diaphragm thickness and stiffness, and respiratory muscle performance in adolescent athletes. In this randomized controlled study, 26 adolescent female volleyball players were randomly assigned to the IMT and EMST groups. Both interventions were performed for 4 weeks, 5 days per week, twice daily. Diaphragm thickness and stiffness, pulmonary function, maximal inspiratory and expiratory pressure (MIP, MEP), and respiratory muscle endurance (Tmax) were evaluated at baseline and post-intervention. Significant time effects were observed for diaphragm thickness during inspiration and expiration and for MIP and MEP (all p < 0.001). However, no significant group × time interactions were detected ( p > 0.05). A significant time effect was observed for PEF% ( p = 0.022), while no significant group × time interaction was detected for pulmonary function parameters ( p > 0.05). Diaphragm stiffness and Tmax did not change significantly over time, and no significant group × time interactions were detected ( p > 0.05). Improvements in diaphragm thickness and respiratory muscle strength were observed in both the IMT and EMST groups in adolescent athletes. Respiratory muscle training added to regular sports training may be associated with structural and strength adaptations in adolescent athletes. ClinicalTrials.gov, NCT06759779, Registered 6 January 2025. Retrospectively registered.