Morphological and functional characterization of respiratory muscles in male runners across different race distances: an ultrasound and physiological assessment

Running performance depends not only on aerobic capacity but also on the functional integration of the respiratory system and core musculature. However, morphological and functional adaptations of the diaphragm and abdominal muscles across different running disciplines remain insufficiently characterized. The aim of this study is to analyze diaphragm and abdominal muscle morphology using ultrasound, as well as respiratory muscle strength and pulmonary function, in amateur runners classified according to their primary competition distance.

A cross-sectional observational study was conducted including recreational and competitive male runners (18–60 years) with at least two years of training experience. Participants were divided into 3 groups: 5–10 km, half-marathon, and marathon. Diaphragm thickness at end-inspiration (Tdi,ei) and end-expiration (Tdi,ee), and diaphragm thickening fraction (DTF) were assessed by ultrasound. Abdominal muscle thickness (RA, EO, IO, and TrA) was also measured. Respiratory muscle strength was assessed using maximal inspiratory (MIP) and expiratory pressures (MEP), and pulmonary function by spirometry. Group comparisons were performed using one-way ANOVA.

Runners specializing in marathon showed significantly greater diaphragm thickness (Tdi,ei and Tdi,ee) and higher MIP compared with runners specializing in 5–10 km (p < 0.05). Additionally, IO thickness was significantly greater in runners specializing in half-marathon. No significant differences were observed in FEF25–75%, FEV1 or FVC between groups. These findings indicate distance-dependent adaptations in both inspiratory and expiratory musculature.

These findings indicate that running specialization is associated with distance-dependent morphological and functional adaptations of the respiratory system. Marathon runners show greater diaphragm thickness and inspiratory muscle strength, while half-marathon runners exhibit increased IO thickness. No differences in standard spirometric parameters were observed between groups, suggesting that these adaptations are primarily reflected in respiratory muscle structure and strength rather than conventional pulmonary function measures in amateur runners.