Effect of Trunk Rotation and Sex Differences on Lung Volume and Respiratory Muscle Strength in Healthy Young People

Background Posture and trunk movements influence respiratory mechanics by altering rib cage mobility and thoracoabdominal motion. Trunk rotation frequently occurs during activities of daily living and may affect lung volumes and respiratory muscle function. Anatomical and physiological differences between males and females may also influence respiratory responses to posture. However, the combined effects of trunk rotation and biological sex on pulmonary function and respiratory muscle strength remain unclear. This study aimed to evaluate the effects of trunk rotation and sex differences on lung volume parameters and respiratory muscle strength in healthy young adults. Methodology A total of 20 healthy young adults (9 males and 11 females; mean age = 22 ± 1 years) participated in this study. Participants performed pulmonary function tests in the sitting position at the resting posture or in the sitting position with 30° trunk rotation. Lung function parameters, including vital capacity (VC), inspiratory capacity (IC), tidal volume (VT), expiratory reserve volume (ERV), inspiratory reserve volume (IRV), forced vital capacity (FVC), and forced expiratory volume in one second (FEV1.0), were measured using spirometry. Respiratory muscle strength was assessed using maximal inspiratory pressure (PImax) and maximal expiratory pressure (PEmax). Two-way repeated-measures analysis of variance was used to evaluate the effects of posture and sex. Results Significant main effects of sex were observed for several respiratory variables, including FVC, FEV1.0, VC, ERV, PImax, and PEmax, with males showing higher values than females. Significant main effects of posture were also observed for FVC, FEV1.0, VC, ERV, PImax, and PEmax, with lower values in the rotational posture than in the resting posture. A significant interaction between posture and sex was found for PEmax, with a greater decrease in males during trunk rotation. In contrast, PImax decreased significantly in the rotational posture only in females. Conclusions Trunk rotation in the sitting position reduces several lung volume parameters and respiratory muscle strength in healthy young adults, and the effects may differ between males and females. In particular, trunk rotation may affect forced expiration more in males and inspiratory muscle strength more in females. These findings provide fundamental data on the interaction between posture and sex in respiratory mechanics and may provide useful insights for respiratory assessment and rehabilitation strategies involving trunk movement.