In the present study, we examined the effects of trunk rotation posture in the sitting position for respiratory variables, such as vital capacity (VC), inspiratory capacity (IC), tidal volume (VT), expiratory reserve volume (ERV), inspiratory reserve volume (IRV), force vital capacity (FVC), forces expiratory volume in one second (FEV1.0), or forces expiratory volume % in one second (FEV1.0%), and respiratory muscles. It is known that posture and gender differences effects on pulmonary function. However, how trunk rotation affects respiratory variable in healthy young people remains unclear. This study’s main results were the rotational posture decrease in respiratory variables: VC, FVC, ERV, PEmax, and PImax.
The results showed significant decrease in VC and FVC during respiration in trunk rotation posture than that in the rest sitting posture. Lee et al. reported a reduced motion at the axilla of the rib cage during respiration with spinal rotation 12. The rotational posture causes a range of motion decrease in the rib cage, changing its articulations and intercostal muscle activities. This posture requires increased abdominal motion. It is suggested that this thoracoabdominal motion change induced the VC and FVC decreases.
Furthermore, the results indicated significant decrease in ERV and FEV1.0 during respiration in the rotational posture compared to that in the rest sitting posture. According to a previous study, obesity and external pressure on the rib cage reduced ERV 13. The muscle strength variables for forced expiration were significantly decreased in the rotational posture. The agonist muscle for trunk rotation includes the external and internal oblique abdominal muscles, which are the most active during forced expiration. Therefore, this result suggests that rotational posture limits the activity of the forced expiratory muscles.
PImax was significantly decreased in the rotational posture compared with that in the rest posture in females, although it did not change in males. It is known that chest wall kinematics is significantly influenced by gender 8, 9. There are differences in the relative contribution of the rib cage and abdomen during respiration. Bellemare et al. reported that the differences in the composition of thoracic dimensions and configuration between males and females produce differences in the contribution of the rib cage and abdomen during ventilation 5. Females have smaller airways relative to their lung size 1. We deduced that the rotational posture, restricting the range of motion of the rib cage, affected the inspiratory muscle strength for female.
This study exhibited that respiratory variables were significantly decreased by rotational posture even in healthy young people with average muscle strength. Therefore, the elderly or chronically ill patients speculated cause further affected by posture.