The Trunk Rotation may Differentially Affect Lung Volume and Respiratory Muscle Strength in Males and Females

It is known that gender affect pulmonary function, associated with anatomical differences between male and female. However, the effects of trunk rotation on respiratory variables and its differences between males and females remain unclear. We examined the effects of gender and physical characteristics on postural changes in healthy young people. In this study, 9 males and 11 females (22 ± 1 year old for both males and females) were enrolled. We measure the vital capacity (VC), inspiratory capacity (IC), tidal volume (VT), expiratory reserve volume (ERV), inspiratory reserve volume (IRV), and force vital capacity (FVC) and respiratory muscle (PImax and PEmax) with rest posture in the sitting position (rest posture) in sitting position and 30° trunk rotation both genders in the sitting position (rotational posture). The value of VC, IC, ERV, IRV, FVC, or FEV1.0 for males were signicantly higher than that for females in both postures. Further, PEmax was more affected by rotational posture in male than in female. On the other hand, PImax showed a signicant decrease in the rotational posture only in females. This study indicated that the effect of rotational posture on PImax and PEmax, a measure of respiratory muscle strength, may be different between males and females. These nding may provide important insights on gender differences in respiration in daily living.


Introduction
It is known that there are signi cant differences in pulmonary function between male and females.
Females are characterized by a smaller-sized rib cage and airways relative to lung size (1) , (2) , (3) , (4) and a greater contribution of inspiratory rib cage muscles than males (5). These anatomical differences between males and females may affect performance in activities of daily living (ADL).
Posture also affects pulmonary function and the contribution of the rib cage and abdomen. Previous studies have investigated posture effect on chest wall kinematics (Craig 1960). Verschakelen et al. have showed the effect of gender on chest wall kinematics (7). There are differences in the composition of thoracic dimensions and con guration between genders (8) , (9). However, few studies have examined the effects of gender and physical characteristics on respiratory changes relative to posture.
In this study, we attempt to elucidate the effects of gender and physical characteristics on respiratory variables during rotational posture in healthy people.

Subjects
There were 20 healthy young people (22 ± 1 year old for both genders) were enrolled in this study. The inclusion criteria were nonsmoker and with no cardiac and pulmonary diseases.

Pulmonary function
Pulmonary function was assessed using a spirometer (H-801, CHEST, Japan), according to ATS/ERS statement on pulmonary function test (10). The 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%), were measured. Respiratory muscle strength was determined by measuring the maximal inspiratory pressure (PImax) and maximal expiratory pressure (PEmax) using a mouth pressure meter (IOP-01, Kobata, Japan), following ATS/ERS statement on respiratory muscle testing (11). The maximum value of the three maneuvers varying by less than 20% was recorded. These variables were measured in the resting or 30° trunk rotation in the sitting position. Participants performed a test in two sitting postures with rest period.

Statistical analysis
Respiratory variables are expressed as mean ± standard deviation. The data were analyzed using the IBM

Results
Twenty healthy young people participated in this study. The characteristics of participants are shown in Table 1. The participants performed pulmonary function test in the resting or 30° trunk rotation in the sitting position. Respiratory variables (VC, IC, VT, ERV, IRV, FVC, FEV1.0, and FEV1.0%) and respiratory muscle strength variables (PImax and PEmax) were measured in each posture. The value of VC, IC, ERV, IRV, FVC, or FEV1.0 for males were signi cantly higher than that for females in both postures (Table 2). Table 2 Differences in respiratory and respiratory muscle variables during the rest or rotational posture in sitting position between male and female Figure 1 shows the results of the two-way ANOVA with repeated measures and post-hoc analysis. There A signi cant interaction between gender and posture was observed in PEmax (F 1, 18 =7.5, p<0.05). In PEmax, the rotational posture decreased the male value more in males than in females.

Discussion
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 All data are presented as mean ± standard deviations.
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: FVC, FEV1.0, VC, ERV, PEmax, and PImax.
The results showed signi cant 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.
The results indicated signi cant decrease in ERV and FEV1.0 during respiration in the rotational posture compared to that in the rest sitting posture. Moreover, PEmax was more affected by rotational posture in male than in female. According to a previous study, obesity and external pressure on the rib cage reduced ERV (13). The muscle strength variables for forced expiration were signi cantly 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. It is known that chest wall kinematics is signi cantly in uenced 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 con guration between males and females produce differences in the contribution of the rib cage and abdomen during ventilation (5). The signi cant interaction between posture and gender for PEmax suggested that males may be more affected by the limitation of trunk rotation during forced expiration due to the higher contribution of the abdomen during respiration.
PImax was signi cantly decreased in the rotational posture compared with that in the rest posture in females, although it did not change in males. 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 signi cantly decreased by rotational posture even in healthy young people with average muscle strength. The effect of rotational posture on PImax and PEmax, a measure of respiratory muscle strength, may be different between males and females. Therefore, the elderly or chronically ill patients speculated cause further affected by posture.