Relationships between respiratory muscle strength, chest wall expansion, and functional capacity in healthy nonsmokers

Chest wall expansion determines lung volume and functional capacity. Factors determining chest wall expansion include respiratory muscle strength. Accordingly, there may be association among respiratory muscle strength, chest wall expansion, and functional capacity. Thusly, this cross-sectional study identified the relationship between respirato-ry muscle strength, chest wall expansion, and functional capacity. Seventy-six healthy male and female participants aged between 20 to 59 years exhibiting a body mass index of 18.5 to 22.9 kg/m(2) were enrolled. Inspiratory and expiratory muscle strength were evaluated via maximum inspiratory pressure (MIP) and maximum expiratory pressure (MEP), respectively. Chest wall expansion was measured through thoracic circumferences at three different levels; upper, middle, and lower levels with diaphragmatic movement also measured utilizing the circumference of the lower edge of the 10th rib. Functional capacity was evaluated through distance obtained from a 6-min walk test. Results showed that both MIP and MEP were significantly correlated with chest wall expansion at the middle (P=0.005 and P=0.006) and lower (P=0.012 and P=0.020) thoracic levels as well as diaphragmatic movement (both P<0.001). Moreover, both MIP and MEP were significantly related amid the 6-min walk distance (P=0.025 and P<0.001). In conclusion, respiratory muscle strength is positively associated with chest wall expansion, diaphragmatic movement, and functional capacity in healthy participants.