Influence of body mass index and physical activity level on respiratory muscle strength and lung function in adolescents

Abstract

OBJECTIVE: To evaluate respiratory function and verify whether body mass index (BMI) and physical activity level (PAL) influence muscle strength and lung function in adolescents. METHODS: Cross-sectional study with 123 adolescents aged 13-18 years. The adolescents were classified into two groups according to BMI. BMI was calculated and the variables measured were: waist circumference, bioimpedance parameters, fat-free mass and body fat. PAL was estimated by a specific instrument, respiratory muscle strength (maximum inspiratory pressure-MIP and maximum expiratory pressure-MEP) by manovacuometry and lung function by spirometry (forced vital capacity-FVC, forced expiratory volume in the first second-FEV 1 and FEV 1 /FVC). RESULTS: The prevalence of overweight was 26.8%. PAL did not show a significant difference between the groups (p=0.69). MIP (p=0.007) and FVC (p=0.005) were higher in overweight adolescents and the FEV 1 /FVC ratio was lower (p=0.001). Multiple regression showed that BMI and PAL adjusted for sex, age and sexual maturity were predictors of MIP, explaining the relationship by 30% and of FEV 1 /FVC by 9%. BMI was a predictor of FEV 1 (adjusted R 2 = 48%, p=0.001) and FVC (adjusted R 2 = 51%). CONCLUSION: Overweight adolescents had higher MIP and FVC and the FEV 1 /FVC ratio was lower. It is believed that PAL and BMI directly influence respiratory muscle strength and lung function in adolescents.