Respiratory Muscle Strength in Brazilian Adolescents: Impact of Body Composition

(1) Introduction: Studies on respiratory muscle strength (RMS) in adolescents are controversial. Few studies so far have investigated respiratory muscle strength in Brazilian adolescents and the impact of body composition on it. (2) Objective: to evaluate the respiratory muscle strength of Brazilian adolescents and compare this with nationally and internationally predicted normality values. (3) Method: A cross-sectional study (CAEE: 34634414.5.0000.5479) was carried out with 98 adolescents, where both sexes were divided into four groups: eutrophic (n = 44); overweight (n = 15), obese (n = 25), and severely obese (n = 14). All were submitted to an anthropometric assessment, body composition analysis and manovacuometry. To interpret the results, Analysis of Variance (ANOVA) with Turkey’s post hoc test was used. The Kruskal–Wallis test and Friedman’s post hoc test were used to compare the observed vs. proposed results. A p-value < 0.05 was considered statistically significant. (4) Results: There were no differences among the groups for maximal inspiratory (MIP) and expiratory (MEP) pressures. However, when considering the total sample, we could say that RMS was higher among boys, and there were no significant differences in RMS in relation to the maturational stage. The values obtained for MIP were lower than those suggested for the national equation and higher than those proposed for the international equation. Similarly, the values obtained for MEP were lower than those suggested for the national and international equation. (5) Conclusions: RMS was similar in adolescents with different body compositions and different maturation stages. Adiposity did not interfere with RMS in adolescents. Boys had higher MIP and MEP values compared to girls. Therefore, the reference values proposed by the equations do not consistently match RMS in the adolescents studied. This context reinforces the need for new studies that are related to RMS to establish normality values and propose equations that represent the youth population.