Manual testing of respiratory muscles in adults with asthma: a intra and interrater reliability and validity study

Background: Manual Muscle Testing (MMT) is a useful tool to evaluate ventilatory mechanics in adults with asthma. However, in the reviewed literature, there are few studies that report psychometric features of this test. Therefore, the present study aimed to evaluate MMT reliability and validity in respiratory muscles in adults with asthma. Methods: Herein a cross-sectional study of diagnostic tests was developed. Measurements were carried out by two randomly assigned independent evaluators. Variables as muscle strength (MMT and static respiratory pressures), sociodemographic, anthropometric and disease-related were included. MMT reliability was evaluated using weighted kappa. Convergent validity was evaluated by comparing MTT and respiratory pressure measurements using Pearson’s correlation coefficient. The significance level was p <0.05. Results: Twenty-six adults with stable asthma participated in the study. The intrarater reliability found for MMT was between moderate and substantial (kappa=0.45-0.88) for all evaluated muscles. The determined interrater reliability was between slight and fair for intercostal muscles (kappa=0.07-0.24), and fair and substantial (kappa=0.36-0.75) for other muscles. The convergent validity of MMT and respiratory pressures was low (r=0.20-0.48). Conclusions: MMT is a reliable measurement that can be used to evaluate respiratory muscle strength in adults with asthma. This study support MMT application for respiratory muscles at clinical settings when more objective measures such as MIP and MEP are not available. Taking into account that the MMT is a useful, practical, low cost tool commonly used by physiotherapists, future studies could evaluate the convergent validity compared with dynamometry or electromyography of the respiratory muscles.