Question: What is the intra and inter-rater reliability of MMT of the diaphragm, external intercostal and abdominal muscles in a population of patients with asthma?, and What is the convergent validity of MTT against MIP and MEP in a population of patients with asthma?. Design: Herein a cross-sectional study of diagnostic tests was developed. Measurements were carried out by two randomly assigned independent evaluators. Participants: adults with stable asthma in stable phase of disease. Outcome measures: 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 intra-rater reliability found for MMT was between moderate and substantial (kappa=0.45-0.88) for all evaluated muscles. The determined inter-rater 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). Conclusion: MMT is a reliable measurement that can be used to evaluate respiratory muscle strength in adults with asthma. In the clinical setting, MMT contributes to an unbiased assessment and in the research scope, it is useful to support intervention outcomes by reducing the likelihood that results be affected by measurement variability.