Reproducibility and minimal detectable change of sustained maximal inspiratory pressure in healthy adults

[Purpose] This study aimed to verify the reproducibility and minimal detectable change of sustained maximal inspiratory pressure measured using the test of incremental respiratory endurance, establishing it as an index of respiratory muscle function. [Participants and Methods] Thirty healthy young adults (mean age: 24.8 ± 2.7 years) participated. Sustained maximal inspiratory pressure was measured two or three times using the test of incremental respiratory endurance. Its relative and absolute reliabilities were assessed using the intraclass correlation coefficient and Bland-Altman analysis. The minimal detectable change and percentage of minimal detectable change were also calculated. [Results] The intraclass correlation coefficients for sustained maximal inspiratory pressure were 0.937 and 0.969, respectively, indicating high reliability across both re-measurement criteria. Bland-Altman analysis showed no systematic bias. Minimal detectable change values were 124.7 and 88.4 pressure time units, with corresponding percentage of minimal detectable change values of 23.8% and 16.9%, respectively. [Conclusion] Sustained maximal inspiratory pressure demonstrated high reliability and no systematic bias, suggesting its potential as a valid measure of respiratory muscle endurance. Using this measure as a reference for repeated measurements may enhance accuracy. Future research should assess its applicability in older adults and clinical populations.