New Protocol for Evaluating Maximum Inspiratory Pressure: Concurrent Validity and Test–Retest Reliability

Abstract Objective The purpose of this study was to validate a maximum inspiratory pressure test protocol based on the principles of the one-repetition maximum test, assess its test–retest reliability, and establish minimal detectable change in individuals with chronic obstructive pulmonary disease (COPD). Methods Forty-nine individuals with COPD were included in the study, of whom 44 individuals attended 2 appointments separated by 7 to 10 days for test–retest reliability. The maximum inspiratory pressure test was performed using a threshold valve device (one-repetition maximum-based protocol) and the digital manometer (reference test). The one-repetition maximum-based protocol consisted of an incremental phase (inspiratory load increase 10 cmH2O to achieve respiratory failure) and an approach phase (load halfway between the lowest failed attempt and the last valid attempt was prescribed). Results The concurrent validity of the one-repetition maximum-based protocol for the maximum inspiratory pressure test was good with respect to the reference test (day 1, ICC = 0.81; day 2, ICC = 0.85). The test–retest reliability was excellent (ICC = 0.92), with a standard error of measurement of 6.3 cmH2O and a minimal detectable change of 17.5 cmH2O. Conclusion This study validated a new one-repetition maximum-based protocol for the maximum inspiratory pressure test using an inspiratory muscle training device in individuals with COPD, showing good concurrent validity compared with the reference test, as well as excellent test–retest reliability. The minimal detectable change reported can be interpreted and applied in the clinical setting. Impact There was a need for developing new, inexpensive, simple, and feasible methods for the maximum inspiratory pressure test. The validation of the one-repetition maximum-based protocol addresses this issue, allowing for the appropriate prescription of inspiratory muscle training, favoring its widespread use in people with COPD and therefore improving their physical therapist care.