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

The purpose of this study was to validate a maximum inspiratory pressure (MIP) test protocol based on the principles of the 1-repetition maximum (1RM) test, assess its test-retest reliability, and establish minimal detectable change (MDC) in individuals with chronic obstructive pulmonary disease (COPD).

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 MIP test was performed using a threshold valve device (1RM-based protocol) and the digital manometer (reference test). The 1RM-based protocol consisted of an incremental phase (inspiratory load increase [10 cm H2O] to achieve respiratory failure) and an approach phase (load halfway between the lowest failed attempt and the last valid attempt was prescribed).

The concurrent validity of the 1RM-based protocol for the MIP test was good with respect to the reference test (day 1, intraclass correlation coefficient [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 cm H2O and a MDC of 17.5 cm H2O.

This study validated a new 1RM-based protocol for the MIP test using an inspiratory muscle training (IMT) device in individuals with COPD, showing good concurrent validity compared with the reference test, as well as excellent test-retest reliability. The MDC reported can be interpreted and applied in the clinical setting.

There was a need for developing new, inexpensive, simple, and feasible methods for the MIP test. The validation of the 1RM-based protocol addresses this issue, allowing for the appropriate prescription of IMT, favoring its widespread use in people with COPD, and therefore improving their physical therapist care.