Purpose: The 6-Minute Walk Test (6MWT) and Incremental Shuttle Walk Test (ISWT) are used to assess exercise capacity, but the reliability and responsiveness of these tests in individuals with non-cystic fibrosis (CF) bronchiectasis have not been determined. This study aimed to determine the reliability and responsiveness of both tests in adults with non-CF bronchiectasis.
Methods: Eighty-five participants completed 2 6MWTs and 2 ISWTs in random order. Testing was repeated at the conclusion of an 8-week intervention period of exercise training. Reliability was assessed using intraclass correlation coefficients (ICC) and Bland-Altman analysis. Responsiveness was measured by effect size (ES) and standardized response mean (SRM).
Results: At baseline, test-retest reliability was high for both tests (ICC ≥ 0.95). The mean (95% CI) increase in the 6MWT from test 1 to test 2 was 20 m (13-26 m): 3% (0-5%) change. The mean (95% CI) increase in the ISWT was 15 m (4-25m): 4% (2-6%) change. A significant learning effect persisted after 8 weeks for the 6MWT (P = .04), but not the ISWT (P = .61). The 6MWT ES was 0.32 and SRM was 0.68; for the ISWT, ES was 0.42 with SRM of 0.71.
Conclusion: The 6MWT and ISWT are reliable measures of exercise capacity in non-CF bronchiectasis and responsive to exercise training. The small learning effect in both measures at baseline suggests that 2 of each test are necessary to correctly assess exercise capacity. Completion of 2 6MWTs at followup may minimize the risk of underestimating a treatment effect.
Trial registration: ClinicalTrials.gov NCT00885521.