Reproducibility, validity, and reliability of the incremental step test for subjects with moderate to severe asthma

Objective: We investigated the measurement properties of the incremental step test in subjects with moderate to severe asthma. Methods: Subjects with moderate to severe persistent asthma were recruited from a tertiary university hospital specializing in treating severe asthma. All subjects performed one cardiopulmonary exercise test (CPET) and two incremental step tests (IST) in random sequences. Pulmonary gas exchange was measured during all exercise tests. The measurement properties investigated were reliability by intraclass correlation coefficient (ICC), measurement error by the standard error of measurement and minimum detectable difference, construct validity by Pearson's correlation, and interpretability by the ceiling and floor effects. Results: Fifty subjects (38 females, mean [SD], age 43.7 [11.6] yr, % FEV1 70 [14.3], BMI 28.5 [5.3] kg/m(2)) completed the study. The peak oxygen uptake (peak VO2) for the CPET was 27.6 [+/- 6.8] ml/kg/min, for the first IST was 22.3 [+/- 5.3] ml/kg/min and for the second IST was 23.3 [+/- 5.3] ml/kg/min. The IST presented excellent reliability (ICC=0.93, CI95% 0.88-0.96), very good measurement error (2.5%), and construct validity for peak VO2 measurement compared to the CPET (r = 0.85; p < 0.001) to assess exercise capacity in subjects with moderate to severe asthma, with appropriate ceiling (10%) and floor (0%) effects. Conclusion: The IST presented excellent reliability and very good measurement error and validity to assess exercise capacity in subjects with moderate to severe asthma, without ceiling or floor effects.