Validity and clinical applicability of the 60-second sit-to-stand test in people with acute exacerbations of COPD

Background: The 60-s sit-to-stand test (60STS) is a simple and increasingly popular test of physical function, however evidence to support its appropriateness for assessing people with acute exacerbations of chronic obstructive pulmonary disease (AECOPD) is lacking. Aims: To evaluate the concurrent, convergent, predictive and discriminant validity, and responsiveness of the 60STS against the 6-min walk test (6MWT) in people hospitalised due to AECOPD. Methods: Prospective cohort study involving 54 inpatients with AECOPD (53% males, mean age 69.0 years, FEV1 46.5% predicted). 60STS was performed 30 min after a 6-min walk test (6MWT) upon discharge, with follow-up testing repeated one-month later (n = 39). Outcome measures included 60STS repetitions (60STSr), 6-min walk distance (6MWD), heart rate, oxyhaemoglobin saturation (SpO₂), perceived dyspnoea (Borg scale), and rate of perceived exertion (RPE). Concurrent validity was assessed via correlation, convergent validity via Bland-Altman plots, predictive validity via multivariate linear regression (adjusted for confounders), discriminant validity via unpaired t tests and responsiveness via χ² tests. Results: Discharge 60STSr and 6MWD were strongly correlated (r = 0.61). Bland-Altman plots for nadir SpO2, peak HR, Borg and RPE scores showed acceptable agreement in terms of mean differences, but wide limits of agreement. Poor 60STSr performers were older, had weaker quadriceps, and had lower 6MWD than high performers (p < 0.05 for all). 60STSr was not retained as a significant predictor of 6MWD in multivariate regression analyses. 80% of 60STSr improvers also improved >30 m on 6MWT at follow-up. Conclusion: The 60STS demonstrates satisfactory validity and responsiveness as a measure of exercise performance in people with AECOPD.