BACKGROUND: The sit-to-stand (STS) test is a feasible tool for measuring peripheral muscle strength of the lower limbs. There is evidence of increasing use of STS tests in patients with COPD. We sought to evaluate in subjects with COPD the minimum clinically important difference in 30-s STS test after pulmonary rehabilitation.
METHODS: Stable COPD subjects undergoing a 30-s STS test and a 6-min walk test (6MWT) before and after pulmonary rehabilitation were included. Responsiveness to pulmonary rehabilitation was determined by the change in 30-s STS test results (Δ 30-s STS) before and after pulmonary rehabilitation. The minimum clinically important difference was evaluated using an anchor-based method.
RESULTS: 96 subjects with moderate-to-severe COPD were included. At baseline, 30-s STS test results were significantly related to distance covered in a 6MWT (6MWD) (r = 0.65, P < .001), FVC (r = 0.46, P < .001), PaCO2 (r = -0.42, P < .001), FEV1 (r = 0.39, P < .001), and age (r = -0.31, P = .002). After pulmonary rehabilitation, a significant improvement in 30-s STS test results was observed (mean difference +2 repetitions, P < .001). The Δ30-s STS was positively related to Δ6MWD (r = 0.62, P < .001), transitional dyspnea index (r = 0.67, P < .001), and baseline residual volume (r = 0.27, P = .007). The receiver operating characteristic curves method identified a Δ 30-s STS cut-off of 2 repetitions as the best discriminating value (area under the curve: 0.892, P < .001) to identify the minimum clinically important difference for Δ6MWD (30 m). In a multivariate logistic regression model, baseline 30-s STS (odds ratio 2.63; 95% CI 1.09-6.35, P = .031) and diffusing capacity of the lung for carbon monoxide (< 53% predicted) (odds ratio 2.49, 95% CI 1.04-5.98, P = .041) predict the risk to have a Δ 30-s STS ≥ 2 repetitions.
CONCLUSIONS: Our study indicates that in stable subjects with moderate-to-severe COPD, the 30-s STS test was a sensitive tool to assess the efficacy of pulmonary rehabilitation. A Δ 30-s STS of ≥ 2 repetitions represented the minimum clinically important difference, which may be predicted by the baseline ability in the 30-s STS test and lung function in terms of diffusing lung capacity (ClinicalTrials.gov registration NCT03627624).