Background: The Incremental Shuttle Walking Test (ISWT) is used to assess exercise capacity in chronic obstructive pulmonary disease (COPD) and is employed as an outcome measure for pulmonary rehabilitation. This study was designed to establish the minimum clinically important difference (MCID) for the ISWT.
Methods: 372 patients (205 male) performed an ISWT before and after a 7 week outpatient pulmonary rehabilitation programme. After completing the course subjects were asked to identify, from a 5-point Likert scale, the perceived change in their exercise performance immediately upon completion of the ISWT. The scale ranged from 'better' to 'worse'
Results: The mean (SD) age was 69.4 (8.4) years, FEV1 1.06 (0.53) litres, and FEV1/FVC ratio 50.8 (18.1) %. Baseline shuttle walking test distance was 168.5(14.6) m. After rehabilitation this increased to 234.7 (125.3) m. The mean difference and 95% confidence interval for the difference was 65.9 (58.9 to72.9) m. For a subject to feel they were 'slightly better' the mean improvement was 47.5 (38.6 to 56.5) m and to report feeling 'better' the mean increase was 78.7 (70.5 to 86.9) m. Patients who reported that their exercise tolerance was 'about the same' increased by a mean of 18.0 (4.5 - 31.5)m.
Conclusion: Two levels of improvement were identified . The minimum clinically important improvement for the ISWT is 47.5m. In addition patients were able to distinguish an additional benefit at 78.7m.