Minimal clinically important differences in the six-minute walk test and the incremental shuttle walking test

Simple walking tests are widely used for the assessment of functional status in patients with cardiorespiratory disorders. These tests require far less instrumentation than formal cardiopulmonary exercise tests, but they do require standardization of procedures to achieve reproducible results. The most widely used tests for patients with COPD are the 6-minute walking test (6MWT) and the incremental shuttle walking test (SWT). The 6MWT has been characterized in COPD patients with respect to reproducibility and responsivity to change in health status. The 6MWT results are correlated with pulmonary function, health-related quality of life, maximum exercise capacity, and mortality. The minimal clinically important difference (MCID) for the 6MWT is conservatively estimated to be 54-80 meters using both distributional and discriminative methods. For an individual patient, the 6MWT would need to change by about 86 meters to be statistically confident that there has been a change. The SWT has been less extensively validated than the 6MWT, but has similar reproducibility in COPD (CV = approximately 20%). The SWT results improve with pulmonary rehabilitation and bronchodilation, and are highly correlated with maximum oxygen consumption. There are no studies that address the issue of MCID for the SWT. In addition to the MCID, the design and interpretation of COPD clinical trials should take into account the severity of initial impairment, the asymmetry between positive and negative changes, the proportion of patients who show substantial improvement, and the costs and risks of the treatment.