Incremental Step Test Results Are Related to the Six-Minute Walk Distance in Adults with Chronic Obstructive Pulmonary Disease: an Experimental Study

Background: The incremental step test (IST) could potentially be used to prescribe exercise training in people with COPD. Objective: To examine the relationship between IST total step count (ISTC) and 6MWT distance (6MWD) to determine whether an appropriate walking training prescription can be inferred from the ISTC. Methods: People with COPD were recruited after a PR assessment (including two 6MWTs) and performed one IST. Pearson’s correlation coefficient (r) assessed the relationship between ISTC, 6MWD and other independent variables. An estimated 6MWD equation from ISTC was derived through stepwise linear regression analysis and Bland Altman plots determined agreement between predicted 6MWD based on ISTC and actual 6MWD. Results: Thirty participants (mean [SD] age 74 [7] and FEV1 58 [21] % predicted) completed testing. Mean [SD] ISTC and 6MWD was 86 (40) and 462 (94) metres respectively. A strong positive correlation was found between ISTC and 6MWD (r = 0.82, p<0.001). ISTC and height (r = 0.32, p <0.001) and age (r = 0.22, p <0.003) were weakly associated. The estimated 6MWD equation from the stepwise regression was 6MWD (m) = 1.92 (ISTC) + 296.7. Conclusion: The IST could estimate 6MWD in people with COPD as the tests are strongly correlated.