Validation of the Treadmill Six-Minute Walk Test in People Following Cardiac Surgery

Background. The Six-Minute Walk Test (6MWT) often is used to measure exercise capacity in people with cardiopulmonary diseases but has some disadvantages. The 6MWT administered on a treadmill (Tr6MWT) requires less physical space and allows for easier monitoring of vital parameters than the traditional 6MWT. Objective. The objectives of this study were: (1) to analyze the validity of the Tr6MWT in people who underwent cardiac surgery; (2) to compare the reliability, responsiveness, and people's tolerance of the Tr6MWT with those of the 6MWT; and (3) to evaluate the agreement between the 2 tests. Design. This study was designed to assess reliability and validity. Methods. Twenty-six participants who were inpatients were assessed before a 2-week rehabilitation program. Twenty of them also were assessed after rehabilitation. All participants performed 3 Tr6MWT trials and 3 6MWT trials that were randomly assigned on 2 consecutive days. Results. The Pearson r correlation coefficient between the Tr6MWT and the 6MWT was .72, indicating satisfactory concurrent validity. The Tr6MWT was as well tolerated as the 6MWT. The Tr6MWT produced reproducible results after 2 practice tests, whereas the 6MWT did so after only 1 practice test. Both tests showed high test-retest reliability (intraclass correlation coefficient of >.94; standard errors of measurement of 23 m for the Tr6MWT and 18.5 m for the 6MWT). The Tr6MWT showed better responsiveness than the 6MWT (effect sizes of 0.9 for the Tr6MWT and 0.6 for the 6MWT). The distance covered during the Tr6MWT was significantly shorter ((X) over bar =62 m, SD=91) before rehabilitation but not after rehabilitation. Limitations. A crossover randomized procedure could have improved the reliability of the Tr6MWT in people who performed the 6MWT first. Conclusions. The Tr6MWT appears to be an instrument with adequate concurrent validity and to be tolerable, reliable, and responsive for the evaluation of exercise capacity in people after cardiac surgery even though it is not interchangeable with the 6MWT.