Modifying track layout from straight to circular has a modest effect on the 6-min walk distance

Background: The protocol used for the 6-min walk test (6MWT) influences its results. The only study to examine the effect of modifying track layout performed a retrospective analysis and concluded that institutions using continuous tracks yield greater distances than those using straight tracks. Agreement between the distances measured on different tracks could not be examined. We evaluated the effect of modifying track layout on walk distance and examined the agreement and repeatability of distances measured on different tracks. Methods: In a prospective, randomized, cross-over study, 27 COPD subjects (FEV1, 38 +/- 14% [mean +/- SD]; 15 men) attended three separate test sessions, completing six 6MWTs. To familiarize all subjects with both tracks, the first two sessions comprised two 6MWTs on either a circular or straight track. During the final session, each subject was tested once on the straight and once on the circular track. Results: The distance walked on the circular track exceeded the straight track by 13 +/- 17 m (p < 0.001). The limit of agreement between tracks was 33 m. Coefficient of repeatability values when the test was completed on different days for the straight and circular tracks were 51 m and 65 m, respectively. Conclusions: When evaluating changes in 6-min walk distance in groups of patients, track layout should be standardized. However, the effect of modifying track layout on an individual's walking distance is small compared to their daily variability in walk distance. Therefore, standardizing track layout for any given individual may be inconsequential when evaluating the change in distances from tests performed on different days.