The retest reliability of the six-minute walk test in patients referred to a cardiac rehabilitation programme

Background and purpose: The purpose of this paper was to determine if the Six-minute Walk Test (6MWT) was a reliable exercise test for patients referred to cardiac rehabilitation when up to three tests were performed and to determine if test scores differed according to between-test time interval.

Methods: Thirty adults aged 63 ± 7.9 years referred to cardiac rehabilitation participated in a repeated measures reliability trial. Participants completed three 6MWTs within a one-week period. Participants were randomly allocated to one of three groups: on the first day, Group A completed three walks, Group B completed two walks and Group C completed one walk. Relative reliability was expressed in a ratio (ICC(2,1) ), and absolute reliability was expressed in metres (95% confidence intervals) for group and individuals.

Results: The 6MWT demonstrated a high level of relative reliability (intraclass correlation coefficients [ICC] = 0.94) across the three walks. There was no statistically significant difference between the test scores of the three groups. However, there was an increase in distance walked from the first to the second to the third 6MWT. Absolute reliability indicated that a change of at least 44 m would be required to be interpreted as true change in a group, and at least 95 m to be interpreted as true change in an individual with 95% confidence.

Conclusion: Three 6MWTs completed in relatively short timeframes were not sufficient for reliable results as there was an increase in the distance walked, and relatively large increases in distances would be required to be interpreted as change. It did not make any difference whether the tests were all completed on one day or over one week. This study highlighted problems that may arise when relying on reliability coefficients alone to interpret reliability. These results suggest that the 6MWT may not have sufficient reliability to be a suitable test to evaluate exercise tolerance in patients referred to cardiac rehabilitation.