The six-minute walk test in outpatients with obesity: reproducibility and known group validity

To assess the reproducibility and validity of the six-minute walk test (6MWT) in men and women with obesity in order to facilitate evaluation of treatment outcome.

A test--retest design was used to test reproducibility and a comparative design to test known group validity. Forty-three obese outpatients (16 male), mean age 47 (21-62) years, mean body mass index (BMI) 40 (3-62)kg-m(-2) performed the 6MWT twice within one week. Intraclass correlation (ICC1.1) and measurement error (S(w)) were calculated from the mean square values derived from a one-way repeated-measures ANOVA (fixed effect model). The reproducibility was also analysed by means of coefficient of variation (CV) and the Bland Altman method including 95% limits of agreement. The variance of the distance walked was analysed by means of regressions. The known group validity of the 6MWT (distance walked and the work of walking) in obese participants was shown by comparisons with 41 lean participants (18 male), mean age 47 (24-65) years, mean BMI 22.7 kg-m(-2) (19-25).

The obese group walked 534 m (confidence interval [CI] 508-560 the first and 552 m (CI 523-580) the second walk (p < 0.001). S(w) was 25 m, CV 4.7%, ICC1.1 was 0.96. The limits of agreement were -46 m+80 m. The validity tests showed that they walked 162 m shorter (p < 0.001) and performed much heavier work (p < 0.001) than the lean group. In the obese group, BMI alone explained 38% of the variance of the distance walked.

The 6MWT showed good reproducibility and known group validity and can be recommended for evaluating walking ability in subjects with obesity. For individual evaluation, however, an improved walking distance of at least 80 m was required to make the difference clinically significant. Despite shorter walking distance the obese participants performed heavier work than the lean.