Six-minute walk test in obese children and adolescents: reproducibility and validity.

BACKGROUND AND PURPOSE: The six-minute walk test (6MWT) is increasingly used in clinical practice. The aims of this study were to determine the reproducibility of the 6MWT in obese children and adolescents, to describe walking capacity in this population and compare the results with values from normal-weight children (known group validity), and, finally, to describe the correlation between distance walked and estimated maximum oxygen uptake (VO(2)max).

METHODS: Reproducibility was determined by a test-retest design and known group validity by a comparative design. The 6MWT was first test-retested in 49 obese children (30 boys, 19 girls, 8-16 years, body mass index [BMI] 24.9-52.1 kg?m(-2)). Then, for validation, 250 obese children (126 boys, 124 girls, 8-16 years, BMI 23.2-57 kg/m(2)) and 97 normal-weight children (48 boys, 49 girls, 8-16 years, BMI 13.3-23.2 kg.m(-2)) performed the 6MWT. The obese children also performed a sub-maximal bicycle ergometry test.

RESULTS: In the test-retest, the obese children walked 571 m the first test and 57 m the second (p = 0.578). The measurement error (S(w)) was 24 m, coefficient of variation (CV): 4.3% and the intraclass correlation (ICC1:1): 0.84. Repeatability was 68 m, and limits of agreement were +71 and -65 m. In comparison mean (standard deviation), six-minute walk distance (6MWD) in the obese children was 571 m (65.5), and in the normal-weight children, 663 m (61.1) (p < 0.001). The correlation between 6MWD and estimated VO(2)max (r = 0.34) was low.

CONCLUSIONS: The 6MWT showed good reproducibility and known group validity, and can be recommended for use in clinical practice in the studied population. To evaluate individual outcomes after intervention, the 6MWD needs to change by >68 m to be statistically significant. The 6MWD performed by obese children averaged 86% of the distance normal-weight children walked. In obese children, the correlation between 6MWD and estimated VO(2)max was low, hence the 6MWT cannot substitute a bicycle ergometry test.