Reproducibility, validity and predictors of six-minute walk test in overweight and obese adolescents with intellectual disability

Objectives: To assess the reproducibility and validity of the six-minute walk test (6MWT) and predictors of the six-minute walk distance (6MWD) in adolescents with overweight or obesity and intellectual disability (ID). Study design: Sixty-one adolescents with overweight or obesity and mild-to-moderate ID (intelligent quotient [IQ] 40-70; age 14-22 years) participated in this study. To test reproducibility, 39 of the participants performed the 6MWT twice with an interval of 1 week. To test validity (n = 39), peak oxygen uptake (peak VO2) was measured on a bicycle ergometer. For the predictor study (n = 61), weight, height, peak VO2 and quadriceps strength were measured, and IQ and orthopedic conditions were collected from the participants' medical records. Results: There was no significant difference between the means of the two 6MWTs (571.3 vs. 576.5 m; p = 0.452). The intraclass correlation coefficient was 0.82, indicating good reliability. The smallest real difference was 82.6 m. 6MWD correlated significantly with relative peak VO2 (beta = 0.69) indicating validity. Relative peak VO2, height, IQ, body mass index (BMI) and quadriceps strength are predictors of the 6MWD in this population. Conclusion: 6MWT is a reliable and valid test in adolescents with overweight or obesity and ID. Low IQ, overweight/obesity and low physical fitness contribute to the outcome of the 6MWT