Six Minute Walk Distance: Reference values in healthy Italian children

Introduction The 6-minute walk test (6MWT) is a simple assessment tool to evaluate exercise capacity. The result of the test is the distance that a subject can walk at a constant and normal pace within 6 minutes (6MWD) and reflects walking function at a submaximal level1. Use of 6MWT on healthy children has been relevant to assess exercise tolerance2 and to compare it to pathological conditions3. Our aim was to find reference values for the 6MWT in healthy Italian children. Methods The 6MWT was performed by 5614 children between 6 and 11 years, following the instructions outlined in the ATS guidelines1. Summary statistics are expressed as means and standard deviations or percentages, as appropriate. Age related percentiles (mean±SD of 3rd, 10th, 25th, 50th, 75th, 90th and 97th centiles) of the 6MWD were developed for males and females. Pearson's correlation coefficients were calculated between 6MWD and demographic data. A multiple linear regression model was assessed to predict expected 6MWT performance. All analyses were conducted using STATA/SE, a p value of less than 0.05 was considered significant. Results Males walked longer distances than females, respectively 598.8±83.9 m vs 592.1±77.6 m (p=0.0016). Values ranged between 513.3±60.4 m for 6 years old children to 656.1±71.6 m for 11. The 50th percentile values resulted in 511 m, 554 m, 603 m, 624 m, 649 m and 670.8 m for boys aged 6 to 11 years old, respectively. Differently the 50th percentile values resulted in 512 m, 543 m, 597 m, 620 m, 643 m and 655 m for girls aged 6 to 11 years old, respectively. A moderate correlation was found between 6MWD and age, weight and height (respectively rho = 0.58; 0.32; 0.52; p < 0.0001). In regression analysis, we found that age, gender and height were positively related to 6MWD, while weight was negatively related with 6MWD [6MWD = 107.91 + 25.02× age (years) +7.52× gender (M) +2.62× height (cm) −2.25× weight (Kg)]. Conclusion Reference values were established for the 6MWT in Italian healthy children. The 6MWD percentiles according to age provided a useful tool in the assessment of capacity in children aged 6-11 years.