Validity and Reproducibility of a New Treadmill Protocol: The Fitkids Treadmill Test

Purpose This study aimed to investigate the validity and reproducibility of a new treadmill protocol in healthy children and adolescents: the Fitkids Treadmill Test (FTT). Methods Sixty-eight healthy children and adolescents (6-18 yr) were randomly divided into a validity group (14 boys and 20 girls; mean ± SD age, 12.9 ± 3.6 yr) that performed the FTT and Bruce protocol, both with respiratory gas analysis within 2 wk, and a reproducibility group (19 boys and 15 girls; mean ± SD age, 13.5 ± 3.5 yr) that performed the FTT twice within 2 wk. A subgroup of 21 participants within the reproducibility group performed both FTT with respiratory gas analysis. Time to exhaustion (TTE) was the main outcome of the FTT. Results VO<inf>2peak</inf> measured during the FTT showed excellent correlation with VO<inf>2peak</inf> measured during the Bruce protocol (r = 0.90; P < 0.01). Backward multiple regression analysis provided the following prediction equations for VO<inf>2peak</inf> (L·min^-1) for boys and girls, respectively: VO<inf>2peak</inf> FTT = -0.748 + (0.117 × TTEFTT) + (0.032 × body mass) + 0.263, and VO<inf>2peak</inf> FTT = -0.748 + (0.117 × TTEFTT) + (0.032 × body mass) [R² = 0.935; SEE = 0.256 L·min^-1]. Cross-validation of the regression model showed an R² value of 0.76. Reliability statistics for the FTT showed an intraclass correlation coefficient of 0.985 (95% confidence interval, 0.971-0.993; P < 0.001) for TTE. Bland-Altman analysis showed a mean bias of -0.07 min, with limits of agreement between +1.30 and -1.43 min. Conclusions Results suggest that the FTT is a useful treadmill protocol with good validity and reproducibility in healthy children and adolescents. Exercise performance on the FTT and body mass can be used to adequately predict VO<inf>2peak</inf> when respiratory gas analysis is not available.