Statistical analysis
A sample size of 20 adolescents per group was estimated to be needed to detect a difference of 6 ml/kg/min with a standard deviation of 6 ml/kg/min in the VO2peak (22). The final sample size was 22 adolescents per group, assuming a loss of up to 10%. The sample size was calculated to provide 80% power and an alpha level of 0.05. The normality of the data was evaluated using the Kolmogorov-Smirnov test. The between-group comparisons of the categorical variables and the analysis of the differences in the proportions of adolescents across groups were performed using the chi-square test or Fisher’s test. For the between-group comparisons of the continuous variables, the t-test or Mann-Whitney test was used. The data were analyzed using the Statistical Package for Social Science (SPSS) software, version 22.0 (Chicago, IL, USA).