Background: There are few studies related to effects of exercise training, including concurrent training, on hormonal changes in children. Hence, the aim of this study was to Compare theeffects of 6 weeks of resistance training and concurrent resistance and endurance training on aerobic power (VO2peak) and resting levels of growth hormone and cortisol in healthy children.

Materials and Methods: The subjects ofthis quasi-experimental study were 35 healthy boys between 9-11 years old, which were randomly divided into three groups of concurrent training (n=12), resistance training (n=11), control (n=12). Experimental groups were trained during 6 weeks 3 times a week.Control group were performed only their routine activities. VO2peak test was taken 48 hours before and after implementation of 6-weeks protocols and samples were selected from all subjects.Measurement of resting levels of GH and cortical was performed with ELISA method. For data analysis, one way ANOVA and paired t-test were used.

Results: The results showed that VO2peak and resting levels of GH increased significantly in concurrenttraining group (p=0.001, p=0.003, respectively). Resting level of cortisol in concurrent group was significantly lower than the other groups (p<0.05) and it was reducedsignificantlyin concurrent training and resistance training groups (p=0.001, p=0.036).

Conclusion: It seems a concurrent training period has greater benefits on VO2peak and resting levels of GH and cortical in children in comparison with resistance training.