Background: In children and adolescents, the anabolic effects of exercise are mediated through growth hormone (GH) and insulin-like growth factor-I (IGF-I). Therefore, this study aimed to compare the effects of combined endurance-resistance versus resistance-endurance exercises on GH and IGF-I in non-athlete prepubertal girls.

Materials and Methods: In this semi-experimental study, 16 prepubertal girls aged 9-11 years old, after homogenization, were randomly allocated into two equal groups (n=8): the endurance-resistance and resistance-endurance. Activities in both groups included combined endurance (20 minutes of moderate-intensity aerobic exercise with 60%-70% of the maximal oxygen uptake (VO2max) on a treadmill)-resistance (biceps, triceps, chest press, butterfly, knee extension and flexion, moderate leg press with 60% of 1-RM, and 1 set of 10 repetitions) and resistance-endurance training with different orders. Before, immediately after and 2 hours after the exercise, blood samples were taken and GH and IGF-1 levels were measured.

Results: Immediately after the training, in both group, GH levels (3.39 ng/ml vs 1.8 ng/ml) were significantly increased compared to the resting condition (0.77 ng/ml vs 0.72 ng/ml) (P=0.017). However, GH levels (0.97 ng/ml vs 0.18 ng/ml) were significantly decreased in both groups after 2 hours (P=0.012). The GH levels in the endurance-resistance group were higher compared to the resistance-endurance group. Changes in IGF-1 levels in both training groups before, immediately after and 2 hours after the training did not show significant differences.

Conclusion: It seems that combined endurance-resistance training is more appropriate option for non-athlete prepubertal girls.