The aim of this study was to investigate the effect of resistance training with different intensities on serum myostatin and follistatin levels in sedentary young women. Twenty four young, sedentary women were assigned to either an 8-week high or low intensity resistance training program in a circular shape, involving 3 training sessions per week. Based on the equation of one repetition maximum (1RM), the training program for both groups was isocaloric. The training protocol consisted of four lower body exercises (leg extension, leg flexion, squat, and standing calf raise) and three upper body exercises (high pull, elbow flexion, and elbow extension) performed at both low intensity (40%–60%1RM and 20–30 repetition in each station) and high intensity (70%–90% 1RM and 5–15 repetition in each station). Blood samples were taken before and after eight weeks of resistance training. The procedure was performed by standard antecubital venous puncture. Blood samples were collected after 12 h fasting, and then the samples were clotted for two hours at room temperature before centrifugation for 15 min at 1000 × g. Serum was stored at −20 °C for 2 months until the time of analysis. Serum Myostatin and Follistatin concentrations were determined using ELISA Kit.one-way ANOVA was conducted for determining the homogeneity of the groups before starting the exercise program, and repeated measure analysis of variance method was implemented to compare the means between the groups, and to compare the means within the groups as well. For all analysis, statistical significance was assigned at P < 0.05. In the low-intensity RT group, no significant changes were observed in Follistatin serum (P = 0.649), whereas it increased significantly (P = 0.040) in the high intensity RT group. Nevertheless, the variance between groups in Follistatin was not significant (P = 0.086). In the high intensity RT group, Myostatin serum decreased significantly (P = 0.041), whereas the ratio of Follistatin to Myostatin increased dramatically (P = 0.951). In this case, the variance between the groups was not significant for both Myostatin (P = 0.211) and the ratio of Follistatin to Myostatin (P = 0.060). Statistical analysis showed that eight weeks of high intensity resistance training significantly increased both Follistatin and the ratio of Follistatin to Myostatin. It also significantly reduced the amount of Myostatin in sedentary young women. According to studies, it seems that Myokines’ release rate and regulate factors of muscle growth depend on the exercise intensity and the volume of muscles involved. It seems that High intensity resistance training develops their muscular tissue through increasing the Follistatin levels and decreasing the Myostatin levels in sedentary women.

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