When you reach adult age, the endogenous levels of HGH are diminished. After this, GH is still present in the body but at a way lower level where it continues to aid in protein synthesis, RNA and DNA reactions and also assures conversion of body fat to energy. By taking a high dose of this hormone, athletes are promoting these effects, causing the body to deposit more muscle tissue while at the same time reducing body fat stores. In other words perfect to gain muscle mass and get rid of the fat.