If your priority is building muscle, IGF 1 is what really matters. What is IGF 1 LR3?, Insulin Like Growth Factor 1 Long R3 (IGF 1 LR3) is a modified version of IGF 1 with a longer half life, making it significantly more potent and effective for muscle growth, IGF 1 LR3 does not promote growth in late gestation growth restricted fetal sheep American Journal of Physiology Endocrinology and Metabolism American Physiological Society 5 Powerful Benefits (and Risks) of the IGF 1 LR3 and Hexarelin Stracuzzi Wellness