IGF 1 LR3 does not promote growth in late gestation growth restricted fetal sheep American Journal of Physiology Endocrinology and Metabolism American Physiological Society Insulin Like Growth Factor 1 (IGF 1) and Its Monitoring in Medical Diagnostic and in Sports IGF 1 LR3 1mg Insulin Like Growth Factor IGF 1 LR3 (Insulin like Growth Factor 1 Long R3) is often called the "Holy Grail" of muscle building peptides because of its potent anabolic effects. In a Med Spa context, it is typically sought out HGH vs IGF 1 LR3: Scientific Comparison & Research Guide