Huma Peptide IGF 1 LR3 Lean Muscle Growth & Recovery Mechanisms of IGF 1 Mediated Regulation of Skeletal Muscle Hypertrophy and Atrophy The mighty protein: insulin like growth factor type 1 The Physiological Society 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