IGF 1 LR3 The Muscle Building Peptide Everyone's Talking About IGF 1 LR3 is one of the most powerful performance peptides used for muscle growth, recovery, and fat loss. It's a modified version Same molecule. Longer leash. IGF 1 LR3 is a long arginine 3 analog of insulin like growth factor 1. The Arg3 substitution prevents binding to IGFBP 3, the carrier protein that normally clears IGF 1 from circulation. Half life IGF 1 LR3 Kallista Labs Insulin Like Growth Factor 1 (IGF 1) and Its Monitoring in Medical Diagnostic and in Sports