A long-acting IGF-1 analogue with reduced binding-protein affinity and enhanced tissue anabolic activity.
Binds IGF-1 receptors with similar affinity to native IGF-1 but has ~3× reduced affinity for IGF binding proteins (IGFBPs), meaning a greater free fraction reaches target tissues. Drives protein synthesis via PI3K/AKT/mTOR, activates muscle satellite cells, and inhibits protein degradation pathways.
The 'LR3' designation refers to an N-terminal 13-amino-acid extension (Long) and an arginine substitution at position 3, which together reduce IGFBP binding and extend half-life from ~15 minutes (native IGF-1) to ~20 hours.
Often used in combination with PEG-MGF: PEG-MGF activates satellite cells post-exercise, then IGF-1 LR3 drives the proliferation of those activated cells — a synergistic muscle repair protocol.