IGF-1 is a hormone responsible for long bone growth in children and muscle growth and repair in adults. IGF1-LR3 is a more potent version of IGF-1 that induces muscle hyperplasia and increases muscle cell growth. It has a longer half-life and causes localized IGF levels to rise. It can also increase the uptake of supplements and prevent muscle loss in PCT. Its potency is due to decreased binding to IGF binding proteins.