LONG R IGF I Cell proliferation bioactivity of purified IGF 1 LR3 IGF 1. (A) Download Scientific Diagram Muscle Building Hormones: The Science of HGH & IGF 1 Thomas DeLauer YouTube There's a lot of confusion around peptides and muscle. Here's how I actually think about it. Most peptides don't build muscle directly. They improve the systems that allow muscle to grow. First, Late life targeting of the IGF 1 receptor improves healthspan and lifespan in female mice Nature Communications