IGF-1 LR3

What it is: IGF-1 LR3 (Long R3 Insulin-Like Growth Factor-1) is a synthetic recombinant 83-amino-acid polypeptide containing the complete 70-amino-acid native human IGF-1 sequence with an Arg3 substitution and an additional 13-amino-acid N-terminal peptide extension.

How it works: The N-terminal peptide extension and Glu3Arg substitution dramatically reduce its binding affinity for endogenous IGF-Binding Proteins (IGFBPs) by over 100-fold. This prevents physiological sequestration, increasing biological bioavailability and extending its active receptor-binding half-life from ~20 minutes to over 20–30 hours. It activates the IGF-1R tyrosine kinase cascade, driving mTOR signaling, cellular hyperplasia (new muscle fiber recruitment), satellite cell proliferation, and amino acid uptake.

Why researchers study it: Extensively studied for muscle satellite cell activation, true cellular hyperplasia, enhanced nitrogen retention, accelerated soft tissue repair, and reversing catabolic muscle wasting.