I have not studied IGF as of yet, but I did find this on another site I frequent. Hope this helps.
Regular IGF only has a half-life of about 10-20 minutes in the human body and is quickly destroyed, it can be combined with certain binding proteins to extend the half-life, but it is not a very simple procedure and there is a more effective and less expensive version available. The most effective form of IGF is Long R3 IGF-1, it has been chemically altered and has had amino acid changes which cause it to avoid binding to proteins in the human body and allow it to have a much longer half life, around 20-30 hours. "Long R3 IGF-1 is an 83 amino acid analog of IGF-1 comprising the complete human IGF-1 sequence with the substition of an Arg? for the Glu(E) at position three, hence R3, and a 13 amino acid extension peptide at the N terminus. This analog of IGF-1 has been produced with the purpose of increasing the biological activity of the IGF peptide."
"Long R3 IGF-1 is signifacantly more potent than IGF-1. The enhanced potency is due to the decreased binding of Long R3 IGF-1 to all known IGF binding proteins. These binding proteins normally inhibit the biological actions of IGF's."