Researchers can't fully explain why IGF LR3 outperforms its natural counterpart in preclinical models. Engineered in the 1990s with an arginine substitution and N terminal extension, this synthetic IGF 1 analog shows reduced IGFBP binding LONG R IGF I Mechanisms of IGF 1 Mediated Regulation of Skeletal Muscle Hypertrophy and Atrophy A Medical Review of IGF 1 LR3 Dosage, Side Effects and Safety Aspects