Source comparison
IGF-1 LR3 vs Endogenous IGF-1 and Alternative Growth Factors
IGF-1 LR3 20–30 hours Minimal (modified E-domain) High (direct IGF-1R agonism) 20–80mcg daily Receptor saturation above 60mcg Endogenous IGF-1 10–12 minutes >95% bound in circulation Low (limited bioavailability) N/A (endogenous) Sequestered by IGFBPs. Minimal
This comparison does not assign a generated winner or score.
- IGF-1 LR3
- 20–30 hours
- Minimal (modified E-domain)
- High (direct IGF-1R agonism)
- 20–80mcg daily
- Receptor saturation above 60mcg
- Endogenous IGF-1
- 10–12 minutes
- >95% bound in circulation
- Low (limited bioavailability)
- N/A (endogenous)
- Sequestered by IGFBPs. Minimal free fraction
- MK-677 (Ibutamoren)
- 4–6 hours
- Indirect (increases endogenous IGF-1)
- Moderate (systemic IGF-1 elevation)
- 10–25mg daily
- Elevates cortisol and prolactin; slower onset
- Mechano Growth Factor (MGF)
- <10 minutes
- Minimal
- Very high (splice variant specific to muscle)
- 100–200mcg post-training
- Extremely short half-life limits sustained activation
- HGH (Somatropin)
- 2.5–3 hours
- Indirect (hepatic IGF-1 synthesis)
- Low (broad systemic effects)
- 2–4 IU daily
- Cost; systemic side effects; delayed IGF-1 response
- The key advantage of IGF-1 LR3 over endogenous IGF-1 is bioavailability. More than 95% of circulating IGF-1 in the body is bound to IGF binding proteins (primarily IGFBP-3), which prevent the peptide from reaching target receptors. IGF-1 LR3's amino acid substitution at position 3 (glutamic acid replacing the standard amino acid) reduces IGFBP affinity by more than 90%, allowing the peptide to remain in free, bioavailable form. This is why IGF-1 LR3 at 40mcg produces stronger satellite cell activation than endogenous IGF-1 levels 10× higher. The structural modification bypasses the body's regulatory sequestration mechanism.
- MK-677 offers an alternative approach by stimulating endogenous growth hormone release, which then triggers hepatic IGF-1 synthesis. The mechanism is indirect and slower. Peak IGF-1 elevation occurs 4–6 hours post-administration vs immediate receptor activation with exogenous IGF-1 LR3. For researchers prioritizing sustained elevation of baseline IGF-1 across multiple tissue types, MK-677 provides systemic coverage. For targeted satellite cell research with rapid onset, IGF-1 LR3 remains the superior choice.