Two Growth Factors, Two Mechanisms
IGF-1 LR3 and PEG-MGF (PEGylated Mechano Growth Factor) are both derivatives of insulin-like growth factor 1, but they operate through fundamentally different anabolic mechanisms and produce distinct physiological outcomes.
IGF-1 LR3 is a systemic growth factor with a 20-30 hour half-life that drives both hypertrophy (fiber enlargement) and hyperplasia (new fiber creation) through satellite cell activation at the IGF-1 receptor. It circulates systemically and affects all tissues with IGF-1R expression.
PEG-MGF (PEGylated IGF-1Ec splice variant) is a mechano-sensitive growth factor that is specifically upregulated in response to mechanical damage - the microtears caused by resistance training. PEGylation extends its half-life from minutes to several days. MGF's primary role is recruiting dormant satellite cells to damaged muscle fibers for repair and fusion.
When to Use Each
IGF-1 LR3 for systemic anabolism: use during bulking phases when the goal is overall tissue growth. Dose: 20-60 mcg/day subcutaneously for 4-6 weeks. Best administered post-workout or pre-bed.
PEG-MGF for localized muscle repair: use immediately post-workout via intramuscular injection into the trained muscle group. Dose: 200-400 mcg bilaterally into worked muscles, 2-3 times per week. The localized injection targets satellite cell activation at the site of mechanical damage.
Sequential protocol: some advanced protocols run PEG-MGF during training sessions (immediately post-workout, IM) for localized satellite cell activation, followed by IGF-1 LR3 on rest days (subcutaneously) for systemic growth factor support. Do not inject both on the same day - IGF-1 LR3 can compete with MGF for receptor binding and reduce the localized effect.
Key Differences Summary
Half-life: IGF-1 LR3 ~20-30 hours, PEG-MGF ~several days (unpegylated MGF is minutes).
Administration: IGF-1 LR3 subcutaneous (systemic), PEG-MGF intramuscular (localized to trained muscle).
Primary action: IGF-1 LR3 activates proliferating satellite cells and drives them to differentiate into myoblasts. PEG-MGF recruits quiescent satellite cells from their niche and activates them - it initiates the repair cascade that IGF-1 LR3 then amplifies.
Cycle length: IGF-1 LR3 max 4-6 weeks (suppresses endogenous IGF-1). PEG-MGF can be used for longer cycles (8-12 weeks) without significant axis suppression since its mechanism is mechano-dependent rather than systemic.
