IGF-1 LR3: How Insulin-Like Growth Factor Builds Muscle
IGF-1 LR3 works downstream of HGH to stimulate satellite cell proliferation and hyperplasia — actual new muscle fibres, not just hypertrophy. We cover mechanisms, dosing protocols, and what to realistically expect.
The GH → IGF-1 Axis
Growth hormone does not directly build muscle. GH travels to the liver, which converts it into IGF-1 (Insulin-like Growth Factor 1). IGF-1 is the primary mediator of most anabolic effects attributed to GH: protein synthesis, satellite cell activation, bone growth, and fat lipolysis. Endogenous IGF-1 has a very short half-life (~12–15 minutes) due to binding protein degradation. IGF-1 LR3 (Long R3) is a modified analogue with a substitution at position 3 (Arg→Glu) that prevents IGFBP-3 binding, extending its half-life to 20–30 hours.
Hyperplasia vs Hypertrophy
Standard training and most anabolic compounds cause hypertrophy — existing muscle fibres get larger. IGF-1 is one of the few compounds capable of stimulating hyperplasia — the creation of new muscle fibres — by activating and proliferating satellite cells (muscle stem cells). This is why experienced athletes who have maxed out hypertrophic potential find IGF-1 uniquely effective: it adds new fibres rather than just enlarging existing ones. The new fibres are permanent — unlike hypertrophy gains that require maintenance training.
Dosing Protocol
IGF-1 LR3 dose: 40–100 mcg/day. Injection: subcutaneous or intramuscular. Timing: post-workout, injected directly into the trained muscle group (site-specific growth is theorised due to local IGF-1 receptor activation). Cycle length: 4–6 weeks, followed by a break of equal duration (receptor downregulation occurs with longer use). Reconstitute with bacteriostatic water; store refrigerated; stable for 20–30 days once reconstituted. Note: IGF-1 drives cellular growth non-selectively — avoid if there is any history of cancer or pre-cancerous conditions.
Synergistic Stacking
IGF-1 LR3 is most effective when combined with HGH peptides (GHRP/CJC stack) and anabolic steroids. GH peptides raise endogenous IGF-1; exogenous IGF-1 LR3 saturates peripheral IGF-1 receptors directly. The combination produces both hepatic IGF-1 elevation and local tissue IGF-1 availability. Combined with testosterone, the anabolic signalling cascade is maximally activated across all three axes: androgen receptor, GH receptor, and IGF-1 receptor.
Realistic Results and Side Effects
Realistic expectation on a 6-week IGF-1 LR3 cycle (50 mcg/day) with a caloric surplus: 2–4 kg of lean mass, notably enhanced muscle fullness and density. Side effects: hypoglycaemia (IGF-1 has insulin-like activity — inject post-workout when glycogen is depleted and have carbohydrates ready), lethargy, tingling in extremities. Organ growth (colloquially "GH gut") is associated with multi-year supraphysiological GH and IGF-1 elevation — not typical 6-week cycles. Jaw, hand, or foot growth (acromegaly) requires extremely long-term high-dose use.
Written by
Sofia Brenner
Certified Strength & Conditioning Coach