Compounds / GH secretagogues

MGF

Mechano Growth Factor (IGF-1Ec splice variant: IGF-1 with E-domain peptide tail)

Splice variant of the IGF-1 gene (IGF-1Ec in humans, IGF-1Eb in rodents) discovered by Geoffrey Goldspink's lab in the early 2000s. Produced locally in skeletal muscle in response to mechanical loading and injury. The unique C-terminal E-domain peptide is thought to drive satellite cell activation and proliferation independently of the IGF-1 receptor. Bodybuilders inject the synthetic E-domain peptide locally into muscle for site-specific hypertrophy. Half-life is minutes (extremely rapid proteolysis). Most users find unmodified MGF underwhelming and migrate to PEG-MGF (PEGylated form, separate compound) for any systemic or sustained effect.

At a glance

Half-life

~6 min Plasma t½ ~5-7 minutes. Extremely rapid proteolysis. PEG-MGF (PEGylated form) extends t½ to ~48-72 hours and is the more practical commercial form.

Routes

IM · SubQ

Vial sizes

2 mg · 5 mg

Evidence base

3 studies 1 review · 2 preclinical

Mechanism

In response to mechanical loading or injury, the IGF-1 gene is alternatively spliced to produce IGF-1Ec, which is then cleaved to release the mature IGF-1 portion plus a unique E-domain peptide ('MGF'). The E-domain is thought to bind a distinct (still uncharacterized) receptor that triggers satellite cell activation and proliferation, distinct from IGF-1 receptor signaling, which drives differentiation. The bodybuilding peptide product is the synthetic E-domain peptide alone (24aa), injected locally to recruit satellite cells to the trained muscle for hypertrophy.

Dosing

Published evidence

1. Review 2005

   Mechanical signals, IGF-I gene splicing, and muscle adaptation

   Goldspink G Physiology

   Foundational review: established MGF's role as a local muscle adaptation peptide distinct from systemic IGF-1.

   PMID 15985543

2. Animal in vivo 2003

   Expression and splicing of the insulin-like growth factor gene in rodent muscle is associated with muscle satellite (stem) cell activation following local tissue damage

   Hill M, Goldspink G J Physiol

   Established mechanistic link between MGF expression and satellite cell activation in damaged muscle: basis for hypertrophy claims.

   PMID 12651923

3. Animal in vivo 1996

   Cloning and characterization of an IGF-1 isoform expressed in skeletal muscle subjected to stretch

   Yang S, Alnaqeeb M, Simpson H, Goldspink G J Muscle Res Cell Motil

   Original cloning of stretch-induced IGF-1 splice variant (IGF-1Ec / MGF): established existence of the local muscle splice variant.

   PMID 8884603

Reported side effects

Injection site reaction

Common Mild · IM injection causes local soreness; some report transient muscle tightness.

Localized swelling / pump

Common Mild · Often considered desirable: local trophic response.

Theoretical mitogenic effect

Unknown Moderate · Less established than IGF-1 cancer concern (E-domain peptide has different signaling), but caution warranted with chronic high-dose local exposure.

Lack of effect (unmodified MGF)

Common Mild · Half-life so short that many users report no detectable difference. PEG-MGF is more popular for this reason.

Interactions

• IGF-1 LR3 Synergy

  Sequential satellite cell activation (MGF) → differentiation/protein synthesis (IGF-1). Common bodybuilding stack: MGF post-workout, IGF-1 LR3 between training days.

• Test Cypionate Synergy

  Anabolic synergy. Common stack.

Reconstitution and storage

2mg vial + 1mL BAC water → 2000 mcg/mL. 0.1mL = 200 mcg. Reconstituted MGF degrades fast. Many users reconstitute immediately before injection.

Lyophilized at -20°C. Reconstituted refrigerated, use within 7 days (faster degradation than other peptides). Many users prefer single-use reconstitution.

Open the reconstitution calculator for MGF