The IGF-1 splice variant produced by mechanically loaded muscle — MGF for post-workout local action, PEG-MGF for twice-weekly systemic dosing.
Mechano Growth Factor (MGF) is a splice variant of IGF-1 — IGF-1Ec in humans, IGF-1Eb in rodents — produced locally by skeletal muscle in response to mechanical loading. A 49-base-pair insert shifts the reading frame and yields a 24-amino-acid C-terminal E-domain peptide that native IGF-1 does not have. The compound sold as “MGF” is that E-domain peptide on its own, not the full-length splice variant — a distinction that turns out to matter enormously (see the evidence section below).
The splicing itself is well established: Hill and Goldspink (J Physiol 2003, PMID 12692175) showed the gene is spliced toward this variant after local muscle damage, and Goldspink 2005 (PMID 16024511) laid out the mechanical-signalling model.
Native MGF has a serum half-life of roughly 5 to 7 minutes. Endogenously that is not a problem, because the muscle makes it exactly where it is needed. Injected, it is the central practical obstacle, and the reason PEG-MGF exists — a polyethylene-glycol-conjugated form said to last far longer, though the commonly quoted 48–72 hour figure is a community number rather than a published human PK result.
Not FDA approved. WADA prohibited (S2). Research chemical only.
MGF’s E-domain activates quiescent satellite cells lining muscle fibers, driving their proliferation and fusion into existing fibers — the cellular mechanism behind hypertrophy and repair.
MGF is produced at the site of mechanical load and acts locally. That is the whole premise, and it is the reason protocols specify intramuscular injection into the muscle you just trained rather than a convenient subcutaneous site: the intent is to place the peptide where the damage is, because systemic delivery of a short-lived local factor has no obvious way to concentrate there.
Be honest about how weak the delivery model is either way. Researchers who wanted sustained local MGF did not inject it — they engineered a hydrogel microrod device to elute it over two weeks, precisely because free peptide does not persist (PMID 24908137). Between that and the cDNA gene-delivery used in the animal work, almost no published study has done what users do: inject free MGF peptide as a bolus. PEG-MGF exists to extend exposure, which helps with persistence but works against the locality the mechanism depends on.
MGF shares the IGF-1 core sequence, but the E-domain peptide does not act through the IGF-1 receptor. Janssen 2016 (PMID 26991004) tested this directly with receptor-activation bioassays: full-length MGF activated the IGF-1 receptor about as strongly as IGF-I at high concentrations, though roughly nine times less potently (EC50 7.83 vs 0.86 nmol/L) — while human MGF E-peptide and the stabilised Goldspink-MGF analogue produced no IGF-1 receptor activation at any concentration tested.
Older material, this guide included, used to say the E-domain binds “a distinct receptor on satellite cells.” That overstates what is known. No receptor for the E-domain peptide has been identified. If it acts, it acts through a pathway nobody has characterised yet.
| Benefit | Evidence |
|---|---|
| Muscle repair | Rat studies: MGF accelerates recovery from injury via satellite-cell proliferation |
| Hypertrophy | Post-workout injection combined with resistance training shows satellite-cell proliferation in animal models |
| Cardiac repair | Preclinical data on post-MI tissue regeneration — independent research interest |
| Neuroprotection | Some evidence for nerve-cell survival after ischemia |
Human data are limited. The rationale is strong mechanistically, but well-controlled human trials haven’t validated the anecdotal bodybuilding results.
Build your protocol, log every dose, monitor your body's response, and get reminders so you never miss a dose.
Start Tracking FreeMGF is the one compound in this category where the central question is not “how well does it work” but “does the injectable version do anything at all.” That question is unresolved in the published literature, and anyone considering MGF should know it before anything else.
Kandalla 2011 (PMID 21354439) applied MGF-24aa-E peptide to human muscle progenitor cells and found increased proliferative lifespan, delayed senescence and greater fusion potential, with weaker effects in cells from older donors. This is the most-cited support for the muscle claim. It is an in vitro study on cell cultures.
Outside muscle the E-domain has produced repeated positive results: neuroprotection in gerbil brain ischaemia, outlasting full-length IGF-1 and working independently of the IGF-1 receptor (Dluzniewska 2005, PMID 16144956); neurogenesis in the ageing mouse brain (Tang 2017, PMID 28683812); preserved cardiac function after infarction in sheep (Carpenter 2008, PMID 17581790) and in mice via blocked apoptosis (Mavrommatis 2013, PMID 23712705), with localised polymer delivery improving on that again (Peña 2015, PMID 25678113); and a role in chondrocytes and cartilage repair (Liu 2023, PMID 37171185).
Fornaro 2014 (PMID 24253050) is the study that broke the consensus. Researchers at two pharmaceutical companies set out specifically to reproduce MGF's claimed muscle effects. At peptide concentrations up to 500 ng/mL, MGF failed to increase proliferation of C2C12 cells, primary human skeletal muscle myoblasts, or primary mouse muscle stem cells — while mature IGF-1 and full-length IGF-1Eb produced a response in all of them. MGF also failed to delay myoblast differentiation, and failed to activate p-ERK in cardiac myocytes, which is the very signalling step usually offered as its mechanism. Their conclusion: the results "call in to question whether there is a physiological role for MGF."
Janssen 2016 (PMID 26991004) added the receptor half: no IGF-1 receptor activation from the E-peptide at any concentration, as described above.
And there is a deeper problem than efficacy. Matheny 2010 (PMID 20130113) and Zabłocka 2012 (PMID 23125840) both point out that no endogenous E-peptide product has ever been conclusively isolated from cells or tissue. The gene splices; whether the body actually liberates and uses a free 24-amino-acid peptide is unconfirmed. Zabłocka's title puts it plainly — an important cog, or a loose screw.
The splicing biology is real and well documented. The synthetic E-domain peptide has real, reproducible effects in neural and cardiac tissue. What has failed replication is specifically the muscle claim — the reason almost everyone buys it. That asymmetry is the honest summary, and it is not what the marketing says.
Community reports are consistent with a weak or absent effect: mixed at best, frequently described as underwhelming relative to a protocol that demands an intramuscular injection into the muscle you just trained, inside a window of minutes.
Not medical advice. These figures describe what is reported in the literature and what practitioners and communities do — not a recommendation, and for most compounds here no human dose-finding study exists. Talk to a qualified healthcare provider.
Animal work delivered MGF mostly as cDNA (gene delivery), not injected peptide, which makes translation to a microgram dose impossible. In vitro work used 50–500 ng/mL in culture — a concentration, not a dose. Where researchers wanted sustained local delivery they built a device to elute it (PMID 24908137) rather than injecting it. There is no dose-finding study for injected MGF peptide in humans, and no human trial of any kind. The protocols below are community convention, and the fact that two widely repeated conventions differ two-fold is a fair measure of how little anchors them.
Two conventions circulate: 100–200 mcg and 200–400 mcg. They overlap at 200 mcg, which is where most protocols land and the most defensible place to sit given that neither end rests on anything published. Subcutaneous dosing is common and simpler, but it gives up the locality that is the entire rationale for the compound — if you are not injecting into the trained muscle, be clear that you are choosing convenience over the mechanism.
PEG-MGF is more practical for non-training days and for users who can’t dose post-workout.
Pre-filled with a typical MGF and PEG-MGF setup. Edit any field — the draw updates live.
Insulin syringe — 100 units = 1 mL
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Not medical advice. These figures describe what is reported in the literature and what practitioners and communities do — not a recommendation, and for most compounds here no human dose-finding study exists. Talk to a qualified healthcare provider.
2 mg vial + 2 mL BAC water = 1000 mcg/mL
| Dose | Volume | Syringe Units |
|---|---|---|
| 100 mcg | 0.10 mL | 10 units |
| 200 mcg | 0.20 mL | 20 units |
| 250 mcg | 0.25 mL | 25 units |
Satellite-cell activation and pro-survival signalling do not distinguish between tissue you want to grow and tissue you do not. Any cancer history is an absolute contraindication. Add inflammatory bowel disease to the caution list on the strength of the stricture finding above.
MGF and PEG-MGF is a research peptide not approved by the FDA for human use. It is sold only as a research chemical, and StackTrax does not endorse or facilitate personal use.
Quality varies enormously among research-chemical suppliers. At minimum, look for:
Lyvn does not carry MGF and PEG-MGF. They are the vendor we recommend elsewhere on this site, and they publish the full independent panel per batch — which makes their catalogue a useful yardstick for the criteria above even on a compound they do not stock. We are not recommending a specific supplier for MGF and PEG-MGF itself, because we have no basis to.
For research use only. Not for human consumption. 21+.
Build your protocol, log every dose, monitor your body's response, and get reminders so you never miss a dose.
Start Tracking FreeNo. MGF (mechano growth factor — the synthetic 24-amino-acid E-peptide derived from the IGF-1Ec splice variant) has never been FDA, EMA, or any other regulatory authority approved. The endogenous splice variant is a real biological molecule, but its synthetic E-peptide bioactivity and the existence of a dedicated MGF receptor are scientifically contested. Sold in the US only as a research chemical.
Community-practice dosing is 100–200 mcg post-workout, injected intramuscularly directly into the trained muscle. This is bodybuilding-forum convention — no peer-reviewed human dose-finding study for MGF E-peptide hypertrophy exists. The "5–7 minute half-life" widely cited for MGF is also not anchored to a peer-reviewed human PK study.
A typical reconstitution is 2 mg of MGF + 1 mL of bacteriostatic water, yielding 2 mg/mL (2000 mcg/mL). A 100 mcg dose draws to 0.05 mL (5 units on a 100-unit insulin syringe), 200 mcg = 0.10 mL (10 units).
MGF (the synthetic 24-aa E-peptide) has a very short reported half-life of ~5–7 minutes — the rationale for community injection-into-trained-muscle protocols (high local exposure, minimal systemic). PEG-MGF adds a polyethylene glycol modification, claimed to extend half-life to 48–72 hours for systemic dosing. Both half-life numbers are vendor/community-tier claims, not anchored to peer-reviewed human PK studies of either molecule.
The endogenous IGF-1Ec splice variant is upregulated by mechanical loading and has documented effects in animal muscle satellite cell activation. Whether the synthetic 24-aa E-peptide reproduces that activity is contested in the peer-reviewed literature — the Goldspink, Kandalla, and Fornaro groups have disagreed about reproducibility. There are no human RCTs of synthetic MGF for hypertrophy.
Yes. WADA explicitly names "mechano growth factors (MGFs)" in S2.3 (Growth Factors and Growth Factor Modulators). Prohibited at all times. No therapeutic-use exemption available.
Disclaimer: This guide is for educational and informational purposes only and is not intended as medical advice, diagnosis, or treatment. The compounds discussed are not FDA approved for human use. Always consult a qualified healthcare provider before starting any new supplement or peptide protocol. StackTrax does not sell peptides or supplements directly — purchase links go to third-party vendors. StackTrax is not responsible for the products, quality, or business practices of any third-party vendor.
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StackTrax guides cover peptides and compounds that are not FDA-approved for the uses discussed. The dosing, reconstitution, and safety information is compiled from published research and community protocols for educational purposes only.
Before using any compound mentioned here, consult a qualified healthcare provider. StackTrax does not sell, prescribe, or recommend these substances for personal use.