Editorial note: this article summarises published research on mechano growth factor. Baclabs does not sell MGF, PEG-MGF or any peptide; we supply bacteriostatic water and reconstitution consumables. Nothing here is medical advice.
MGF, mechano growth factor, is the E-domain of the IGF-1Ec splice variant, a form of insulin-like growth factor 1 that skeletal muscle upregulates after mechanical loading and damage. PEG-MGF is the same peptide with a polyethylene glycol chain attached to slow its clearance. The marketing story is that MGF activates satellite cells to repair and add myonuclei to damaged fibres, and that PEG-MGF does so for longer.
The biology behind that story is genuine and interesting. The evidence that injecting the synthetic peptide reproduces it is not. Two well-conducted studies published in 2014 and 2016 found either no effect on muscle cells at all or no activation of the IGF-1 receptor by the synthetic E-peptide, which is a meaningful problem for the entire premise.
Where mechano growth factor came from
The IGF-1 gene produces several transcripts through alternative splicing. In addition to the systemic IGF-1Ea isoform, loaded or damaged muscle upregulates IGF-1Ec, which carries a distinct C-terminal E-domain. Geoffrey Goldspink’s group at the Royal Free in London characterised this isoform in stretched and electrically stimulated rabbit muscle in the 1990s and named it mechano growth factor, proposing that the E-domain, after cleavage from the mature IGF-1 portion, acts as a separate signalling molecule that pushes satellite cells to proliferate before they differentiate.
Satellite cells matter because adult muscle fibres are post-mitotic. To grow substantially or repair serious damage, a fibre needs new myonuclei, and those come from satellite cells that proliferate, then fuse into the fibre. A molecule that specifically expands the proliferating pool before differentiation begins would be useful. That is the hypothesis MGF products are sold on.
What the direct evidence on the peptide shows
Supportive results exist in the wider literature. MGF has been reported to promote proliferation and inhibit differentiation of porcine satellite cells by downregulating key myogenic transcription factors [7], and E-domain peptides have been studied in tendon healing, bone defect repair, cardiac protection and neurogenesis models. Those are mostly animal or cell-based studies in tissues other than trained human skeletal muscle.
Two studies cut against the core claim.
Fornaro and colleagues, publishing in the American Journal of Physiology, Endocrinology and Metabolism in 2014, tested the MGF peptide, the COOH terminus of unprocessed IGF-1, on myoblasts and primary muscle stem cells and reported no apparent effect [1][2]. The title states the finding plainly.
Janssen and colleagues, in PLOS ONE in 2016, compared full-length MGF with recombinant human IGF-1 for IGF-1 receptor activation. Full-length MGF reached a similar maximum stimulation to IGF-1 (89-fold versus 77-fold) but needed roughly nine times more of it to get there (EC50 7.83 versus 0.86 nmol/L). Critically, the synthetic E-peptides they tested, including a Goldspink-MGF construct, produced no IGF-1 receptor activation whatsoever [3].
So the intact IGF-1Ec protein does signal, less potently than IGF-1. The isolated E-domain peptide, which is what is sold as MGF, did not. No receptor has been definitively identified for the E-peptide, which is a substantial unresolved gap.
MGF vs PEG-MGF: what pegylation changes
Pegylation, covalently attaching polyethylene glycol, increases hydrodynamic radius, reduces renal filtration and shields the molecule from proteases. It is a well-established technique used in licensed medicines such as pegfilgrastim and peginterferon. In principle it converts a peptide with a very short circulating life into one lasting hours or days.
Applied to MGF, the claim is that unmodified MGF survives only a few minutes in circulation and therefore has to be injected close to the trained muscle immediately after training, whereas PEG-MGF persists long enough for systemic dosing every few days.
We could not locate any published human pharmacokinetic study, controlled trial or registry entry for PEG-MGF. The pegylation chemistry is well characterised in general; the specific pegylated MGF product is not characterised anywhere we could find in the peer-reviewed literature. The half-life figures quoted by vendors (commonly “a few minutes” for MGF and “two to three days” for PEG-MGF) have no traceable source. Pegylation also changes tissue distribution and immunogenicity, neither of which has been assessed for this molecule.
| MGF (E-domain peptide) | PEG-MGF | |
|---|---|---|
| Structure | C-terminal E-domain of IGF-1Ec | Same peptide plus a PEG chain |
| IGF-1 receptor activation | Not observed for synthetic E-peptides [3] | Not tested in any published study located |
| Effect on myoblasts/muscle stem cells | No apparent effect in Fornaro et al. [1] | Not tested in any published study located |
| Published human PK | None located | None located |
| WADA status | Prohibited at all times, S2 [4][6] | Prohibited at all times, S2 [4][6] |
PEG-MGF post workout timing: what can and cannot be said
“PEG-MGF post workout timing” is a common search, and the honest answer is that the timing question cannot be resolved because the prior question, does the peptide do anything in human muscle, has not been answered.
The rationale offered is that mechanical loading transiently upregulates endogenous IGF-1Ec, so exogenous MGF given into or near the worked muscle within an hour or two of training should amplify a window that is already open. Community protocols typically describe 200–400 mcg of PEG-MGF once or twice weekly, or 100–200 mcg of unmodified MGF injected near the trained muscle immediately post-session. These are unattributed forum and vendor figures. No dose-finding study, no controlled trial and no pharmacokinetic dataset generated them, and there is no published human safety information at any exposure.
It is also worth noting that the endogenous splicing response is a local, transcriptionally driven event inside loaded fibres. Injecting a peptide into the interstitial space is not obviously equivalent to that, even if the peptide were active.
Safety, regulation and detection
Because no human study exists, the adverse effect profile of MGF and PEG-MGF is unknown rather than reassuring. Plausible concerns follow from the family it belongs to: any compound with meaningful IGF-1 receptor activity carries hypoglycaemia and mitogenic considerations, and any pegylated protein carries a theoretical immunogenicity and PEG-accumulation question. None of this has been measured for these products.
Neither MGF nor PEG-MGF holds a UK marketing authorisation. Supply for human use falls under the Human Medicines Regulations 2012 and MHRA enforcement. In sport, mechano growth factors are named explicitly in WADA section S2, prohibited at all times as non-specified substances [4][6], and mass spectrometric methods for detecting biotechnologically produced full-length MGF in doping control samples have been published [5].
Reconstitution and diluent choice
MGF and PEG-MGF are supplied lyophilised. Peptides in this family are handled gently: add diluent slowly down the vial wall, swirl rather than shake, and keep reconstituted vials refrigerated and out of light. A multi-dose vial needs a preserved diluent, because each puncture is a chance to introduce organisms into a solution that will sit for weeks. Baclabs supplies UK-stocked bacteriostatic water in 30 mL vials; the reconstitution guide sets out the concentration maths, bacteriostatic vs sterile water covers diluent selection, and storage and shelf life explains the 28-day in-use limit.
For how MGF relates to the wider class, see the muscle growth peptides hub; for the engineered IGF-1 analogues it is often stacked with in marketing material, see IGF-1 LR3 vs IGF-1 DES.
Frequently asked questions
What is MGF and how is it different from IGF-1?
MGF is the C-terminal E-domain of IGF-1Ec, a splice variant of the IGF-1 gene that muscle upregulates after mechanical loading. IGF-1 proper is the mature growth factor that binds the IGF-1 receptor. In one study, full-length MGF activated that receptor with about nine-fold lower potency than IGF-1, while isolated synthetic E-peptides did not activate it at all [3].
Is PEG-MGF better than MGF?
No comparison has been published. Pegylation reliably extends the circulating life of proteins in general, but no human pharmacokinetic study of PEG-MGF appears to exist, and the underlying peptide’s activity on muscle cells is itself disputed [1][3]. A longer half-life for an inactive molecule is not an advantage.
What is the best PEG-MGF post workout timing?
There is no evidence-based answer. Community protocols suggest injection within an hour or two of training, on the theory that endogenous IGF-1Ec upregulation opens a window. Those timings and the accompanying 200–400 mcg weekly figures are unattributed claims with no trial, dose-finding study or pharmacokinetic dataset behind them.
Does MGF activate satellite cells?
Some cell and animal work supports the idea, including reports that MGF promotes satellite cell proliferation while inhibiting differentiation. But Fornaro and colleagues found the MGF peptide had no apparent effect on myoblasts or primary muscle stem cells [1], and no controlled human study exists. The question is unresolved.
Is MGF banned in sport?
Yes. Mechano growth factors are listed by name in WADA section S2 alongside growth hormone and IGF-1 analogues, prohibited at all times and classed as non-specified substances [4][6]. Analytical methods for detecting full-length MGF have been published in the doping control literature [5].
References
- Fornaro M et al. Mechano-growth factor peptide, the COOH terminus of unprocessed insulin-like growth factor 1, has no apparent effect on myoblasts or primary muscle stem cells. American Journal of Physiology, Endocrinology and Metabolism, 2014
- Same article, publisher full text. American Physiological Society, 2014
- Janssen JAMJL et al. Potency of full-length MGF to induce maximal activation of the IGF-I R is similar to recombinant human IGF-I at high equimolar concentrations. PLOS ONE, 2016
- WADA Prohibited List S2: Peptide hormones, growth factors, related substances and mimetics. Drugs.com summary of the WADA list
- Mass spectrometric characterization of a biotechnologically produced full-length mechano growth factor (MGF) relevant for doping controls. Growth Hormone & IGF Research, 2014
- The Prohibited List. World Anti-Doping Agency
- Mechano growth factor (MGF) promotes proliferation and inhibits differentiation of porcine satellite cells (PSCs) by down-regulation of key myogenic transcriptional factors. Molecular and Cellular Biochemistry, 2012
Disclaimer: This content is for educational purposes only and does not constitute medical advice. Bacteriostatic water is supplied for reconstitution of substances intended for research and for use as directed by a healthcare professional. Peptides and medicines discussed here may be unlicensed in the UK or prescription-only; consult a qualified clinician before using any medicine. Baclabs does not sell peptides.