PerformanceMechano-Growth FactorIGF-1 Ec

MGF

Mechano-Growth Factor · 24-AA IGF-1 Ec splice-variant E-domain peptide

MGF (Mechano-Growth Factor) is a peptide based on a natural splice variant of the IGF-1 gene that appears in muscle after mechanical overload. The research peptide is just the short, unique tail (the "E-domain") of that variant, and it was proposed to act as a separate local repair and stem-cell-activation signal — distinct from regular IGF-1. That proposal is genuinely contested: a key independent study found the synthetic peptide had no unique activity, no free natural version of it has ever been isolated from tissue, and its receptor is unknown. It is a research reagent with no approved human use, no human trials, and is prohibited in sport (WADA).

The short version

MGF stands for Mechano-Growth Factor. When a muscle is loaded hard, the body briefly reads the IGF-1 gene in a different way, producing a special variant. MGF the peptide is the short, distinctive tail of that variant — and the idea is that this tail acts as its own "go repair this" signal, separate from the steady growth signal of ordinary IGF-1.

That idea is where the honesty matters. The original research group proposed MGF kick-starts muscle repair by waking up satellite cells (the muscle's local stem cells). But an independent lab later found the lab-made peptide did nothing unique, scientists have never actually isolated this free tail from real tissue, and nobody has identified what receptor it would even act on. So the headline mechanism is a hypothesis, not a settled fact.

It is sold as a research reagent, not a medicine. There are no human trials, it is not an approved drug, and it is banned in competitive sport.

Molecular identity

Specs

Molecular weight: 2,868.1 g/mol
Molecular formula: C121H199N41O40
Monoisotopic mass: 2,866.48 Da

Sequence (24 AA): YQPPSTNKNTKSQRRKGSTFEERKPubChem CID 175675731
Structure / class: Synthetic C-terminal E-domain peptide of the IGF-1Ec splice variant (human mechano-growth factor)PMID 20130113
CAS number: No single reliable CAS registry numberNot established
Physical form: Lyophilized powder; a Cys-tagged 25-mer variant is sold separately for conjugationResearch literature
Molecular target: Proposed distinct (still-unidentified) receptor — NOT confirmed; unique activity not replicated independentlyPMID 24253050
Half-life: Not established (reported very short; no primary source)Not established
Regulatory status: Research reagent; not FDA-approved; prohibited in sport (WADA S2, growth factors; mechano growth factors named)WADA Prohibited List

Plain English

Mechanism

The proposed story goes like this. The IGF-1 gene can be read ("spliced") in more than one way. After mechanical overload — hard or damaging exercise — muscle briefly favors a variant called IGF-1Ec in humans, whose extra tail is the "E-domain." Goldspink's group proposed that this E-domain, on its own, is a distinct early signal that activates satellite cells (muscle stem cells) and protects muscle fibers, kicking off repair before the slower, mainstream IGF-1 takes over to finish the job.

Crucially, MGF was proposed to do this through a different, still-unidentified receptor — not the normal IGF-1 receptor — which is why it was framed as a separate tool rather than just more IGF-1.

Here is the honest counterweight, and it is substantial. An independent study found the synthetic E-domain peptide had no unique biological activity of its own (it behaved like an inert fragment), no one has ever isolated a free, standalone 24-amino-acid MGF peptide from living tissue, and the supposed dedicated receptor has never been identified. So the mechanism above should be read as an unproven hypothesis with meaningful evidence against it — not as how MGF is known to work.

Sources:PMID 16244184 PMID 24253050 PMID 20130113

Why people reach for it

Potential benefits

MGF is reached for as a local, post-workout repair signal — but its headline mechanism is genuinely contested, so its appeal is best read as a hypothesis people are testing, not a proven effect.

A proposed jump-start for muscle repair — Its central draw. In the originating group's model, the MGF E-domain wakes up satellite cells (the muscle's local stem cells) after mechanical damage — the early signal that's proposed to kick off repair before mainstream IGF-1 takes over.
Timed to the post-workout damage window — Because the natural variant appears in muscle right after hard loading, people inject it post-training to mimic that pulse — the timing is the whole point of how it's used.
Used as a site-targeted local pulse — Reported to be very short-lived, so it's injected into or near the worked muscle for a brief, local effect rather than a systemic one — which is exactly the niche people reach for it to fill.
A front-end primer for a proliferation signal — Most coherently stacked ahead of IGF-1 DES or IGF-1 LR3 — MGF proposed to activate satellite cells, the IGF variant to drive their proliferation in the same window.
Honest caveat: the effect may not be real — An independent study found the synthetic peptide had no unique activity, no free natural version has been isolated from tissue, and its receptor is unknown — so this is a compound people experiment with, not one with established benefits.

Sources:PMID 16244184 PMID 20130113 PMID 24253050

What people reach for MGF for, drawn from a contested hypothesis (with meaningful evidence against it) and how it's used — not proven outcomes or medical claims.

Implied timing

Best time to dose

Implied best time

Immediately post-workout (local)

Most people inject MGF into the worked muscle immediately after training — inside the mechanical-damage window the compound is proposed to amplify.

MGF is the splice variant the body is proposed to release after mechanical damage, so dosing right after training is meant to mimic that natural post-exercise pulse — the timing follows directly from the (contested) mechanism, not from a clock-based schedule.
It's reported to be very short-lived (degraded rapidly without PEGylation), so the window is kept tight: injected within roughly 30–60 minutes post-workout, into or near the muscle just trained, for a local effect.
Pre-workout use has no supporting logic in the overload framework — there's no mechanical-damage signal yet for it to amplify — so it's tied to the session after the work is done.
On non-training days there's no damage event to act on, so MGF isn't dosed then; the timing is entirely event-driven, set by the workout.

No study establishes an ideal time of day for MGF — this is reasoned from its proposed post-damage mechanism and how it's used. Most peptide dosing lands in the midday-to-evening window; for MGF the anchor is immediately after the training session, not the time of day.

Sources:PMID 16244184 PMID 20130113

How to run it

Dosing & protocol

MGF is used as a site-targeted subcutaneous injection, timed to the post-workout window — the mechanical-damage signal it is proposed to amplify. No human trial has set a dose or confirmed efficacy; the ranges below are community convention built on the (contested) overload theory. Read this as a map of how the compound is actually used, not a validated prescription.

Community convention on a contested mechanism: the synthetic peptide's unique activity was not replicated in an independent study, no human trial exists, and it is WADA-prohibited. Every number here is a usage pattern, not evidence.

Tiered dose ranges

The defining variable is training intensity — MGF's premise is that it amplifies a mechanical-overload signal, so dose follows the stimulus.

Low / introductory:: 100–200 mcg per session — first use or lighter training days; establishes tolerance with minimum systemic load.
Standard:: 200–300 mcg per session — the most common range in community protocols, used after moderate-to-hard resistance training.
High / heavy training:: 300–400 mcg per session — reserved for the heaviest training blocks (high-volume eccentric or damaging work); not used daily.

Subcutaneous administration

MGF is injected subcutaneously into or near the muscle just trained — the site-specific logic follows directly from the proposed local repair mechanism.

Injection site:: Subcutaneous tissue overlying the target muscle (e.g. lateral quad after leg training, lateral deltoid after shoulder training). Inject within 30–60 minutes post-workout to land inside the mechanical-damage window. Rotate between adjacent sites within the same region each session to prevent local irritation.
Measuring the dose:: Drawn on a U-100 (100-unit / 1 mL) insulin syringe from the reconstituted vial. At the standard 2 mg / 2 mL mix (1,000 mcg per mL): 100 mcg = 10 IU · 200 mcg = 20 IU · 300 mcg = 30 IU · 400 mcg = 40 IU. The on-page calculator adjusts for any vial size.
Timing:: Post-workout is the consensus — specifically tied to when mechanical damage has already occurred; see Best time to dose above. Pre-workout use has no supporting logic in the overload framework. Because MGF is reported as very short-lived (degraded rapidly without PEGylation), the window is kept tight.
Food window:: Subcutaneous injection is not dependent on gastric emptying; food timing is a non-issue for the injection itself. If stacking with an IGF variant on the same day, plan the post-workout meal to manage glucose.

Cycle & washout

MGF is almost always used in short, training-tied blocks rather than continuous daily dosing.

Frequency per week:: 2–4 times per week on training days only — matched to sessions involving the target muscle group. Using it on rest days has no mechanistic basis in the overload model.
Cycle duration:: 4–6 weeks per block, then pause. Most community protocols run MGF for the peak of a strength or hypertrophy training cycle.
Washout:: 2–4 weeks off between blocks. Because no human PK data exist, washout length is conservative convention — erring on the side of allowing any axis adaptation to reset.
IGF-axis caution:: If stacking with IGF-1 LR3 or IGF-1 DES on the same days, monitor for blood-sugar dips — the combined IGF-pathway load can cause hypoglycemia, especially fasted.

Reconstitution at a glance

The on-page calculator handles any vial size; the quick reference for a 2 mg vial (the standard Ki Peptides size):

Mixing:: 2 mg vial + 2 mL bacteriostatic water = 1,000 mcg per mL. On a 100-unit (1 mL) insulin syringe: 100 mcg = 10 IU · 200 mcg = 20 IU · 300 mcg = 30 IU · 400 mcg = 40 IU.
Why 2 mL:: Keeps the per-IU increment at 10 mcg, so typical 100–400 mcg doses fall on clean 10–40 IU marks with no rounding error.

Sources:PMID 16244184 PMID 20130113 PMID 24253050

Substrate the signal needs

Nutritional cofactor precision

MGF's proposed role is amplifying the repair signal that mechanical overload generates in muscle. Its cofactors map onto three questions: what gives the signal something to act on (the stimulus), what does the repair process consume (the substrate), and what cost does the IGF-axis load create (the mitigation).

Reasoned from MGF's proposed overload-response mechanism plus muscle-repair physiology — not an MGF cofactor study. The mechanism itself is contested. Supplement doses are community/practitioner ranges, not MGF-specific findings.

The training stimulus (the primary cofactor)

Resistance training — especially eccentric, muscle-damaging work — is what gives MGF its signal to amplify. Without a mechanical-overload event in the injected muscle, there is no upstream signal and no rationale for the injection.

Why it is a cofactor:: MGF in the natural model is produced locally in response to muscle damage. The synthetic peptide is administered on the premise that it mimics or extends that local response. A light cardio session generates minimal mechanical damage and therefore provides little for MGF to act on — heavy compound lifts, eccentric-focused sets, or volume blocks are the stimulus that makes the protocol coherent.
Protocol integration:: Inject into the worked muscle on days that include high-effort resistance training for that muscle group (e.g. quad sweep or rectus after a leg day with heavy squats + Romanian deadlifts). Prioritize sessions with substantial eccentric loading — the phase most associated with muscle-fiber microtrauma and subsequent satellite-cell activation.

Protein + leucine (supply the repair substrate)

A repair-activation signal accomplishes nothing without the amino acids to build with. Protein and the key trigger amino acid leucine are the substrate the signal is meant to deploy.

Protein target:: 1.8–2.2 g per kilogram of body weight per day (≈ 0.8–1.0 g per pound) — toward the higher end during active training blocks where MGF is in use. Total daily intake is what matters; evenly distributed across 3–5 meals limits per-meal waste.
Leucine timing:: A post-workout dose of 2.5–3 g leucine (or a meal rich in leucine — roughly 40–50 g of whey or animal protein) within 30–60 minutes of training. Leucine is the amino acid that trips the mTOR switch for protein synthesis; it is the match that lights what a repair signal sets up.
Why the window matters:: MGF is injected post-workout; the post-workout meal lands in the same window. Amino acid availability at the moment a muscle-repair signal fires is not incidental — synthesis requires substrate.

Glucose management (mitigate the IGF-axis cost)

MGF is often stacked with IGF-1 DES or IGF-1 LR3 on the same training days. Both IGF variants lower blood sugar. Managing glucose is the one meaningful cost to offset.

The risk:: Any IGF-axis compound — including IGF-1 DES and LR3 that commonly pair with MGF — can cause hypoglycemia, particularly when injected fasted or in a large caloric deficit. The risk compounds when two IGF-pathway agents are used the same day.
Protocol integration:: Do not inject on an empty stomach if stacking with an IGF variant. A carbohydrate-containing post-workout meal (40–60 g fast carbs: rice, fruit, sports drink) in the same window dampens the glucose dip. Keep simple sugars on hand during the injection window.
When MGF is used alone:: The glucose-management concern is minimal — MGF's own IGF-signaling effect (if real) is local and brief. The protocol above applies primarily when IGF-1 DES or LR3 is co-administered.

Combinations + timing

Stacking notes + timing windows

MGF's proposed role is a brief, local satellite-cell activation signal immediately post-damage. Its most coherent pairings extend that signal into a different biological phase — from activation into proliferation — or substitute a longer-acting form. Pairing MGF with another mechano-growth signal (another peptide that recruits the same satellite-cell pathway) is mechanistically redundant.

User combinations reasoned from complementary mechanisms — doubly speculative because the MGF mechanism itself is contested. Doses below are community convention; "reach for" describes where users go, not a proven indication. All stacks are WADA-prohibited territory.

MGF + IGF-1 DES

The most targeted local-growth sequence: MGF proposed to activate satellite cells in the damaged site, IGF-1 DES proposed to drive their proliferation.

Why it works:: IGF-1 DES (the des-1-3 truncated variant) binds the IGF-1 receptor with higher affinity than standard IGF-1 but has a very short half-life — it is also treated as a local, site-injected compound. In the community model: MGF fires first (the alarm) and IGF-1 DES follows (the growth signal that acts on the now-active satellite cells). Two different roles — activation, then proliferation — rather than two activation signals.
The protocol:: MGF 200–300 mcg subcutaneous post-workout into the target muscle, followed 15–30 minutes later by IGF-1 DES 50–100 mcg subcutaneous at the same or adjacent site. Both are site-injected on training days only; sequencing MGF first then DES mimics the proposed natural order.
Outcome:: Reached for by users targeting hypertrophy or site-specific recomposition in the trained muscle during a high-volume training block. Glucose management is essential — two IGF-pathway compounds on the same day amplify hypoglycemia risk.

MGF + IGF-1 LR3

A broader pairing: local activation signal (MGF) layered on top of a long-acting systemic growth signal (IGF-1 LR3).

Why it works:: IGF-1 LR3 is a long-acting IGF-1 analogue that operates systemically over hours, driving generalized anabolism and proliferation across muscle tissue. MGF in this model provides a local, post-damage activation pulse at the specific site — the idea being that LR3 provides the growth environment and MGF targets it to the just-trained muscle. Different half-lives and proposed scopes of action.
The protocol:: MGF 200–400 mcg subcutaneous post-workout into the target muscle; IGF-1 LR3 40–80 mcg subcutaneous (commonly abdomen or quad, not necessarily site-specific) also post-workout or within 1–2 hours. LR3 is typically run daily or 5-on-2-off for the cycle; MGF on training days only for that muscle.
Outcome:: The combination users reach for during peak hypertrophy or strength cycles where whole-body anabolism and localized repair are both goals. Requires careful glucose monitoring — LR3's long window combined with MGF's acute IGF-axis load creates a sustained hypoglycemia window.

MGF vs. PEG-MGF — not a stack

PEG-MGF is the longer-acting sibling, not a complement. Using both together is redundant — they address the same proposed signal with different half-lives.

The difference:: PEG-MGF attaches a polyethylene-glycol chain to slow MGF's rapid degradation, extending its circulating half-life and making it more systemic. Plain MGF is treated as a short, local, post-workout pulse; PEG-MGF is the slower, sustained version of the same proposed signal.
Why not to stack them:: They work through the same proposed mechanism — piling them together doubles the mechanistic lever rather than adding a complementary one. Choose one: plain MGF for a brief, site-targeted pulse timed to training; PEG-MGF for a longer-acting, less time-dependent version. See the PEG-MGF page for its dosing and timing specifics.
When plain MGF wins:: Post-workout, site-specific, training-day-only protocols — the short half-life is a feature when the goal is a timed local pulse rather than sustained systemic exposure.

Reconstitution math

Reconstitution calculator

Calculated for a 1 mL U-100 insulin syringe (100 units/mL).

Peptide per vial

BAC water added

Desired dose

Units per dose

Draw to this mark on a U-100 syringe

Volume per dose: 0.2 mL
Doses per vial: 10
Concentration: 1 mg/mL

One vial lasts

Daily: 10 days
Every other day: 20 days
5×/week: 14 days

Research use only. Not for human consumption. Outputs are reference values based on research literature — verify all measurements independently.

From the studies

Side effects from research

There is no human safety data for MGF — the points below come from what is known about the IGF-1 axis generally and from the nature of the compound.

Because the headline mechanism is contested, even the intended effects are uncertain; commonly reported user effects (injection-site reactions, etc.) are anecdotal. The theoretical concern that applies to the whole IGF-1 axis applies here too — any agent that genuinely promotes cell proliferation raises a theoretical cancer-promotion concern — and has not been studied for MGF in humans. No human organ-overgrowth or long-term data exist.

Sources:PMID 20130113 PMID 24253050

As reported in literature

Research dosing ranges

These are doses and findings from the published research — all animal or cell-culture, since no human data exist. They are shown separately so research figures are never mistaken for a human dose. Read them alongside the contradiction: the proliferation/satellite-cell findings come largely from the originating group, while an independent replication found no unique activity for the synthetic peptide. No reliable human half-life has been published.

Dose	Route	Model	Outcome	Sources:
In vitro	Cell-culture media	Human myoblasts (Goldspink group)	Reported to increase proliferation and block differentiation (satellite-cell activation theory)	PMID 16244184
In vitro	Cell-culture media	Myoblasts (independent replication)	Synthetic E-domain peptide showed NO unique biological activity	PMID 24253050
Local injection	Intramuscular	Rat muscle (overload/damage models)	Reported faster early repair vs IGF-1 in originating-group studies	PMID 20130113

Quick answers

Frequently asked

What is MGF?

MGF (Mechano-Growth Factor) is a peptide based on a splice variant of the IGF-1 gene (IGF-1Ec) that muscle produces after mechanical overload. The research peptide is the short, unique tail of that variant — the 24-amino-acid "E-domain." It is sold as a research reagent, not a medicine.

Does MGF actually work the way it's claimed?

It is genuinely contested. The originating group proposed MGF is a distinct local repair signal that activates muscle stem cells through its own receptor. But an independent study found the synthetic peptide had no unique activity, no free natural version of the peptide has ever been isolated from tissue, and its proposed receptor has never been identified. Treat the mechanism as an unproven hypothesis.

What is the difference between MGF and PEG-MGF?

Same core peptide, different lifespan. Plain MGF is reported to break down very quickly, so it is treated as a brief, local, post-workout pulse. PEG-MGF attaches a polyethylene-glycol (PEG) chain to slow that breakdown, aiming for a longer-acting, more systemic version. Note that essentially all of the underlying biology studies used unmodified MGF, not the PEGylated form.

Is MGF an approved drug?

No. It has no approved human therapeutic use and has never been tested in humans as a therapy. It is a research reagent, and it is prohibited in sport by WADA (Section S2.3, which explicitly names mechano growth factors). This page presents research literature only and makes no medical claims.

How is MGF commonly dosed?

No human trial has set a dose. In the user community the common pattern is 200–400 mcg per session by subcutaneous injection into the worked muscle, post-workout, a few times per week on training days. Treat that as convention built on a contested theory, not a recommendation.

Primary sources

References

PMID 16244184Goldspink 2005 (MGF / mechano-growth-factor hypothesis)
PMID 24253050Fornaro et al. 2014 (no unique activity for synthetic E-peptide)
PMID 20130113Matheny et al. 2010 (MGF / IGF-1 E-domain review)
PubChem CID 175675731PubChem CID 175675731 (MGF 24-AA peptide)
WADA S2WADA Prohibited List S2

Research use only · Not medical advice · Updated 2026-06-01