MGF, mechano growth factor, is not a separate peptide given from outside but a variant of IGF-1 that muscle produces itself after loading and microdamage. Its distinguishing fragment is 24 amino acids long and, on the hypothesis, is meant to prompt satellite cells to repair the fibre. Synthetic MGF breaks down within minutes, so polyethylene glycol is attached to it and PEG-MGF is produced, acting over hours or days. This whole construction rests on studies in rodents and in cell culture. There are no randomised studies in humans, and one independent team did not confirm the basic effect. Both peptides are research substances and both are banned in sport.
What is MGF?
MGF is one of the forms in which the IGF-1 gene is read. The body splices that gene in different ways. The IGF-1Ea form is the systemic version, produced mainly in the liver. The IGF-1Ec form is the local version, responding to mechanical stimulus, and it is that one which is called mechano growth factor. It contains a core shared with IGF-1 plus a specific insert, from which, after cleavage, the final E fragment of about 24 amino acids is produced. That fragment is credited with a role distinct from the mature part of IGF-1. Expression of MGF is transient and peaks earlier than the systemic form. The context of the whole IGF-1 axis in muscle is in the article on muscle peptides, and other altered forms of IGF-1 in the article on IGF-1 LR3 and DES(1-3) IGF-1.
What is MGF supposed to do in muscle?
The hypothesis from the Goldspink group holds that the E fragment activates satellite cells. These are dormant muscle stem cells that wake when a fibre is damaged. MGF is meant to push them to divide and to delay their differentiation, which widens the window for repair. In cell culture and in animals the E fragment did indeed increase proliferation and hold back differentiation, behaving like a local repair factor responding to load. That is the theory that made this peptide famous among athletes.
The promise ran: local muscle growth after injection into a particular area, without raising IGF-1 throughout the body. The problem is that the step from a cell in a dish to a human muscle after an injection of the peptide has never been studied in a controlled way. The observation that muscle produces MGF after training says nothing about what a dose of MGF from a vial will do.
Why was PEG-MGF created?
The reason is the instability of the natural E fragment. Its half-life is counted in minutes, because protein-cutting enzymes break it down quickly. Pegylation means attaching a chain of polyethylene glycol to the peptide. That shield slows the breakdown, so PEG-MGF persists under research conditions for hours or even days. There is a cost: PEG-MGF is a molecule that does not occur naturally in the body, so its behaviour does not match the short, natural MGF impulse.
What did the research confirm, and what did it not?
- It was shown that the body’s own MGF rises in muscle after exercise and after fibre damage.
- It was shown that in cell culture and in rodents the E fragment increases satellite cell proliferation and holds back their differentiation.
- There are no completed randomised studies of giving MGF or PEG-MGF to humans. Only observations of the body’s own expression after exercise exist.
- An independent laboratory found no stimulatory effect of MGF on human myoblasts, which undercuts one of the original findings of the Goldspink group.
In other words, the mechanism is described at the level of the cell, while its translation to a human after injection remains untested.
What is the legal and sporting status of MGF?
Neither MGF nor PEG-MGF is approved as a medicine in the United States, the European Union or anywhere else. They are sold as MGF and PEG-MGF, as reagents for research. On the WADA prohibited list they appear in group S2, covering peptide hormones and growth factors, with a ban that applies all year. More on the legal categories is in the article on the legal status of peptides and on the legal warning page.
Frequently asked questions
What is the difference between MGF and PEG-MGF?
It is the same E fragment sequence. PEG-MGF has a polyethylene glycol chain attached, which extends the action from minutes to hours or days. Natural MGF works as a short impulse.
Is MGF a peptide independent of IGF-1?
No. MGF is one of the forms of the IGF-1 gene, designated IGF-1Ec, produced after muscle loading. Its E fragment is hypothesised to act independently of the mature part of IGF-1.
Does MGF build muscle in humans?
It is not known. There are no randomised studies of giving it to humans, and one independent laboratory did not confirm the basic effect on human muscle cells.
Can MGF be used in sport?
No. MGF and PEG-MGF are on the WADA prohibited list in group S2 and are banned all year, in and out of competition.
Where this information comes from
The splicing of the IGF-1 gene into the IGF-1Ea and IGF-1Ec forms, the 24 amino acid E fragment and the transient expression peaking earlier than the systemic form come from the published work on mechano growth factor. The satellite cell hypothesis and the results in cell culture and rodents come from the Goldspink group’s papers; the failure to reproduce the stimulatory effect on human myoblasts comes from an independent laboratory’s report. The minute-scale half-life of the natural fragment and the effect of pegylation come from the same literature. The group S2 listing comes from the WADA prohibited list. These sources were checked on 6 September 2026.