PEG MGF refers to pegylated mechano growth factor. This is a spliced variant of the I-G-F gene that is used by animals to increase their stem cell count within the muscle tissue while encouraging muscle fibers to mature and fuse.

This system is largely used to produce adult muscle as rats mature. The natural version of this peptide is developed where needed and does not travel through the bloodstream; synthetic versions of this chemical have been altered so they may remain stable in the bloodstream for a few minutes.

Pegylation refers to the chemical's ability to attract polyethylene glycol from larger molecules. In this case, the peptide is specifically designed to fuel the breakdown of MGF. PEG molecules can act as a protective coating for the portion of MGF they attract. In theory this would allow MGF to be carried through the bloodstream without being broken down so it can reach its destination more successfully.