MGF (mechano growth factor) has been used by bodybuilders and athletes for a few years already. After resistance exercise, IGF-1 is released within the muscle. Specifically, at this time, immediately following the mechanical use of a muscle, the IGF-I gene is spliced towards MGF which initiates hypertrophy and repair of local muscle damage. It does so both by activating muscle stem cells and satellite cells, but also via various other anabolic processes. It differs from "regular" IGF-1 mainly due to it's C-Terminal sequence.
In a rodent study, a single intramuscular injection into muscle resulted in a 25% increase in mean muscle fibre cross section area within three weeks. Using a similar protocol, liver-derived IGF-1 took four months to produce a 15% increase.
It would also appear that with regards to age, the young have a better ability to respond to MGF, and that the elderly experience a decreased response to MGF which results in a decreased ability to stimulate the growth of new muscle tissue.