Mechano Growth Factor (MGF) is a variant of the Insulin-like Growth Factor 1 (IGF-1) hormone. It is released in response to muscle stretching and micro trauma from exercise under the regulation of Growth Hormone (GH). Once released under these circumstances it gets to work by activating the muscle satellite cells and kick starting the hypertrophy cascade which leads to bigger and stronger muscles. Fairly recently researchers in the UK have been looking at the potential of GH for this purpose. They gave the elderly men GH and had them train their legs. The results showed a marked increase in muscle mass. Of course the researchers are looking into this for potential therapies to overcome muscle wasting diseases, but obviously bodybuilders will see this as a means of getting bigger. Professional athletes willing to cheat will see this as a way of getting an edge, which is currently undetectable. And its accessibility seems to be quite high, with several vendors showing up from a simple internet search. Time will eventually tell whether this catches on.
Source: Evans RM, Harridge SD, Velloso CP, Yang SY, Goldspink G, Orrell RW. Investigation of MGF mRNA expression in patients with amyotrophic lateral sclerosis using parallel in vivo and in vitro approaches. Amyotroph Lateral Scler. 2009 Jul 1:1-6.