MGF was discovered by Goldspink and was named MGF because it is exclusively regulated by mechanical loading. It is splice variant of the IGF-1. Means IGf-1 is spliced to become MGF. It kick starts the satellite cell differentiation and also help in proliferation in the muscle.So it is the key player in muscle growth.
The problem is that we don’t know much about how to manipulate MGF with loading. there was a study which showed greater MGf release with eccentrics but their control group was a bit shady.