GDF-8 - 85%
Myostatin (also known as growth differentiation factor 8, abbreviated GDF-8) is a myokine, a protein produced and released by myocytes that act on muscle cells' autocrine function to inhibit myogenesis: muscle cell growth and differentiation.
In humans, it is encoded by the MSTN gene. 
Myostatin is a secreted growth differentiation factor that is a member of the TGF beta protein family.