HGH and IGF-1, which is a result of its use is the only substance that can actually cause hyperplasia / Worn muscle cells / While use of anabolic steroids can cause hypertrophy only (enlargement of existing muscle cells). HGH also increases protein synthesis, which may be responsible for hypertrophy. You must also understand that normally, after puberty, the body stops influence the growth of new muscle cells. Number of muscle cells is genetically determined for the rest of my life, moreover, what we can do for your muscles, the larger size of these cells through weight training or using steroids. However, using HGH the body can actually start grow new muscle cells.