GH does cause hyperplasia. (the growth of new cells). it does not only affect muscle. it can cause growth in all cell types including, muscle, organ tissue, cancerous cells, etc. One of the bodybuilding benefits of hyperplasia is that because of the new muscle cells, mass can be increased much farther than with traditional anabolic agents causing hypertrophy (enlargement of cells). so gh allows you to grow new cells that you can make bigger through training and AAS.