some say growth hormone makes new muscle cells and some say it makes the existing muscle cells bigger.?
Yes growth hormone can help to cause muscle cell proliferation..{ Hyperplasia}. Where as Anabolic Steroids cause the existing muscle to fill with stores and become bigger. {Hypertrophy}
I have not been able to find scientific proof anywhere supporting that GH makes new additional muscle cells but Im still looking. What is your opinion and do you have supporting evidence?
Growth hormone apparently causes an increase in IGF-1 which can help to cause muscle cell Hyperplasia in conjunction with MGF {which is also a type of IGF}
Here's an article about IGF and MGF and how they work together to cause muscle cell proliferation.
The science:
In a natural system (Our Body) we have peaks and dips with MGF and IGF levels. The reasons for these peaks and dips are to create the ideal amount of cells to repair and create new tissue. After strenuous exercise the levels of MGF in the body (more specifically in the muscle just trained) increase dramatically and there is a dramatic decrease of IGF levels. The reason for this is because MGF causes stem cells to proliferate (split and multiply). This process ensures that there are enough cells available to make repairs and to create new tissue in order for the tissue to function efficiently and properly (in this case skeletal muscle tissue). As mentioned above in the presence of MGF there is no need for IGF because it is rendered useless and cannot activate the stem cells, so this explains the bodies response to decrease IGF levels.
In 12-36 hours MGF levels begin to drop and there is a direct correlation in the rise of IGF levels within the body. Stem cells have proliferated and now the IGF will bind to the proper receptors and cause differentiation (force the stem cells to form into a specific cell for a specific tissue type). This process repeats every time you exercise and keeps the natural system in an efficient state.
When flooding the body with these artificial peptides a person will change this natural system dramatically. A person using MGF only is causing stem cell proliferation while at the same time preventing IGF to perform its duties of creating new tissue from those newly created stem cells. A person using IGF only is depleting the supply of stem cells at a rate much faster than the body can keep up, leading to a depletion of available stem cells and not receptor "down-regulation" or "desensitization."
http://www.getbig.com/boards/index.php?topic=210966.0;wap2