A few years ago I was on hGH SC injections and had very good IGF-1 response relative to hGH dose.
Back on hCG again and with IM injections, IGF-1 levels were relatively low.
Did 3 months SC and IGF-1 levels are now very robust.
SC and IM are known to release the same GH under the curve and SC produces slower release to blood stream. GH is transported in venous blood flow in both cases to the liver via the heart and arteries where GH causes IGF-1 release by the liver.
It seems that the fast release of GH from hGH IM injections may present more GH to the liver than the liver can utilize as IGF-1 release in the liver may be rate limited and "time under the GH curve" then seems more important than "area under the GH curve" and IGF-1 release is then somewhat not linear to serum GH levels.
There is also a lesson for the body builders who use large amounts of hGH; they may be better off with more than one smaller SC injection per day to maximize time under the GH curve.