Well, there have been studies that show a spike in HGH when a certain level of physical exertion is preformed, such as high intensity exercises that also includes things like sprints and the like -- not just weight training. Also, about ten years ago I had to take some kind of insulin test or something where they injected insulin into my veins and then when I was about to pass out (I actually did pass out) they would then inject dextrose into another vein. One of the things that was shown was there was a definite spike in HGH levels when my blood sugar was low. So, assuming I had a good nights sleep, which I did, and produced normal levels of GH (no reason to assume I didn't), then this would prove that a production of HGH eight hours before my test had no "suppressive" effect on my own HGH production. And if a GH surge (such as during sleep) would produce a suppressive effect for 24 hours then it would not be possible to have any other kind of GH spike during the day or during high intensity exercise. Remember, just like testosterone, your body doesn't know where the hormone is coming from. Whether it's from your pituitary or from an insulin pin it's all the same as far as your body is concerned. This was explained to me by my endocrinologist in regard to testosterone and he said that it also applied to HGH.