Human Growth Hormone is made in the body by the pituitary gland. Before this happens, Growth Hormone Releasing Hormone and Somatostatin are released by the hypothalamus, and that regulates whether more or less HGH is produced by the pituitary. Many factors influence the release of HGH, including nutrition and exercise.
Once released, HGH has many functions in the human body. HGH is a protein that stimulates the body cells to increase both in size, as well as get more rapid cell division than usual. Additionally, it enhances the movement of amino acids through cell membranes and also increases the rate at which these cells convert these molecules into proteins. Understandably, you can see that this would amount to a muscle building effect in the human body. HGH also has the ability to cause cells to lessen the normal rate at which they utilize carbs, and simultaneously increase the rate at which they use fats.
Fat loss and lean mass increases with HGH have been found at a low dose, however, that would be inadequate amounts to gain muscle. Using 3-6iu for a 220lbs bodybuilder is the range most bodybuilders and athletes are finding their best results with. A length of time in the 24 week range is very typical of HGH, and individuals usually experience consistent results starting well after the 2-month-mark, and they tend to either run this stuff for around 6 months at a time, or year-round if it can be afforded
Athletes at rest were observed in one study to be in an anabolic state . So you can essentially run marathons and take this stuff, and still build some muscle. Pretty amazing!
HGH is usually secreted in rhythmic pulses while you are sleeping, as two peptides, Human Growth Hormone RH and Somatostatin and are alternately released. Human Growth Hormone RH (Growth Hormone Releasing Hormone) is the one responsible for the Release of Growth Hormone
HGH also has the ability to stimulate the production or reproduction, in the case of an injury, of cartilage. However this requires the presence of a mediator substance IGF, which is released from the liver in response to Human Growth Hormone, and the IGF, in turn, actually promotes the growth of cartilage.
Although HGH requires IGF to actually grow new cartilage, HGH is directly able to stimulate the elongation of bone tissue, and HGH has also been shown to elicit a positive effects on making more red blood cells, which is great for both anabolism as well as endurance. (due to more nutrition and oxygen to the body)
The majority of your HGH natural production is during your early years, when you are experiencing growth spurts. As you get older, you just make less of this it, and its effects are much less noticeable. Although Human Growth Hormone can easily make very nice, quality weight and muscle increases, its a not great for strength gains by itself.
Personally I would recommend staying in the 3-6 iu mark for a duration rather than 6-10iu for a shorter period when getting a set amount.