Human Growth Hormone (HGH or GH) is necessary for proper physical development in childhood and puberty.
Its functions in adulthood are important but less understood.
It seems that GH must be present in the body in proper levels: too little of growth hormone is probably just as bad as too much of it.
GH is normally secreted in pulses during sleep and probably after exercise. There is a general consensus among some researchers that a certain threshold exists: the exercise must be of some intensity and possibly of some minimum duration (R.J. Godfrey places this threshold at 10 minutes of intensive exercise).
Other scientists claim that GH is released regardless of any threshold, with aerobic and anaerobic exercise. L. Wideman and colleagues claim that the GH release is greater in young women than in young men and that GH release is significantly lower in older individuals. (http://www.ncbi.nlm.nih.gov/pubmed/12457419 ) This would mean that GH may not play very important role in muscle growth as resistance exercise leads to much smaller muscle gains in women than in men and aerobic exercise does not cause almost any muscle hypertrophy.
Effects of high GH levels
Growth/thickening of jaw bone, fingers, toes
Thickening of connective tissue
Growth/enlargement of internal organs
Insulin resistance, diabetes type II
Cardiovascular problems due to myocardial hypertrophy (enlargement of heart)
Effects of low GH levels
Increase in SHBG (Sex-Hormone Binding Globulin) resulting in lower levels of free testosterone
Muscle mass loss
Truncal (around the waist) obesity
GH as doping
Growth Hormone therapy has very good results in people with GH deficiencies: in such cases (especially in children and teenagers), GH indeed promotes development, muscle growth, normal testosterone levels.
This, together with the fact that GH is associated with various growth factors (especially the IGF family) that are thought to promote muscle growth, led some coaches and athletes to believe that supraphysiological doses of GH can help in performance enhancement and muscle growth.
As for performance enhancement, be it strength or endurance, there are no signs that GH can be of any help. On the contrary: M.J. Rennie describes in his article “Claims for the anabolic effects of growth hormone: a case of the Emperor’s new clothes?” research by Dr. Kai Lange of Danish Institute of Sports Medicine. The trials with healthy athletes showed significant loss of endurance after external GH supplementation.
Rennie explains that: “There is good evidence that hGH administration exacerbates the pronounced increase in lipolysis that occurs during exercise and, in addition, increases the production of lactate and protons by working muscles. The inevitable metabolic acidaemia and consequent reduction in the rate of glycogenolysis in muscle and liver could explain the acutely decreased performance. Furthermore, because of the effect of rhGH in decreasing glycogen storage in muscle and liver, it will make recovery from exercise more difﬁcult. However, a bigger danger is probably the unphysiologically high fatty acidaemia, which could promote cardiac arrhythmia.”
H. Liu and colleagues reviewed 44 articles describing 27 various study samples published between 1966 and 2007.
Their meta-study showed that GH can increase lean body mass, it may not improve strength and it may worsen exercise capacity.
Muscle growth with GH: an open question
In adulthood, GH apparently doesn’t cause muscle growth. Unnaturally low GH levels can, however, lead to loss of muscle tissue.
Externally administered GH can facilitate connective-tissue growth. It is also possible that GH can increase the synthesis of connective tissue within muscle and thus lead to increases in total muscle size. Such increases are, however, thought to be short-lived.
According to most studies, supraphysiological doses of GH do not cause protein synthesis in the muscle of healthy individuals (http://www.ncbi.nlm.nih.gov/pmc/articles/PMC2657499/?tool=pmcentrez ).
E. T. Schroeder and colleagues compared 3 groups of elderly men (average age 71 years): first group received testosterone supplementation, second group was using testosterone and GH and the third group was a control group taking placebo.
Although there were no differences in performance after 8 weeks of administration, the lean body mass increased by average of 1.5 kg for the testosterone group and 2.14 kg for testosterone + GH group.
The exact nature of this increase is not clear. It may be caused by increases in connective tissue or it may point to protein synthesis and muscle fiber growth.
M.G. Giannoulis and colleagues came to similar conclusion in another clinical trial with older men. (http://www.ncbi.nlm.nih.gov/pubmed/16332938 )
Amino acids and Growth Hormone
Some amino acids, namely arginine, lysine and ornithine are known to increase the GH levels when used intravenously (IV). Oral use of these amino acids has not been found to increase GH levels and muscle mass. (http://www.ncbi.nlm.nih.gov/pubmed/12093449 , http://www.ncbi.nlm.nih.gov/pubmed/8220395 ).
This is not to say that amino acids have no place in bodybuilding supplementation but their impact on GH levels seems to be negligible.