Introduction[edit | edit source]
Human growth hormone (HGH), also known as somatotropin, is a 191 amino acid single-chain polypeptide. It is produced by somatotropic cells within the anterior pituitary gland.
HGH has numerous roles throughout life, from growth itself (including the turnover of muscle, bone and collagen) to the regulation of particular aspects of metabolic function, for example increased fat metabolism and the maintenance of a healthier body composition in later life.
HGH is secreted in a pulsatory way, roughly following a circadian rhythm. Various physiological stimuli can cause HGH secretion, with the most influential non-pharmacological stimuli being sleep and exercise.
Once secreted, HGH remains active in the bloodstream for a few minutes, allowing enough time for the liver to convert it into growth factors, the most crucial being insulin-like growth factor (IGF-1), which has growth-promoting effects on every cell in the body. Together, IGF-1 and GH promote normal growth of bones and tissues.
Synthetic human growth hormone has become a target of abuse in the sporting world with its benefits in a healthy, adults uncertain.The use or distribution of HGH without a medical need and prescription is considered illegal.
HGH Roles in Childhood and Adulthood[edit | edit source]
HGH acts on many parts of the body to promote growth in children. When the growth plates in the bones (epiphyses) have fused, HGH no longer increases height, but it still has important roles. In adulthood HGH impacts the bodies metabolism (how your body turns the food you eat into energy).
- Growth: HGH induces growth in nearly every tissue and organ in the body. However, it is best known for its growth-promoting effect on cartilage and bone, especially in the adolescent years.
- Metabolic Effects: HGH impacts metabolism primarily by up-regulating the production of insulin-like growth factor-1 and its subsequent effect on peripheral cells. Predominantly, cells move into an anabolic protein state with increased amino acid uptake, protein synthesis, and decreased catabolism of proteins. Most particularly it is known for its effect on bone growth and musculoskeletal anabolism
- Regulation of lipid metabolism, body fat distribution, inflammation and vascular health . HGH secretion is effected by visceral fat. The adverse metabolic effects of increased visceral fat (eg metabolic syndrome) include HGH deficiency, with therapy to increase HGH significantly reduces visceral fat. Visceral fat accumulation is strongly associated with increased metabolic and cardiovascular risk, whereas subcutaneous fat appears to be beneficial with respect to metabolic health A 2015 review reinforces this, indicating that growth hormone-releasing hormone (GHRH) may be beneficial for people with obesity.
- Another role of HGH is blood sugar level control. HGH indirectly acts on blood glucose levels through the regulation of IGF-1, which mimics insulin's effect in the body, helping control blood sugar levels.
Physiotherapy Implications[edit | edit source]
The release of HGH is sensitive to many pharmacologic and physiologic stimuli, including exercise.
Exercise is a forceful physiological stimulus for HGH secretion, with both aerobic and resistance exercise bringing about a significant, acute increases in HGH secretion. In opposition to previous suggestions that exercise-induced HGH release requires that a "threshold" intensity be attained, recent research shows that regardless of age or gender, there is a linear relationship between the magnitude of the acute increase in HGH release and exercise intensity.
For both endurance and resistance exercise, greater activation of anaerobic glycolysis and lactate formation increases the amount of HGH released. For example : Research shows that regular resistance exercise, such as the use of dumbbells and bodybuilding machines, lead to increased secretion of HGH and insulin-like growth factor-1.
- GH secretion decreases with ageing and obesity.
- Exercise is a robust stimulus of GH secretion, as as such is a great natural way to promote eg better bone, joint and muscle health.
Altered HGH Levels[edit | edit source]
HGH is very important for regulating growth.
- Higher than normal levels of HGH result in gigantism or acromegaly.
- HGH deficiency results in a growth deficit in children and the GH deficiency syndrome in adults. eg. hypopituitarism due to a benign pituitary adenoma or damage to the pituitary gland or hypothalamus.
References[edit | edit source]
- Brinkman JE, Tariq MA, Leavitt L, Sharma S. Physiology, Growth Hormone. InStatPearls [Internet] 2020 May 16. StatPearls Publishing. Available:https://www.ncbi.nlm.nih.gov/books/NBK482141/ (accessed 16.8.2022)
- Medline plus IGF 1 Test Available:https://medlineplus.gov/lab-tests/igf-1-insulin-like-growth-factor-1-test/ (accessed 16.8.2022)
- Siebert DM, Rao AL. The use and abuse of human growth hormone in sports. Sports Health. 2018 Sep;10(5):419-26. Available:https://pubmed.ncbi.nlm.nih.gov/29932857/ (accessed 17.8.20220
- Dr Axe 9 Benefits of Human Growth Hormone, Including More Muscle & Less Fat Available:https://draxe.com/nutrition/human-growth-hormone/ (accessed 17.8.2022)
- Stanley TL, Grinspoon SK. Effects of growth hormone–releasing hormone on visceral fat, metabolic, and cardiovascular indices in human studies. Growth Hormone & IGF Research. 2015 Apr 1;25(2):59-65. Available: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4324360/(accessed 16.8.2022)
- Gilmore Health Role of HGH on Glucose Homeostasis in Humans Available:https://www.gilmorehealth.com/role-of-hgh-on-glucose-homeostasis-in-humans/ (accessed 16.8.2022)
- Godfrey RJ, Madgwick Z, Whyte GP. The exercise-induced growth hormone response in athletes. Sports medicine. 2003 Jul;33(8):599-613. Available:https://pubmed.ncbi.nlm.nih.gov/12797841/ (accessed 16.8.2022)
- Roemmich JN, Rogol AD. Exercise and growth hormone: does one affect the other?. The Journal of pediatrics. 1997 Jul 1;131(1):S75-80. Available:https://www.sciencedirect.com/science/article/abs/pii/S0022347697700179 (accessed 18.8.2022)
- Cleveland Clinics HGH Available:https://my.clevelandclinic.org/health/articles/23309-human-growth-hormone-hgh (accessed 17.8.2022)