Growth Hormone Response to Exercise
Growth hormone is a polypeptide that is produced by the anterior part of our pituitary gland situated at the base of our brain. It represents a family of proteins and not just simply composed of a single hormone, which makes it irreplaceable by synthetic forms.
Since GH is not fully understood, we can only define it based on the benefits it provides. Of the greater benefits of GH are protein conservation, stimulation of lipolysis, and fat oxidation. Elevated GH levels influences nitrogen retention in our muscles with an increase in protein synthesis. Its anabolic or muscle building effects is observed through an increased transcription of DNA leading to increased quantities of RNA. It has also been shown to alter body composition, increased protein metabolism and decreased protein catabolism, and a decrease in stored and circulating lipids. This lipid metabolism is what protects our muscles from catabolism, as metabolised intracellular fatty acid is converted into acetyl-CoA for subsequent utilization for energy. This has the effect of sparing your glucose and protein stores.
Growth hormone response to exercise depends on the severity of the exercise. Prolonged intensive exercise causes GH levels to increase, along with glucagon, and a reduced level of insulin in the blood. It is important to note that the more adverse the condition and the harsher the exercise, the more GH is produced. This is found to be the case in resistance or weight training rather than in aerobic training.
One study observes the GH response to sprint and endurance athletes. In this study, 23 highly-trained sprint (100-400m) or endurance (1,500-10,000m) athletes were tested for GH levels after a performance of 30s sprint. There was a marked GH increase for all athletes, but the sprint-trained athlethes has 3 times greater GH response compared to endurance-trained athletes. The sprint group reach their peak GH levels 20-30 minutes after exercise, while the endurance group reached its peak 1-10 minutes post-exercise. What is surprising is that the GH levels of the sprint group remains 10 times the baseline after one hour post exercise. The study concluded the high intensity response to GH, and have attributed it to a combination of metabolic responses such as lactic acid production, serum pH, ATP depletion, low serum glucose, oxygen deficit, or other factors.
The availability of blood levels of carbohydrates modulates the GH response to exercise. In one study, administration of glucose deters GH production, while carbohydrate deprivation exagerrates the response.
GH secretion is also influenced more with maximal training rather than submaximal training. Also GH production varies depending on the muscle group that is exerted. Surprisingly, greater production is achieved in smaller muscle groups (e.g. arms) than in bigger muscle groups (legs).
Overall, GH levels as a result of exercise has tremendous benefits to our health. Whether your goal is to attain a leaner look or to build muscles, the presence of GH allows these anabolic effects to take place.
October 31, 2012
- Mauro G. Di Pasquale. Amino Acids and Proteins for the Athlete: The Anabolic Edge, 2nd Edition. CRC Press