Abstract
This paper discusses how exercise stimulates the release of growth hormone. Older people tend to have lower levels of the hormone. As a result, mechanisms have been formulated to help deal with the deficiency which includes inducing the growth hormone into the individual’s body. This, therefore, leads to the discussion of the exact mechanism through which the growth hormone facilitates exercise, maintains growth and repair of worn out muscles or even reverses the aging process among the aged. Also, the functions of IGF-I binding proteins during exercise and its importance in aiding the release of the GH is elaborated. As exercise plays a very important role in the production of the HGH, the paper also elaborates how the protein turnover is effected during the process, which leads to an increase in the mitochondrial and myofibrillar proteins that are located in the skeletal muscles. After exercise, it is important to note that the high metabolism depletes the muscle glycogen stores. As the main priority after that is to replenish the body with adequate glycogen, the body is stimulated to release the growth hormone which later leads to the utilization of the existing lipids of the skeletal muscles in the process of recovery. The roles of the binding proteins and the effect of the receptors of the growth hormone on the downstream signaling pathways are also reviewed in this research paper.
The human growth hormone is produced in a rhythmic form from the human body. The substance revolves around the circadian rhythm. It stimulates the growth and development of body tissue with its maximum effect being experienced among the young individuals. There are other several factors that contribute to the release of the hormone including sex, age, and level of exercise. In other words, the hormone regulates the activities in a human body during exercise. There is a relationship between the release of Growth Hormone and physical exercise.
Definition
Growth Hormone
Growth Hormone is also known as the Human Growth Hormone or somatotropin. It is secreted by the pituitary glands, with the neurosecretory nuclei of the hypothalamus regulating its release. The release of the hormone is determined by the balance of the growth hormone-inhabiting hormone and the growth-hormone-releasing hormone. GH is a peptide hormone whose functions include:
Cell reproduction.
Stimulating growth.
Partaking in cell regeneration in animals, including human beings.
Stimulating production of insulin-like growth factor I.
The hormone is a single-chain polypeptide that is synthesized by the somatotropic cells found in the pituitary glands. It is also a stress hormone that increases the concentration of the free fatty acids and glucose. There are cases where the human growth hormone is combined with other compositions to form somatotropin, which is used in the treatment of children with growth disorders.
The growth hormone exists in the pituitary gland and also in the blood in several forms which include the 22 kDa GH, which has 191-amino acids and also the 20 kDa form which lacks approximately 14 amino acids. Despite this, the latter manages to bind to the growth hormone receptor and also ends up performing similar functions as the former.
The HGH also deals with cases of adult growth hormone deficiency. Although it has been banned by the NCAA and other sports bodies, some athletes still use the hormone to increase their endurance since it has an anabolic effect. Apart from being modified for use for the human beings, the growth hormone is also used in the field of agriculture. There are plans to use the hormone in livestock production. The focus in this research paper though is growth hormone in the human beings.
Physical Exercise
Physical exercise includes activities that enhance physical fitness and the overall body health. The exercise aims at ensuring that muscles and cardiovascular systems are maintained. Some of the physical exercises that boost the level of the growth hormone include the back squat and the deadlift. Back squats for example lights up the body muscles by generating a great demand for the HGH, which helps build a stronger lower body and leg muscles.
Growth hormone releasing hormone
Another name for this hormone is somatocrinin. The primary role of this hormone is to regulate the synthesis and the secretion of the human growth hormone. It is produced by the hypothalamus and binds with specific receptors on the somatotrophs of the pituitary to stimulate the release of GH.
Somatomedin
This is another name for the insulin-like growth factor I (IGF-I). These hormones enhance cell growth and division when the growth hormone is stimulated. The hormones are produced by the liver when the growth hormone acts on a particular tissue. By acting directly on the anterior pituitary gland, the somatomedin inhibits the release of the growth hormone. In return, the somatostatin hormone is secreted from the hypothalamus.
Somatostatin
Somatostatin suppresses the release of the human growth hormone. It is produced in the hypothalamus and other organs such as the central nervous system, the pancreas and the intestinal track. Apart from inhibiting the release of the Growth Hormone, it also acts on various tissues to inhibit the release of hormones such as glucagon and insulin.
Insulin-like Growth Factor-Binding Protein
The IGFBP are carrier proteins for the insulin-like growth factor 1(IGF-I). The binding protein attaches to the IGF-I in the ratio of 1:1. The process sometimes takes place in the liver, which allows the growth hormone to act on the liver to produce more IGF-I (Taylor, Thompson, Clarkson, Miles, & De Souza, 2000). The IGFBP have a high affinity for the IGF-I and IGF-II just as the ligands have an affinity for the IGF-IR. The binding proteins help in increasing the half-life of the IGFs in the body tissues.
Metabolism and Physical Exercise in the Axis
The growth hormone effects are mediated through the autocrine and the endocrine mechanisms (Gatti, De Palo, Antonelli, & Spinella, 2012). The effects are anabolic and insulin sensitizing. The GH/IGF-I system is comprised of the GHBP and the IGFBP. The axis is of great importance when it comes to modifying the organism in terms of physical exercise. Any physical activity stimulates the anabolism process in various tissues, most especially muscular adjustments. There is a correlation between muscle strength, the level of exercise tolerance, the speed of walking and the concentration of IGF-1/ IGFBP-3. Research, however, shows that there is an inverse correlation between chronic exercise responses and IGF-I concentration (Pharmacol, 2008).
The insulin growth factor-I is a significant mediator of the growth hormone. It has metabolic effects when under the endocrine and autocrine mechanisms. The main regulator of the synthesis of the growth factor and the binding factor is the growth hormone itself, found in the human plasma. An increase in the synthesis of the IGF-I (with the involvement of the IGFBP) signifies that the skeletal muscles are getting a stimulatory impact from any physical exercise. In some cases, physical exercise does not have a direct association with the circulation of IGF-I. For example, exercise can exert muscle strength by deriving the autocrine or the endocrine mediators (Nephrol, 2000).
Spontaneous GH Secretion
As mentioned, the process of secreting the growth hormone is pulsatile and hence, there are around thirteen pulses released per day. The greatest pulse happens approximately after one hour of sleep. Females, however, have higher levels of the Growth Hormone.
How HGH Production is Stimulated in Response to Exercise
The human growth hormone is secreted in a pulsating design after the circadian rhythm. The production is initiated by the physiological stimuli with the best example being sleep and exercise, which are non-pharmacological. The effects that the growth hormones have on the human body are mainly anabolic. The hormone interacts with a receptor to perform a function, just like any other protein.
The mechanisms through which exercises ensure the release of the hormone include, direct stimulation by catecholamines, neural input, changes in the acid-base balance and lactic and nitric oxide stimulation. Candidates displaying mechanisms such as afferent stimulation and the lactate and nitric oxide are the best. To define how best different exercises affect the exercise-induced growth hormone, it is important to understand how the various exercises affect the level of the human growth hormone.
Resistance Training
This training provides a great room for exercise-induced growth hormone release. Load and frequency determine how much of the hormone is produced. Growth hormone during resistance training is mainly produced when the program in use cause the utilization of a large muscle group at the same time. The release of the growth hormone depends on the demand of the anaerobic glycolysis during the training. A resistance trainee should monitor their workout and ensure that they are lifting the correct loads within the correct resting periods to ensure that maximum growth hormone is produced during training.
Endurance Training
In this particular type of training, the release of the growth factor depends on the intensity, frequency, duration as well as the type of exercise. The greatest growth hormone release happens when the exercise is done above the lactate threshold level for at least ten minutes. The release occurs during the training and for the next twenty-four hours. This means that the optimal levels for the release are shorter but should be done severally at a higher intensity than the lactate threshold.
However, there are negative impacts if the endurance training is taken too far to the point the body can no longer endure. If the training takes a longer period, the level of the growth hormone decreases in the body leading to an increase in the level of cortisol. Cortisol is a hormone that breaks down body tissues.
For that reason, it is important to exercise with high-intensity during cardio training but at the same time ensure that one avoids overdoing it. Overtraining is dangerous as the body might fail to recover, which might lead an individual to the catabolic state. For an endurance trainer, therefore, they should take high-intensity interval training in in order to bring about the maximum production of the growth hormone. They should put into consideration the proper nutrition steps to manage their long session thus minimizing the chances of the body going into a catabolic state.
Exercises among Aging People
The human growth hormone has an effect on the aging people. As people age, the level of muscle mass reduces while that of the fat mass increases. This change consequently leads to an increased body fat percentage, which increases the risk of one acquiring different diseases. Since the growth hormone can increase the lean muscle and reduce the body fat, aging people have that option of injecting themselves with the growth hormone to reap its benefits (Godfrey, Madgwick, & Whyte, 2003).
Unfortunately, the effects are not completely positive for there are reported cases of impaired glucose tolerance. For this reason, most aging people find it unnecessary to inject their bodies with the growth hormone.
The only alternative is for the aging people to exercise more intensively than what is prescribed as normal for a person of their age. With this, the chronic growth hormone level increases and the aging person achieves the full benefits just like a young person.
Regulation of Muscle Mass by the Somatomedins
The growth hormone increases the levels of insulin-like growth factor, both in the hepatic and non-hepatic tissues, thus enhancing performance in an individual. The human body mass consists of forty percent of the skeletal muscle. Muscles have many functions in the body, which include breathing, locomotion, protection of internal organs and thermogenesis among other active roles; therefore, the muscle mass has to be regulated.
People such as body builders and power athletes are interested in increasing the mass of their muscles. On the other hand, there are those who aim at preventing the loss of muscles especially the elderly or people suffering from chronic illnesses such as cancer and HIV/AIDS. Exercise is the best tool that regulates the muscle mass. There is increased hypertrophy in the case of increased load on mass and atrophy in the case of disuse (Pharmacol, 2008).
The anabolic effect of testosterone among men makes them have greater muscle than women. This means that hormonal factors are as important in regulating the mass of the muscles. This is proven by the fact that body builders induce themselves with anabolic steroids, therefore, acquiring a muscle bulk. The growth hormone-somatomedins axis together with the insulin growth factor I play a very important role in regulating muscle mass, especially in growing children. The insulin growth factor, in this case, acts as a circulating hormone distinguishing itself from its role as an autocrine growth factor.
The growth hormone-somatomedin axis is a peptide hormone that is made and secreted by the somatotroph cells of the anterior pituitary gland. Secretion of the growth hormone occurs through a pulsatile process. The frequency and magnitude of the pulses produced by the secretion of the growth hormone depend on many factors including age, gender, diet, exercise, and adiposity.
The levels of the growth hormone serum also vary throughout the day (Pharmacol, 2008). Once the growth hormone receptor is expressed, the growth hormone acts on its designated tissues mostly the skeletal muscle. The binding of the growth hormone is caused by the dimerization of the growth hormone receptors while intracellular signaling involves the signal transducers, activators of the transcription pathway and Janus kinase.
For most tissues in the body, the growth hormone stimulates the synthesis of the insulin growth factor I. The liver is responsible for the production of the insulin growth factor serum. Administration of the growth hormone causes certain effects such as increased up-regulation of the proteins and IGF-I mRNA. The serum IGF-I is stable in healthy human beings as compared to the growth hormone. Serum IGF-I acts as a good indicator of whether there is a dysfunction of the growth hormone if they go above or below the normal age-corrected range. Other factors such as liver problems and malnutrition must be considered first before making this conclusion.
In general, the normal GH/IGF-I has a role to play in the development and maintenance of the muscle mass. People who lack the growth hormone receptor and the IGF-IR, tend to be deficient. It is, however, important to note that the administration of the somatomedins have no proven benefit for the muscle mass in the healthy human beings whose growth hormone function is considered normal. However, mechanisms that cause muscle adaptation are still complex. The somatomedins play an important role in the muscle development. Inducing one’s self with the growth hormone increases body performance due to increased lean body mass among the aging people.
Changes that Occur in the Muscles due to Production of the Growth Hormone
There is an increased synthesis of muscular proteins and reduced protein degradation among burnt individuals. However, for normal individuals, the vice versa occurs. There is also an increased IGF-I mRNA. An increase in the level of RNA is a symbol that there is an increased protein synthesis. Administration of the somatomedins causes accumulation of the myosin heavy chain proteins that causes increased muscle hypertrophy of the myofibrils. IGF-I stimulates the myogenic and mitogenic processes in the satellite cells.
Role the IGFBPs Play in Modulating the Growth Hormone in Response to Exercises
The axis that contains the growth hormone binding proteins and the IGF-I binding proteins (IGFBP) play an important role in the modification of a human form in case of the physical exercises. Any physical training involves the anabolism process, which especially affects the muscular adjustments.
There is a connection between the level of tolerance to exercise and IGFBP-3 concentration. The growth hormone regulates the synthesis of the IGFBP-3, which is the most abundant IGF carrier in the blood plasma. The increased IGF-I, whose career is the IGFBP-3, stimulates the skeletal muscle, which is a sign of muscle strength. Therefore, an increased synthesis of the insulin-like growth factor I mediates the stimulation of the skeletal muscle with the involvement of the IGFPB.
When one combines the IGF-I/IGFBP3 injection, there is a resultant increase in the protein balance in endurance-trained athletes. It is proven that these athletes experience reduced leucine oxidation when exercising – especially during a period of between one to four weeks. Protein sparing is, therefore, beneficial for the endurance athletes.
Factors influencing the release of exercise induced HGH
The release of the growth hormone during exercise is started by the inhibition of the release of somatostacin. This scenario takes place during low-moderate exercise. In a case of high exercise however, it is the increase in the secretion of GHRH that stimulates the release of the growth hormone. The following factors therefore describe the inhition of the somatostacin or the secretion of the GHRH, which are responsible for initiating the release of HGH during exercise (Artwelle & Wislon, 2008).
Blood Lactate and Acid-Base Balance
There is a confirmed relationship between the concentration of blood lactate and the concentration level of GH. However, there is no link that shows that blood lactate causes the release of GH. The relationship however arises during the production of hydrogen ions, whose increased concentration leads to an increased release of HGH. Hydrogen ions are released during the process of energy metabolism of lactate (Artwelle & Wislon, 2008).
Catecholamines
The secretion of catecholamines is stimulated by exercise. Its increased concentration consequently causes a trainer to either perfom endurance exercise, maximal sprinting or even resistance exercise. It is important to note that only increased energy metabolism can lead to higher exercise intensity, and therefore, this can be achieved through increased circulation of catecholamines. Their secretion also stimulates the release of the GH as they act directly on the hypothalamus (Artwelle & Wislon, 2008).
Core Temparature
An increase of the core temperature by one percent stimulates the release of the growth hormone. Exercise is known to rise the body temperature in an instance. There is therefore an important relationship between the rise in core temperature and the rate of change in the body levels of GH brought about by exercise. There is however a threshold beyond which the Growth Hormone is not released and this is at 38.0-38.50 (Artwelle & Wislon, 2008).
How Different Types of Exercise Regimens Result in Differential GH Activity
There are different factors considered that result to the different growth hormone activity.
Endurance
Endurance is the ability to exercise continuously without getting tired. With endurance, the production of the growth hormone depends on the duration, intensity, type of exercise and frequency. Growth hormone is produced rapidly at around this period and if the person exercising maintains the practice for a minimum of ten minutes.
Strength
When a trainer is strong, it means that their endurance is high. As a result, the individual has the ability to lift more loads at a high frequency. This mostly applies when it comes to resistance trainers. They usually should take short rest time, which will lead to the production of higher levels of GH from the body. In the case of endurance trainers, they should make sure that they take a balanced diet to gain more energy that is needed during the several exercising sessions to prevent their bodies from getting in to a catabolic state.
Balance
Muscle movement among other senses leads to normal balance during exercise. It is important for the endurance trainers to ensure that they exercise for longer hours between few time intervals. They should avoid overtraining. This will ensure that the lactate threshold is met, and the body will get back to its normal state within no time. Failure to balance will lead the body to get into a catabolic state.
Flexibility
Flexibility is achieved if a sports trainer has more lean muscle than fat muscle. With the lean muscle, the trainer has a higher endurance and the level of production of the growth hormone is, therefore, high. Flexibility enables a trainer to partake in both the resistant training and endurance training.
In conclusion, there is a relationship between the release of the Growth Hormone and physical exercise. Both high intensity and low intensity exercises have an influence though at varying levels. Its production is highest among young children and at puberty for this are the stages when a lot of growth takes place. Production is also at the peak during sleep and during physical training. There are also various factors that influence the release of exercise inguced HGH. The factors either cause a rise or a decline in the release of the hormone depending on their intensities. Although the release of the growth hormone is unending, it is high during some stages especially among children, in females and also during sleep. Inadequate GH among the older people can be replenished through induced mechanisms, especially for those individualsn who choose to remain active through exercise. This however has an effect on the glucose tolerance of the body and therefore, the person is expected to exercise morethan the normal rate. One way to deal with this is if they exercise more intensively than how the common people of their age group do.the production of the growth hormone happens in the liver but is secreted by the anterior pituitary gland through the regulation of the hypothalamus by the neurosecretory nuclei. The production is influenced by various insulin growth factors and is only inhabited by the somatostatin.
References
Artwelle, G. V., & Wislon, F. G. (2008). New Human Growth hormone. New York: Nova Science Publishers.
Gatti, R., De Palo, E., Antonelli, G., & Spinella, P. (2012, June 18). IGF-I/IGFBP system: metabolism outline and physical exercise. Retrieved March 10, 2016, from NCBI: http://www.ncbi.nlm.nih.gov/pubmed/22714057
Godfrey, R., Madgwick, Z., & Whyte, G. (2003). The exercise-induced growth hormone response in athletes. Retrieved March 10, 2016, from NCBI: http://www.ncbi.nlm.nih.gov/pubmed/12797841
Nephrol, P. (2000, July 14). Growth hormone axis overview--somatomedin hypothesis. Retrieved March 10, 2016, from NCBI: http://www.ncbi.nlm.nih.gov/pubmed/10912514
Pharmacol., B. J. (2008, May 26). Regulation of muscle mass by growth hormone and IGF-I. Retrieved mARCH 10, 2016, from NCBI: http://www.ncbi.nlm.nih.gov/pmc/articles/PMC2439518/
Taylor, J. M., Thompson, H. S., Clarkson, P. M., Miles, M. P., & De Souza, M. J. (2000). Growth hormone response to an acute bout of resistance exercise in weight-trained and non-weight-trained women. Journal of Strength and Conditioning Research, 14(2), 220-227.
