Aerobic Exercise Increases Release of Growth Hormone in the Blood Circulation in Obese Women

. Physical exercise is one of the modulators in increasing the release of growth hormone (GH) levels in blood circulation, but the effective exercise model for obese subjects is still being debated. Therefore, this study aims to prove the effect of aerobic exercise on increasing the release of GH levels in the blood circulation in obese women. A total of 20 obese adult women, aged 21.00 ± 1.08 years were selected to be subjects in the study and were given one aerobic exercise intervention by running on a treadmill at moderate-intensity (60-70% HR max ) for 40 minutes. The ELISA method was used to measure the release of GH levels in all samples (pre-and post-exercise). Statistical analysis in this study used an independent sample t-test with a significant level of 5%. The results showed that the release of GH levels in the blood circulation was found to be higher in post-exercise compared to pre-exercise after one session of aerobic exercise (484.92±128.29 vs 892.63±273.54 pg/mL; p=0.001) and has a large effect size with a Cohen's d value of 1.909. GH levels in the post-exercise blood circulation in the aerobic exercise group (Exr) were also found to be higher than the GH levels in the control group (Ctr) (892.63±273.54 vs 542.97±140.01 pg/mL; p=0.003) and has a large effect size with a Cohen's d value of 1.609. This study proves that one session of aerobic exercise with moderate intensity increases the release of circulating GH levels in obese women. Therefore, aerobic exercise with moderate intensity can be used as an alternative therapy option to increase the release of circulating GH levels in individuals with obesity.


Introduction
The prevalence of obesity in the world continues to increase due to high food intake followed by low physical activity (Alvarez et al., 2020) and is dominated by women compared to men (Blüher, 2019).Physiologically, obesity has become a risk factor that may affect the release or regulation of growth hormones (Høgild et al., 2019).Hejla, Dror, Pantanowitz, Nemet, & Eliakim (2022) reported that GH secretion was lower in overweight and obese individuals than in normal weight individuals.The association of obese individuals with low growth hormone levels was also reported by Savastano, Di Somma, Barrea, & Colao (2014) Obesity causes a decrease in GH secretion, resulting in increased fat mass, decreased lipolysis, and decreased insulin sensitivity, leading to metabolic disorders (Høgild et al., 2019).Obesity stands as a primary risk factor for mortality (Hruby & Hu, 2015).Therefore, decreased GH secretion in obese individuals may lead to an increase in serious health problems (Misra et al., 2008).Obesity is generally caused by a long-term imbalance between calories consumed and calories expended (Camacho & Ruppel, 2017;Solis-Urra et al., 2019).Promoting a less sedentary lifestyle and incorporating regular physical activity are key factors in preventing the development of obesity (Romieu et al., 2017;Dávila Grisalez, Mazuera Quiceno, Carreño Herrera, & Henao Corrales, 2021).
Exercise is promoted as an appropriate and effective approach to increase GH-mediated energy expenditure to prevent the development of obesity (Rejeki et al., 2023;Strasser, 2013).Exercise can also improve metabolic health by increasing physical performance, lipid and glucose metabolism (lipolysis and insulin sensitivity), and weight maintenance (Wang et al., 2020;Dávila Grisalez, Mazuera Quiceno, Carreño Herrera, & Henao Corrales, 2021), so it can improve metabolic health (Dourida et al., 2019).Exercise is also known to prevent deficiency of GH secretion in overweight and obese individuals (Al-Samerria & Radovick, 2021).This finding was supported by research conducted by Sugiharto, Merawati, Pranoto, & Susanto (2022), which demonstrated that a single session of endurance training at an intensity of 60-70% HR max performed for 30-35 minutes on a treadmill increased GH secretion in obese women.Research conducted by Berry, Hubal, & Wideman (2018) also reported that treadmill exercise in moderate intensity performed for 60 minutes increased the release of GH levels in healthy and prediabetic subjects with obesity (BMI = 32.1±4.0kg/m 2 ).However, research by Sasaki et al. (2014) found no change in GH response after 4 weeks (3 days/week, 12 sessions total) of high-intensity interval training (10 sets of 1 min pedaling at 85% VO 2 max with a 30 s rest between sets) in sedentary men.In another case, research conducted by Hejla, Dror, Pantanowitz, Nemet, & Eliakim (2022) a single session of the Wingate anaerobic test (WAnT) with 10 bouts of 15-second cycling separated by 1 minute of rest significantly reduced GH levels in children with overweight and obesity compared with those with normal weight.Meanwhile, a study by Deemer et al. (2018) used a crossover design in five young women to compare the effects of high-intensity interval exercise (HIE) (four 30-s "all-out" sprints with 4.5 min of active recovery) and 30min continuous cycling with moderate-intensity continuous exercise (MOD) on GH secretion.The results showed that a single bout of HIE increases 12.5 h GH secretion compared to the sedentary control condition and was not different from MOD exercise.
Based on these findings, it is still debatable which exercise model is effective in increasing the release of GH levels in obese subjects.Therefore, the primary objective of this study is to demonstrate the effect of aerobic exercise at moderate intensity on increasing the release of GH levels in the blood circulation, especially in obese women since the prevalence of obesity is higher in this population than in men.The results of this study can strengthen the existing research that is still being discussed and used as a potential non-pharmacological treatment option to enhance the release of GH levels in the blood circulation of individuals with obesity, thereby improving their metabolic health.

Materials and methods
This research adopts a true experimental design with a pre-test and post-test control group.A total of 20 obese adult women, age 21.00 ± 1.08 years, with body mass index (BMI) 29.59 ± 1.24 kg/m 2 (according to Asia-Pacific guidelines), percentage of body fat (PBF) 45.17±2.90%, blood pressure (systolic: 113.80 ± 3.65 mmHg; diastolic: 75.25 ± 3.96 mmHg), resting heart rate (RHR) 72.15 ± 6.08 bpm, oxygen saturation (SpO 2 ) 97.60 ± 1.14 %, maximum oxygen volume (VO 2max ) 27.43 ± 2.56 mL/kg/min, and fasting of blood glucose (FBG) 90.50±5.29 mg/dL were selected to be subjects in this research.The selected subjects had no history of chronic diseases, smoking, or alcohol consumption.It was also confirmed that all subjects were not active in sports activities and were not enrolled in any weight loss program that involved the use of medication or dietary modifications.Before the study was conducted, all selected subjects were given a detailed description of the research objectives and methods which was clearly and consciously communicated verbally or in writing, and then all subjects completed and signed an informed consent form.The day before the test, all subjects were instructed to get enough sleep (7-8 hours/night) and fast overnight for 10-12 hours.During the research, water intake was monitored to maintain hydration.The test was carried out in the morning on the 5-7 th day of the menstrual cycle, to control hormonal status.
The subjects with matching BMI were randomly assigned to participate in experimental: the control group (Ctr; n = 10), and the aerobic exercise group (Exr; n = 10).The calculation of the sample size using the Higgins & Kleinbaum formula (1985) with reference values from previous similar studies so that a minimum sample size was obtained and 20 subjects were taken (Sugiharto, Merawati, Pranoto, & Susanto, 2022).All procedures performed in this research were approved by the Health Research Ethics Committee, Faculty of Medicine, Airlangga University (No. 283/EC/KEPK/FKUA/2021).
The aerobic exercise intervention program was implemented and supervised by professional staff from Pusat Pelayanan Kesehatan Olahraga (PPKO) in Malang City, East Java, Indonesia, to minimize the occurrence of incorrect use of the treadmill and the risk of injury.Aerobic exercise was performed on a treadmill in a single session at an intensity of 60-70% of HR max , following the research by Pranoto et al. (2023), but with a duration of 40 minutes.Warm-up and cool-down were performed by brisk walking on the treadmill at an intensity of 50% HR max for 5 minutes each (Rejeki et al., 2023).HR max was determined using the following formula: HR max -age in years (220 -age in the year) (Santos et al., 2019;Susanto, Sugiharto, Taufiq, Pranoto, & Purnomo, 2023).Heart rate was monitored during aerobic exercise using the Polar H10 heart rate sensor (Pranoto et al., 2023).The intervention would be stopped if abnormal physical signs were detected, such as shortness of breath, rapid increase in heart rate, dizziness, nausea, pale face, and muscle cramps.The environment used for the research site has a room temperature of 26 ± 1°C with a humidity level of 50 -70% (Rejeki et al., 2023).During the intervention, the subjects did not experience any problems or difficulties that interfered with the completion of the aerobic exercise session.Details of the aerobic exercise intervention program and the blood sampling procedure are shown in Figure 1.
The normality and homogeneity test was performed using the Shapiro-Wilk and Levene's tests.The paired sample t-test was used to determine differences in GH levels before and after exercise in each group, while the independent sample t-test was used to determine differences in GH levels between the control group and the aerobic exercise group.Statistical analyses were performed at a 5% significance level, and all values are presented as the mean ± standard deviation (SD).The Statistical Package for The Social Sciences (SPSS) software was used for all statistical analyses.

Results
Table 1 presents the basic data on the characteristics of the subjects in the control group (Ctr) and the aerobic exercise group (Exr) and the result was no significant difference between the groups.The results of growth hormone (GH) level analysis in both groups are shown in Figure 2-3.Figure 2 shows the mean of GH levels between preexercise vs. post-exercise on Ctr (533.98±137.49vs. 542.97±140.00pg/mL; p=0.714), and Exr (484.92±128.29 vs. 892.63±273.54pg/mL; p=0.001) has a large effect size with a Cohen's d value of 1.909.Meanwhile, Figure 3 shows the difference in GH levels between Ctr vs. Exr at pre-exercise (533.98±137.49vs. 484.92±128.29 pg/mL; p=0.420), at post-exercise (542.97±140.00 vs. 892.63±273.54pg/mL; p=0.003) has a large effect size with a Cohen's d value of 1.609, delta

Discussion
Growth hormone (GH) is a polypeptide consisting of 191 single-chain amino acids and the human GH gene is located on chromosome 17q22 and GH synthesis occurs in somatotropic cells in the anterior pituitary gland (Olarescu et al., 2019;Kraemer, Ratamess, & Nindl, 2017;Guyton & Hall, 2014;Greenstein & Wood, 2011).One of the factors that inhibit GH synthesis is obesity (Dichtel et al., 2014).In the presence of obesity, various metabolic disorders such as increased insulin levels (hyperinsulinemia), decreased adiponectin levels (hypoadiponectinemia), increased leptin levels (hyperleptinemia), decreased ghrelin hormone production, and increased free fatty acids (FFA) levels manifest and lead to the suppression of GH secretion from the pituitary gland (Savastano, Di Somma, Barrea, & Colao, 2014).Previous research conducted by Stanley & Grinspoon (2015) found significant differences in the release of circulating GH levels in overweight and obese individuals as opposed to normalweight individuals.Normal-weight individuals have higher post-exercise GH levels than overweight and obese individuals.The results of this study confirm that overweight and obesity are factors that inhibit the release of GH levels in the blood circulation, so GH levels are lower in overweight and obese individuals than in normal-weight individuals (Sabag, Chang, & Johnson, 2021).Exercise is considered a non-pharmacological approach that can be used to increase the release of GH levels into the blood circulation (Oliver et al., 2010).The study conducted by Gough, Castell, Gatti, & Godfrey (2016) showed that aerobic exercise in the form of running on a treadmill for 40 minutes at a pace 5% below the lactate threshold speed significantly increased serum GH levels.Our results demonstrated that aerobic exercise performed for 40 minutes at an intensity of 60-70% HRmax significantly increases the release of GH levels in blood circulation.This increase is consistent with the research of Sauro & Kanaley (2003) who reported that GH levels were significantly increased in young women after 10 minutes of treadmill and cycling exercise at an intensity of 75% VO 2 peak.
The results of this study, shown in Figure 3, demonstrate a significant increase in circulating GH levels after aerobic exercise compared to the control group (no exercise intervention).These findings are consistent with a study by Mannerkorpi et al. (2017), which showed that a 15-minute session of acute moderate-intensity exercise using an ergo cycle significantly increased GH levels in women with a BMI 28.2 ± 5.3 kg/m 2 .The increase in GH levels is predicted to be caused by the intervening factor of aerobic exercise which increases energy demand and metabolism.During exercise, the body requires glucose as the main source of energy, which is derived from carbohydrates and fats that are converted into energy (adenosine triphosphate) (Guyton & Hall, 2014).This condition will cause a decrease in blood glucose levels (hypoglycemia) as a result of ingestion and use in the body's cells.The decrease in blood glucose levels causes stimulation of the central nervous system (CNS) to activate the hypothalamus which stimulates GhRH and somatostatin to increase GH secretion in blood circulation (Wood, Clow, Hucklebridge, Law, & Smyth, 2018).
The release of GH secretion into the blood circulation is predicted to remain high for 24 hours after exercise and will gradually decline to baseline conditions in obese women (Sugiharto, Merawati, Pranoto, & Susanto, 2022).This state is very beneficial because it can increase basal metabolism, thus increasing energy expenditure (Al-Samerria & Radovick, 2021), and has implications for reducing fat mass (Dinas, Markati, & Carrillo, 2014).The results of this study indicate a significant role for aerobic exercise as a breakthrough non-pharmacological obesity therapy in reducing the prevalence of obesity (Gar et al., 2020).Our research strengthens previous studies regarding the positive effects of aerobic exercise on GH levels in obese women.However, there are several other factors that increase the release of GH secretion in blood circulation, including gender, age, puberty, exercise, diet, fasting, sleep, and body composition.This study still has some limitations, so further research is recommended to consider these factors, using a larger sample as well as involving male subjects is necessary to obtain best results.It is also advisable for future research to contrast different methods and mediums because can influence the hormonal response of the population.In addition, do not lose sight of the covariate variables because that can affect the dependently.

Conclusion
This study proves that a single 40-minute session of aerobic exercise, performed at an intensity of 60-70% HR max , can increase the release of growth hormone levels in the blood circulation in obese women.Therefore, aerobic exercise can be recommended as a modulator in increasing the release of growth hormone levels in the blood circulation to maintain the balance of glucose metabolism, increase lipolysis, and improve insulin resistance in obesity.

Table 1 .
Body mass index; DBP: Diastolic blood pressure; FBG: Fasting of blood glucose; PBF: Percentage of body fat; RHR: Resting heart rate; SBP: Systolic blood pressure; SpO2: oxygen saturation; VO2max: maximum oxygen volume.Ctr: Control group; Aerobic exercise group.Values are expressed as mean ± SD.Independent sample t-test was used to determine the p-Value.