Sport Physiology

Sport Physiology

The Effect of Hydroxy-Beta-Methylbutyrate and Caffeine Supplementation on Growth Hormone Levels Following Resistance Exercise in Obese Women

Document Type : Research Paper

Authors
Kazhan Rostami 1
Awat Khorang 1
Hassan Faraji 1
Mohammad Rahman Rahimi 2
1 Department of Physical Education and Sport Sciences, Marivan Branch, Islamic Azad University, Marivan, Iran
2 Department of Physical Education and Sport Sciences, Faculty of Humanities and Social Sciences, University of Kurdistan, Sanandaj, Iran
10.22089/spj.2025.17863.2361
Abstract
Background and Purpose
Growth hormone (GH) is a potent anabolic hormone that affects multiple systems in the body and plays an important role in lipid metabolism in various locations such as the liver, skeletal muscle, and visceral adipose tissue. Exercise is a potent physiological stimulus for GH secretion, and both aerobic and resistance exercise result in significant, acute increases in GH secretion. The administration of exercise as a stimulus to elicit a GH response in obese individuals is of considerable importance, as it may offer a non-pharmacological approach to reduce adipose tissue deposits and increase lean muscle mass. However, studies have shown that resistance exercise is less able to increase circulating GH in obese individuals than in normal or lean individuals. B hydroxy-b-methylbutyrate (HMB), a metabolite of the amino acid leucine, has been shown to promote strength and lean muscle mass when supplemented in conjunction with resistance training. HMB administration has been shown to increase GH and IGF-I mRNA levels in in vitro and in vivo models, and acute and chronic HMB administration has been reported to increase serum GH levels in normal individuals. The higher bioavailability may rationalize acute supplementation with HMB as a means to enhance the anabolic response resulting from heavy resistance training. Some studies have reported that caffeine is associated with a decrease in GH levels, while others have reported an increase. Our secondary aim was to investigate the effect of caffeine consumption on GH levels after resistance exercise in obese individuals. Therefore, the present study investigated the effect of HMB and caffeine supplementation on GH levels following a single session of resistance exercise in obese individuals.
Materials and Methods
The statistical population consisted of inactive obese women aged 28 to 44 years and without any disease (diabetes, cardiovascular disease, motor disorders, etc.). Among 16 eligible volunteers, 11 volunteers were selected by simple random sampling. All subjects gave their written consent before their inclusion in the study. At least ten days before the experiments, anthropometric and 1-repetition maximum (1RM) measurements were collected, and the subjects were familiarized with the exercise scheme. Percent body fat was calculated by using the equation of Brozek et al. Subjects performed a resistance exercise test in four conditions of placebo (P), HMB (H), caffeine (C), and a combination of HMB and caffeine (HC) in a within-group design with reciprocal balancing. Subjects in condition H consumed 3 g of HMB, 6 mg per kilogram of body weight of caffeine in condition C and condition HC in a combined amount of both conditions, and in condition P also consumed maltodextrin. HMB was consumed 30 minutes and caffeine one hour before the test. The interval between test sessions was one week. Subjects were engaged in a standardized pre-prepared breakfast for 15 minutes in the morning of each session. Blood samples were taken from the subjects after 180 minutes of rest. After consuming the relevant supplement and after the required time, they started to perform sports activities with a predetermined intensity. The next blood sample was taken immediately after the exercise and the third blood sample was taken 30 minutes after the end of the exercise. The serum samples were placed at room temperature for 20min after being transferred to the tubes. The serum was obtained after 20min of centrifugation (3,000 rpm, 4°C) and stored at -20°C until further analysis. Two-way analysis of variance with repeated measures and Tukey's post hoc test were used to examine the differences within and between groups with a prespecified experimental type I error rate of 0.05 was used to maintain a type I error rate of 0.05. All calculations were analyzed with SPSS21 software at a statistical level of p<0.05. Normal distribution for all variables was verified with the Shapiro-Wilk test. For all repeated-measures ANOVAs, Mauchly’s test of sphericity was performed to assess the equality of variances between groups. All the data were expressed as means ± SD, and the statistical significance was accepted for p<0.05.
Findings
All subjects completed the acute resistance exercise session. The data had a normal distribution, and the assumption of homogeneity of variance was violated. In different test conditions, the difference in mean GH levels was significant only in condition H (F=23.27, p=0.001), in which GH levels were significantly higher than resting levels (p=0.001) and 30 minutes after exercise (p=0.003). GH levels immediately after exercise were higher than levels of this hormone in other conditions (p<0.05). GH levels in other conditions including conditions C, P and HC did not change significantly (p>0.05). Changes in mean insulin and glucose levels in different test conditions were not significant (p>0.05).
Conclusion
In summary, these results appear to be the first study to demonstrate that three grams of HMB can significantly increase GH following acute, high-intensity resistance exercise compared with placebo in obese women. This finding makes important contributions to our understanding of how HMB affects endocrine function in obese individuals. Caffeine does not appear to make a difference in circulating GH levels following resistance exercise.
Article message 
Considering our results regarding the lack of GH increase in obese women during resistance exercise but its increase with HMB consumption, it seems that HMB consumption before resistance exercise can increase GH in obese individuals. On the other hand, caffeine, either alone or in combination with HMB, has no effect on GH levels in obese individuals.
Funding
The present study did not receive any financial support.
Authors’ Contributions
All authors contributed to the design, implementation, and writing of all parts of this study.
Conflicts of Interest
The authors declare no conflict of interest.
Acknowledgement
We would like to thank the subjects of the present study.
Keywords
Obesity
HMB
trimethylxanthine
GH
acute exercise
Subjects
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Sport Physiology
Volume 16, Issue 64
Summer 2025
Pages 91-72

  • Receive Date 09 March 2025
  • Revise Date 16 June 2025
  • Accept Date 05 July 2025