The effect of resistance training with restricted blood flow on serum levels of hormones related to strength and muscle mass size

Dissertation for Master's Degree

Abstract

The general purpose of this research is to investigate the effect of low-intensity resistance training with restricted blood flow on the serum levels of growth hormone, cortisol, testosterone and IGF-1 in young men. 30 healthy young men with an age range of 19-24 years who volunteered to participate in the study were selected as a statistical sample and were randomly assigned to three groups of low-intensity resistance training BFR (with an intensity of 20% of 1RM, 1 set of 30 repetitions and 2 sets of 15 repetitions), intense resistance training without BFR (three sets of 10 repetitions with an intensity of 80% of 1RM) and control. Both training groups performed squat and knee extension exercises three days a week for three weeks. The serum levels of cortisol, testosterone, GH and IGF-1 were measured before and after morning exercise and in the fasting state. ANOVA statistical test was used to compare the mean difference of the variables. The level of statistical significance was p<0.05. Data analysis showed that after three weeks of training, there was a significant difference between the serum levels of GH, IGF-1 and cortisol in the BFR training group, the resistance training group without BFR and the control group (p<0.05). However, no significant difference was observed between the serum testosterone levels of the three groups at the end of the study. In general, it can be concluded that short-term BFR low-intensity resistance training can cause more changes in anabolic-catabolic hormones compared to resistance training without BFR in young men.

Key words: blood flow restriction, growth hormone, insulin-like growth factor, cortisol, testosterone

Introduction

Resistance training is one of the essential and important components of most sports programs. These exercises are also very important in the rehabilitation programs of athletes after physical injuries. The effectiveness of these exercises in increasing muscle strength, treating sports injuries, and preventing muscle mass loss due to aging and inactivity depends on the amount of exercise [2,1]. Based on research evidence, high-intensity resistance training, i.e. approximately 80% of one repetition maximum [1] (1RM), optimally increases muscle strength [1]. It has also been reported that resistance training with 6-12 repetitions and with an intensity of 70-85% of 1RM increases strength and muscle size or hypertrophy [2] [3]. The American College of Sports Medicine [3] (ACSM) has also suggested resistance training with a load greater than 70% of 1RM for functional and morphological adaptations (appearance) of the muscle [5,4]. Therefore, one of the main goals of using different methods of resistance training is to increase maximum strength and muscle size or hypertrophy. Based on the results of the studies, high-intensity exercises (80-90% 1RM) with low repetitions (2-8 repetitions) and long rest intervals (2-5 minutes) are suitable for increasing maximal strength, and moderate-to-high intensity exercises (70-80% 1RM) with high repetitions (8-15 repetitions) and shorter rest intervals (30 seconds to 2 minutes) are suitable for increasing muscle size or hypertrophy [7,6]. However, different results have been reported in terms of short-term and long-term adaptations of hormones related to increasing strength and muscle mass size after different training protocols. The intensity of 70-80% of 1RM of resistance training, which is reported to be the appropriate intensity for increasing muscle strength and size, is also necessary for changes in hormones related to increasing muscle strength and size [8]. Therefore, it seems that high-intensity resistance training is associated with many changes in anabolic-catabolic hormones. The balance between catabolic hormones such as cortisol and anabolic hormones such as testosterone and dihydroepiandrosterone[4] (DHEA) has an important application in the performance and recovery periods after resistance training[10,9]. Cortisol is a catabolic hormone and the most important anti-stress hormone in the body. But its increase in the long term causes problems, the most important of which are problems related to the immune system and protein destruction[11]. The results of studies show that cortisol changes depend on the intensity and duration of training [9].

The growth rate of muscle cells depends on the activity of some hormones, including growth hormone [5] (GH), insulin, insulin-like growth factor-1 [6] (IGF-1) and steroid sex hormones, especially testosterone [12].Research results regarding the acute hormonal response to resistance training show that anabolic hormones such as growth hormone and testosterone, which are very important and vital in tissue growth and regeneration, increase during and after resistance training [13]. These hormones play an important role in increasing protein synthesis. Therefore, the improvement of some factors of physical fitness in teenagers is attributed to the increase in the level of these hormones [14]. In this regard, Kramer [7] (2004) stated that if the rest interval between resistance training periods, which is performed with 80% of 1RM in 6 periods and 10 repetitions in each period, is less than 1 minute; It can cause a significant increase in the secretion of growth hormone and testosterone [15]. Testosterone is an anabolic hormone that stimulates protein synthesis and plays a very important role in the growth and maintenance of muscle tissue [16]. Growth hormone is one of the most important hormones in the body, which together with a group of other hormones affects metabolism and is necessary for maintaining body weight and protein production in adults. Normal growth has been proven to be directly related to the plasma concentration of somatomedin-C [8] or insulin-like growth factor IGF-1 [17]. The secretion of GH and IGF-1 is effective in increasing muscle size, and a direct relationship between the concentration of these hormones and the increase in muscle strength and size has been observed [18].

Many studies have been conducted regarding the effect of growth hormone on increasing maximum strength and increasing muscle size, and in most of them, a direct relationship has been observed between the concentration of this hormone and the increase in strength and muscle size. In adults, growth hormone facilitates protein synthesis. This action is carried out by transferring amino acids through the cell membrane, and they lead to the stimulation of increased production and the activation of cellular ribosomes. [19].

IGF-1 hormone is another dependent variable of muscle cell size. The IGF system is a group of peptides and proteins of the same family that play a pivotal role in growth and metabolism. As the most important member of this family, IGF-1 exerts strong growth effects on muscle and bone tissue. This peptide also mediates insulin-like actions, especially in muscle tissue, and circulates in the plasma in the form of a combination with one of its six binding proteins [20]. Research evidence shows that there is a regulatory-feedback relationship between growth hormone and the IGF-1 system, whereby the secretion of growth hormone increases the hepatic production of IGF-1. In addition to these special effects, IGF-1 mediates some of the actions of GH, especially in muscle and bone tissue, and circulating IGF-1 levels inhibit GH secretion as a negative feedback [21]. Researchers believe that GH indirectly participates in growth stimulation. In this way, GH causes the liver (and to a much lesser extent other tissues) to make some small proteins called somatomedin, which has a very strong effect in increasing the growth aspects of the tissues. GH goes through the bloodstream to the liver and other peripheral tissues, where IGF-1 is produced. This hormone has anabolic effects and causes tissue growth [22].

Abstract

The aim of the study was to investigate the effect of blood flow restricted resistance training on serum hormone levels in relation to muscle size and strength in young men. A total of 30 healthy young men (aged 19-24 yrs) were volunteered for this study. Subjects were randomly assigned into three groups: a low intensity blood flow restricted resistance exercise (BFR) group (20% of 1-RM, 3 sets of 15 reps), a traditional high intensity resistance exercise without blood flow restriction (HI) group (3 sets of 10 repetitions at 80% of 1-RM) and a control group. Both BFR and HI groups trained 3 days per week for 3 weeks for knee extension and squat exercises. Fasting serum cortisol, growth hormone (GH), IGf-1 and testosterone levels were measured in the morning pre and post exercise sessions. Data were analyzed with one-way ANOVA at the level of p<0.05. After 3 weeks, serum GH, IGF-1 and cortisol levels changed significantly between three groups (P<0.05). However, there were no significant changes in serum testosterone between them (P?0.05)