Introduction
Strength training causes several acute physiological responses and chronic adaptations that are very important for increasing muscular strength and hypertrophy. Some anabolic hormones, such as testosterone, have a critical role in the responses and adaptations to training (37). In fact, high-intensity and high-volume strength exercise is a powerful stimulus for an acute increase in the concentration of testosterone immediately after exercise (2,3,14,32). This response pattern has been associated with the increase in the synthesis of proteins during the rest period after the training session due to its influence on the increase in androgenic receptors in the muscle cell (5,29,50).
Some variables linked to the training session, such as intensity and volume (14,47), resting time (35), and involved muscle mass (20), influence the hormonal response to resistance exercise. In addition, studies have demonstrated that the level of training interferes in this response pattern (2,31,32), while others indicate there is no difference between trained and untrained individuals (1). At the same time, in relation to the pituitary-adrenocortical axis, some findings suggest that the increases of cortisol after resistance exercise may be lower in trained individuals (32), but no studies have investigated the influence of training on the dehydroepiandrosterone (DHEA) responses to this type of exercise.
Although the concentrations of total testosterone (TT) and free testosterone (FT) are seen to increase immediately after a strength training session (1,9,20,22,33), there is some controversy regarding alterations in their concentrations at rest after a period of training. Studies have evaluated young individuals and have demonstrated an increase in testosterone levels at rest after strength training (1,13,32,41,48). Nevertheless, other studies, including investigations involving middle-aged and elderly individuals, have found no differences in circulatory testosterone levels at rest after a period of training (3,19,20,27,46). Indeed, studies have investigated endocrine responses and adaptations to strength training (1,3,27,32) and comparisons of these responses between strength athletes and nonathletes (2). However, the literature contains very little information about possible endocrine adaptations to training in recreationally long-term strength-trained men. In a study by Ahtiainen et al. (1), no differences were observed between strength-trained athletes and untrained men in acute hormonal response to strength training. However, other studies have demonstrated a higher acute hormonal response to resistance exercise in strength-trained athletes compared to untrained subjects (2) and in subjects after a strength training period (32). Thus, information about the effects of strength training on acute hormonal response to exercise remains inconsistent. Moreover, no study has investigated the effects of many years of strength training on hormonal responses to resistance exercise in middle-aged men.
In the search for information on the possible role of the endocrine system in the adaptations to strength training in men, this study aims to investigate hormone concentrations at rest and induced by a training session for hypertrophy in middle-aged long-term trained and untrained men of the same age. Due to the higher testosterone values at rest (1,13,32,41) and induced by resistance exercise (2,32) observed in strength-trained subjects in other studies, the hypothesis was that the values of the measured anabolic parameters will be higher in long-term strength-trained individuals than in untrained individuals.
Methods
Experimental Approach to the Problem
The individuals visited the test center on 2 days. First, the individuals were interviewed regarding their medical history and physical activity. Their anthropomorphic characteristics were measured, and maximum dynamic strength tests were performed in 4 exercises. Twenty days later, the subjects were required to perform a resistance exercise session (i.e., a superset strength training protocol [SSTP]). Before (i.e., at rest) and after SSTP, blood was obtained to determine hormonal concentrations and sex hormone-binding globulin (SHBG).
Subjects
Twenty-one healthy, strength-trained and untrained middle-aged men (mean age, 40.6 ± 4 years) volunteered to participate in this study. Subjects were matched according to training status into 2 different groups: a strength-trained group (SG) (n = 10) and an untrained group (UG) (n = 11). All subjects were carefully informed about the potential risks and discomforts of the project and signed a written consent form before their participation in the study. This investigation was approved by the Ethics Committee of Federal University of Rio Grande do Sul. Table 1 shows the subjects' physical characteristics and maximal strength. There were no significant differences between the groups in age, body mass, or height. The SG had significantly higher values in percentage of lean body mass and lower values in percentage of fat mass (p < 0.05). Indeed, the SG had significantly higher values in all strength variables (p < 0.01).
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TABLE 1: Physical characteristics and muscle strength.
The training history and characteristics of the SG are presented in Table 2. For the SG, individuals were recruited who had practiced noncompetitive resistance training for hypertrophy for at least 3 years (mean, 11.77 ± 7.4 years) with no interruptions longer than 20 days and for at least 2 years before the study. Indeed, the SG subjects could back squat at least 130% of their body mass (BM) (1 repetition maximum [1RM] squat/BM = 1.86 ± 0.5) and could bench press at least 100% of their body mass (1RM bench press/BM = 1.15 ± 0.15) (5). Although the SG did not possess exactly the same volume of training, all trained with 2 to 4 training split (i.e., 2 or 3 muscle groups per day) and with the objective of hypertrophy. In the UG, subjects were sedentary for at least 2 years before the study. Criteria for exclusion were a history of renal, hepatic, cardiovascular, pituitary, or metabolic disease; use of anabolic steroids or any other medication that could affect the musculoskeletal or endocrine metabolism; smoking; adherence to a reduced-calorie or low-fat diet, ketogenic diet, or over-the-counter ergogenic aids within the past 2 months, which could affect hormonal levels (49).
TABLE 2: Training characteristics of the strength-trained group (n = 10).
Body Composition
Body mass and height were measured with an Asimed analog scale (resolution of 0.1 kg) and stadiometer (resolution of 1 mm), respectively. Body composition was assessed by using the skinfold technique. A 7-site skinfold equation was used to estimate body density (28), and percentage of body fat was subsequently calculated with the Siri equation (21). Skinfold thickness was measured from the chest, midaxillary area, subscapular area, suprailiac abdomen, triceps, and thigh.
Strength Testing
Maximal strength was assessed by using the 1RM test in the following free-weight exercises: bench press, supported barbell row, squat, and 45° leg press. Upper-body strength was considered the sum of the load lifted in the bench press and supported barbell row, and lower-body strength was considered the sum of the load lifted in the squat and leg press. Muscle strength relative to body mass was calculated, too. Before the tests, subjects were familiarized with all procedures. They warmed up for 5 minutes on a cycle ergometer, stretched all major muscle groups, and performed movements specific to the exercise tests. Each subject's maximal load was determined in a maximum of 5 trials. After each trial, the load was adjusted in accordance with coefficients specific to the number of repetitions realized (39). A 4-minute rest was allowed between trials, and the performance time for each contraction (i.e., concentric and eccentric) was 2 seconds, controlled by an electronic metronome.
Superset Strength Training Protocol
To assess the acute hormonal response to strength training, a session of training similar to that normally used for achieving muscular hypertrophy was organized. The session consisted of the performance of exercises with free weights to large muscle groups. A protocol was used with 2 supersets, each consisting of 2 exercises, and each superset was repeated 4 times to total 16 sets. Before the performance of the exercises, the individuals performed a general warm-up on an ergometric cycle and a specific warm-up for each exercise. After these warm-ups, the first superset was the agonist-antagonist type composed of the bench press and supported barbell row. The intensity of the exercises in the first superset was 75% of the 1RM, and subjects executed 8 repetitions in each set. The range of movement of both the bench press and the barbell row was from full extension to 90° of the elbow. In the second superset, squats and the leg press were performed at intensities of 75% and 65% of 1RM, with the execution of 8 and 15 repetitions, respectively. The range of movement of both the squats and the leg press were from full extension to 90° of the knee. The rest between each 2 sets ranged from 90 seconds in the first superset (i.e., bench press and barbell row) to 2 minutes in the second superset (i.e., squats and leg press). The rest between the supersets was 3 minutes. The exercises, volume, and intensity of the SSTP protocol were chosen due to the influence of the use of large muscle groups and of the hypertrophic nature of the training in stimulating anabolic and catabolic hormones (47).
Blood Collection and Analysis
Blood was obtained between 8 and 9 am, after 2 days with no training session. The time of blood collection was chosen due to its use in many studies conducted with these procedures for the control of the circadian hormonal range (1,19,27). Subjects sat in a slightly reclined position for 15 minutes before 10 mL of blood were drawn from an antecubital vein. After the collection, subjects performed the SSTP and, after 10 minutes, had another 10 mL of blood drawn with a similar technique.
After collection, the blood was maintained in ambient temperature for 45 minutes and then centrifuged for 10 minutes at 2,000 rpm, and serum was removed and frozen at -20°C for later analysis. With this blood sample, the resting and SSTP-induced concentrations of TT, FT, DHEA, and cortisol were determined in duplicate by using radioimmunoassay kits (ICN Biomedicals, Irvine, Calif.). In addition, the SHBG concentration was determined by using a chemiluminescence kit (Diagnostic Products Corp., Hawthorne, Calif.). From these values, it was possible to calculate both the TT-to-cortisol ratio and the TT-to-SHBG ratio (i.e., free androgen index [FAI]) (15). To eliminate the interassay variance, all samples were analyzed within the same assay batch, and all intra-assay variances were ≤6.3%. Antibody sensitivities were 0.02 ng·mL-1 for TT, 0.02 ng·dL-1 for FT, 0.09 ng·mL-1 for DHEA, 0.05 μg·dL-1 for cortisol, and 0.5 mmol·mL-1 for SHBG.
Statistical Analyses
The data are shown with mean and SD. The Shapiro-Wilk test was used for normality, and the Levene test was used for homogeneity. An analysis of covariance was used to adjust pretesting values to compare data among groups. Data analysis was performed with a repeated-measures analysis of variance for the comparison of the variables before and after exercise and a one-way analysis of variance for the comparison between groups. Also, the Pearson product moment correlation test was used to verify the associations between the variables analyzed. All the tests were carried out with the SPSS statistical program, version 11.0 (SPSS, Inc., Chicago, Ill.). The level of statistical significance was set at p ≤ 0.05.
Results
Resting Hormonal Concentrations
Figures 1-7 show resting hormonal concentrations. There was no difference between groups in the resting concentrations of TT, FT, DHEA, cortisol, or SHBG or in the TT-to-cortisol ratio. Although there was no difference in the TT-to-SHBG ratio between the groups at rest, the UG tended to be greater in this variable (p = 0.053). There was a significant correlation between squat strength and resting DHEA in the UG (r = 0.55; p = 0.04). Indeed, in the SG, there were significant correlations between bench press strength and the resting TT-to-SHBG ratio (r = 0.71; P = 0.02) and squat strength and the resting DHEA concentration (r = 0.65; p = 0.04).
Figure 1: Total testosterone concentrations (mean ± SD) (ng·mL-1) at rest and induced by a superset strength training protocol (SSTP). SG = strength-trained group (n = 10); UG = untrained group (n = 11). *Significantly (p < 0.05) different from resting.
Figure 2: Free testosterone concentrations (mean ± SD) (ng·dL-1) at rest and induced by a superset strength training protocol (SSTP). SG = strength-trained group (n = 10); UG = untrained group (n = 11). *Significantly (p < 0.05) different from resting.
Figure 3: Total testosterone-to-sex hormone-binding globulin ratio (mean ± SD) at rest and after a superset strength training protocol (SSTP). SG = strength-trained group (n = 10); UG = untrained group (n = 11). *Significantly (p < 0.05) different from resting. †Significantly different (p < 0.05) between groups.
Figure 4: Dehydroepiandrosterone (DHEA) concentrations (mean ± SD) (ng·mL-1) at rest and induced by a superset strength training protocol (SSTP). SG = strength-trained group (n = 10); UG = untrained group (n = 11). *Significantly (p < 0.05) different from resting.
Figure 5: Cortisol concentrations (mean ± SD) (ng·dL-1) at rest and induced by a superset strength training protocol (SSTP). SG = strength-trained group (n = 10); UG = untrained group (n = 11). *Significantly (p < 0.05) different from resting.
Figure 6: Total testosterone-to-cortisol ratio values (mean ± SD) at rest and induced by a superset strength training protocol (SSTP). SG = strength-trained group (n = 10); UG = untrained group (n = 11). There were no significant differences.
Figure 7: Sex hormone-binding globulin (SHBG) values (mean ± SD) (ng·mL-1) at rest and induced by a superset strength training protocol (SSTP). SG = strength-trained group (n = 10); UG = untrained group (n = 11). There were no significant differences.
Hormonal Response to Superset Strength Training Protocol
Figures 1-7 show the acute hormonal responses to SSTP. In the SG, there was a significant increase (p < 0.05) in response to exercise only in the serum FT level; however, postexercise changes were not observed in the concentrations of TT, DHEA, cortisol or SHBG or in the TT-to-cortisol ratio or TT-to-SHBG ratio. In the UG, there was a significant increase in response to SSTP in the serum levels of TT, FT, DHEA, and cortisol and in the TT-to-SHBG ratio (p < 0.05). There were no changes in the concentration of SHBG or the TT-to-cortisol ratio. There was no difference between groups after SSTP in the serum level of TT, FT, DHEA, or cortisol or in the TT-to-cortisol ratio. The UG had significantly higher values than the SG in the TT-to-SHBG ratio after SSTP (p < 0.05). The SG tended to have a higher SHBG concentration than the UG (i.e., 35.3 ± 17.2 ng·mL-1versus 24.3 ± 11.9 ng·mL-1; p = 0.07). There was a significant correlation between squat strength and SSTP-induced DHEA concentration in the UG (r = 0.73; p = 0.04). In addition, in the SG, there were significant correlations between bench press strength and SSTP-induced DHEA concentration (r = 0.70; p = 0.02) and TT-to-SHBG ratio (r = 0.76; p = 0.016) and between SSTP-induced DHEA concentration and leg press strength (r = 0.78; p = 0.013) and squat strength (r = 0.82; p = 0.007).
Discussion
The main findings of this study are that only the UG showed an increase in TT, DHEA, and cortisol levels and in the TT-to-SHBG ratio. Moreover, the UG demonstrated a higher TT-to-SHBG ratio than the SG after SSTP. In trained subjects, only the FT concentration increased in response to resistance exercise. For hormone concentrations at rest, no differences between groups were found in the TT, FT, DHEA, or cortisol levels or in the TT-to-cortisol and TT-to-SHBG ratios.
It was hypothesized that in the current study, long-term strength-trained middle-aged individuals would have higher concentrations of testosterone than untrained individuals would have, which was not found to be the case. Although studies evaluating young individuals have shown increases in concentrations of testosterone at rest after a period of training (1,13,33,41,48), the current findings support the longitudinal results of Häkkinen and Pakarinen (16), Nicklas et al. (43), Häkkinen et al. (18), and Izquierdo et al. (27), who showed that there was no chronic adaptation to strength training in the levels of TT or FT at rest in middle-aged individuals. In fact, changes in resting anabolic hormone levels during resistance training have been inconsistent and appear to reflect the transitory state of the behavior of these hormones and can be related to increases in the volume and intensity of training (37). Ahtiainen et al. (1) suggested that there may be a relationship between volume and intensity of training and the basal concentration of anabolic hormones. The same authors suggested that higher testosterone levels at rest are a determinant factor in the development of strength only in high-performance strength athletes. If this is the case, although the individuals in the SG had a long experience with training for muscular hypertrophy, they may not have trained at the volume and intensity characteristic of athletes, that is, sufficiently enough to produce hormonal modifications at rest. However, due to the lack of different hormonal concentrations between the groups in the current study, other physiological factors may be more directly involved in the adaptations seen with strength training. These factors may be the greater number and sensitivity of the androgenic receptors in muscle cells (6,29,50).
In the current study, the endocrine system responded in different ways to SSTP in the groups evaluated, with the trained subjects demonstrating no increases in the total testosterone, DHEA, or cortisol levels or in the TT-to-SHBG ratio. Although there is a consensus that resistance exercise is a powerful stimulant for the increase in testosterone levels (1,3,16,17,22,30,33,34), there are some discrepancies in the influence of the level of training in this respect, with some studies showing a greater response in trained individuals (2) or after a period of training (32), a greater response in individuals with a longer time in strength training (31), similar responses in trained and untrained individuals (1), and lower responses to the same stimulus after a training period (3). Furthermore, other studies have shown no significant acute increase in TT levels after exercise (43,47). It is likely that the discrepancies among all these studies are due to different strength exercise protocols or the ages or training experience of the subjects (37). Surprisingly, even with a higher absolute total load than untrained subjects (Table 1), the SG had an increased level of FT only, whereas the UG had increased levels of both FT and TT, demonstrating greater responsiveness of testosterone for the same training session. In addition, the UG demonstrated a higher TT-to-SHBG ratio than the SG after SSTP. A possible explanation may be the workout volume performed by the subjects. The trained individuals in the current study trained, on average, 11 sets per muscle group and 2 or 3 muscle groups per day; in the SSTP test, the subjects performed 16 sets. Thus, to achieve a greater testosterone response to resistance exercise, it may be necessary to perform, at least, the same stimulus that the SG subjects used to train in their daily workout. Although there may be no clear explanation for these results, a question that arises is whether the individuals in the SG might have had an adaptation to the long-term training in their endocrine system, which leads them to have an increase only in the FT level after the training session. Free testosterone is a hormone that possesses effective bioactivity at a muscular level. Total testosterone includes the testosterone linked to the SHBG, has a greater molecular weight, and therefore is incapable of traversing the capillary endothelium and integrating with regulatory elements in the nucleus (32).
Another possible explanation for the different hormone responses between trained and untrained men may be the number of androgenic receptors in the trained individuals. Many studies have demonstrated that strength training increases the number and sensitivity of androgenic receptors in muscle cells (6,25,26,29,50), and this process can be an important mechanism in adaptation to strength training (1). Thus, it is possible to speculate that the lack of a higher concentration of testosterone in the SG might have been due to a greater testosterone receptor interaction after the workout. In fact, Willoughby and Taylor (50) demonstrated a positive correlation between testosterone in an acute response and an increased number of cellular androgenic receptors (r = 0.89; p < 0.05). However, that hypothesis must be carefully researched and remains speculative.
On the other hand, it has been shown that the increase in testosterone induced by exercise may occur due to the production of lactate influencing the gonadal release (40), vasodilatory mechanisms in the testicles (42), and an increase in the sympathetic activity during exercise (10). Thus, it can be suggested that the different testosterone responses between groups could be due to adaptations in these mechanisms resulting from strength training. Some studies have demonstrated that after physical training, the production of lactate for the same relative intensity is lower (11,32,44). Other studies have demonstrated that the increase in sympathetic activity induced by exercise may be attenuated after physical training (24). Thus, although the SG performed a higher absolute workout, the relative intensity was the same in both groups, and the SSTP load could represent a stronger metabolic stressor (37,40) in the UG, probably inducing greater stimulation not only to catabolic hormones, as observed in the current study, but also to testosterone.
The increased TT-to-SHBG ratio found only in the UG and the higher values of this variable in the UG after exercise probably occurred due to the increase in the level of TT in this group. Additionally, the SG tended to have a higher concentration of SHBG than the UG (i.e., 35.3 ng·mL-1 versus 24.2 ng·mL-1; p = 0.07).
Regarding the pituitary-adrenocortical axis, many studies have shown an increase in the concentrations of DHEA and cortisol in response to the stress of training (1,30,45,47), which, in the current study, occurred only in the UG. It is possible that in the UG there was a higher metabolic stress in response to high-volume strength exercise, which caused these responses. Kraemer et al. (32) demonstrated, in younger and older subjects, lower cortisol responses to resistance exercise after 10 weeks of training. Indeed, these authors demonstrated that this adaptation is independent of adrenocorticotropic hormone (ACTH), probably due to a down-regulation in ACTH receptors. Although no differences were found in the TT-to-cortisol ratio, the levels of cortisol may impair the acute anabolic effect after the training session. Cortisol is a catabolic hormone, primarily involved in the degradation of proteins in the skeletal muscles and known to have an inhibitory effect on gonadal secretion (7,8). The current results reinforce the notion that a training session with a large volume can lead to a greater stimulus for the release of catabolic hormones for untrained individuals (47) and possibly impair the synthesis of proteins stimulated after the strength training session.
In the current study, there was a significant correlation between the levels of DHEA, before and after SSTP, and strength variables. The DHEA originating from the adrenal pathways is a precursor of testosterone that by itself in young men has no significant anabolic effect (4). Although there may not be a cause-and-effect relationship, the findings indicate a possible significance in the level of DHEA at rest and in the magnitude of the increase in this hormone after SSTP with the production of strength in middle-aged men.
To conclude, the middle-aged men in this study, whether long-term recreationally strength-trained or untrained, had different hormonal responses to a training session similar to those used to achieve muscular hypertrophy, with the trained subjects demonstrating lower responsiveness in the levels of testosterone, DHEA, and cortisol and in the TT-to-SHBG ratio. This difference could be a consequence of higher metabolic stress in response to a training session in untrained subjects. However, other mechanisms on a muscle cellular level, such as a higher androgen receptor interaction in the SG, could be responsible for the results. The lack of difference between the concentrations of testosterone at rest between the groups suggests that the recreational strength training was not capable of increasing these levels in the population studied.
Practical Applications
The results of this study are important because they offer insights into the hormonal responses of recreationally strength-trained subjects with no experimentally controlled training and could be applied to many subjects who train in gyms. Indeed, the current study indicates that the hormonal responses to strength training are different between these subjects and untrained subjects. Thus, a high volume for untrained individuals can lead to a greater stimulus for the release of catabolic hormones, and this possibility must be considered when planning strength training in untrained subjects. On the other hand, a higher volume of training may be necessary to elicit the same stimulus and produce a greater testosterone response to resistance exercise in long-term trained subjects.
Acknowledgments
We especially thank Mr. Hugo Perez and the graduate students of Dr. Francisco Lhullier for their support of this project and Ana Paula Fayh and Marcus Tartaruga for their help in the data collections. We also gratefully acknowledge all the subjects who participated in this research and made this project possible.
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