Fig. 7.1
Behavior of the most relevant hormones analyzed in relation to a 2-week intensive endurance exercise. (Reprinted from [31])
The effect of exercise volumes and intensities on male endocrine status is not well described in the literature; nevertheless, it would be important to know more precisely when the neuroendocrine system and, thus, male reproductive potential may be at risk.
The hormonal response to exercise is affected by both intensity and volume. The complexity in hormone feedback mechanisms and the disparity in results shown in the available literature demand that a consensus in study design and protocols be reached. The heterogeneity observed in different studies with regard, but not limited, to the type of athlete (sedentary vs. amateur vs. professional), the type of intervention (observational vs. modification of training or administration of exogenous hormones), etc., should be minimized.
In soccer, Grandi and Celani [86] have observed that both professional and nonprofessional players exhibit similar hormonal responses to training and to a gonadotropin-releasing hormone–thyrotropin-releasing hormone (GnRH–TRH) challenge test. Basal LH levels were higher in players during resting period than in sedentary men, but the response of LH to the challenge test was less in the players than in sedentary subjects. Although the training season did not seem to induce important hormone alterations, a strenuous soccer game induced an increase in prolactin basal levels. In basketball, it has been observed that TT increases during the season period while FT and T/C initially increase to later on start decreasing from mid-season until the end of the season [87].
Positive Effect
Most research have focused on the analysis of the acute response of the endocrine system to endurance loads, and longitudinal studies in which the long-term response to prolonged trainings is sought are sparser. Though most studies show an initial increase in levels of androgenic hormones as acute response to imposed training loads, if these are sustained in time and surpass the habitual training levels of the athletes, we could easily find with decreased basal levels of these hormones [88–91]. It is commonly accepted that the long-term effects of moderate training vary in relation to the characteristics of the used load, time of application, and the profile of the assessed athletes. Thus, it would be right to deal with the long-term effects as most likely we would find opposing results to those we find in short-term conditions [92, 93]. Frequently, we can find research concluding that middle-age subjects, or even older subjects, that perform physical activity present with testosterone basal levels that are higher than in sedentary subjects [94, 95]. However, it is necessary to understand that in order to find a response like this, it is necessary that the performed activity need not be either excessively prolonged nor it provokes great fatigue on the subject. It also has to be taken into account that the hormonal response of older subjects is not going to be as intense as in younger subjects; therefore, we may conclude that the latter have a more favorable anabolic response.
Moreover, securing a favorable hormonal response can be fulfilled with healthy life habits in which nutrition can be a key factor. In line with this, Tymchuk et al. analyzed the hormonal response to a light aerobic exercise along with a low-fat diet observing changes in the HPT axis that resulted mainly in increased SHBG [96]. Similar results have also been reported for men engaging in long-term exercise [97]. Also, in a 12-month randomized clinical study with aerobic exercise, intervention of moderate intensity in sedentary subjects resulted in increased serum DHT and SHBG [98]. In sedentary subjects submitted to low-volume exercise for 5 weeks, an increase in fT and decrease in SHBG was observed [99]. Also, when comparing sedentary subjects to physically active subjects, Vaamonde and colleagues have recently reported improved values for FSH, LH, T, and the T/C ratio. These findings further support that aerobic exercise can lead to an improved hormonal environment [58].
Resistance Training
Among the potential effects that can often be found in practitioners of resistance sports modalities (e.g., weightlifting, powerlifting, bodybuilding, and crossfit), we should distinguish those that depend on the activity itself and the intensity at which is practiced from others that are normally linked to nondesirable habits that these athletes normally follow (e.g., use of doping substances).
Use of Anabolic Androgenic Steroids
We need to bear in mind that this modality of exercise is specifically the one that we have to be careful about anabolic steroid use. Despite the fact the use of steroids significantly increases sports performance in resistance sports and provokes important increases in muscle mass of these athletes, we must not forget that the intensive and prolonged use of these substances is also linked to important androgenic effects that may derive in risks for the health of these athletes.
Although it is not the purpose of this chapter to discuss the use of anabolic steroids (for detailed information, refer to Chap. 10), due to the fact that their use is extensive among many athletes, we must note the dangerous side effects they pose for fertility and reproductive potential.
High doses of exogenous steroids alter the normal functioning of the HPT axis and inhibit the production of endogenous testosterone. The more prolonged the use of the synthetic steroid is, the more time endogenous testosterone secretion in suppressed and the longer the time for recovery to normal endogenous production may take. If the athlete wants to keep his performance level, he will enter a vicious cycle of steroid use with the risk for his own health and the possibility of being discovered and fined in an anti-doping control. When the functional situation is too adverse, it may be necessary to get the aid of a professional into trying to restore the organism’s own capacities.
Hormonal Adaptive Response to Resistance Training
Hormonal responses constitute an essential part of the mechanisms that are activated in the processes of adaptation that take place with resistance training [100–102]. Resistance exercise elicits acute postexercise hormonal responses whereas prolonged, long-term training has an effect on basal or resting concentrations [103].
An adequate anabolic–catabolic balance allows for activation of protein synthesis and increase in muscle hypertrophy, which is one of the main objectives of resistance training. Hormones such as insulin, Insulin-like Growth Factor (IGF), growth hormone (GH), and testosterone are mainly anabolic, whereas cortisol, progesterone, and myostatin are catabolic or protein-synthesis-inhibiting hormones.
The circulating levels (and ratio) of such hormones, after a resistance training session, depend on the load (volume and intensity), the used muscle mass, and the impact that the session may impose on the organism [104]. Therefore, the exercise characteristics lead to an extremely complex functional response that results in specific adaptive processes in response to the type of load used. These adaptations are based on protein metabolism which conditions the metabolism of other substances in the organism. The protein metabolites generated during sports practice along with the developed neuroendocrine response are the causes that trigger differential protein synthesis in each training type.
Negative Effect
Some research have observed an increase in the resting levels of testosterone as an adjustment to strength training in the medium- to long-term (chronic) response, [105–108]. However, when resistance training becomes excessive and the athlete comes close to overtraining or deep fatigue levels, testosterone levels may remain close to or decrease from baseline levels [109–112].
The underlying mechanisms in this type of response are not well known; however, some authors hypothesize that it may be related to functional or anatomical alterations in areas of the central nervous system as a consequence of deficit of some amino acids [26]. Other studies link this to deficits or alterations in neurotransmitters related to nervous impulse (dopaminergic, noradrenergic, or serotoninergic), or the increase in the production of testosterone-inhibiting hormones (cortisol) [113]. The person’s age may also influence the testosterone levels when trained subjects show advances in age and lowered training level [105, 112].
Positive Effect
Altering the levels of circulating anabolic hormones as well as the anabolic–catabolic ratio could be beneficial in males for several reasons. For an athlete, this can signify improving performance by increasing lean body mass and muscular strength and decreasing body fat [114]. Anabolic hormones and local autocrine/paracrine growth factors have a great effect on muscle adaptation to exercise. Since GH, IGF-I, and testosterone (T) promote muscle protein synthesis, they are directly involved in muscle adaptation. Although the effects are being described in terms of testosterone production, we have to be aware that the final result will depend on adequate interactions with the respective receptors.
Although there are some studies showing contradictory results, it is possible to assure that, generally, adequate resistance sessions provoke an increase in the testosterone levels (TT and fT) after one training session [101, 115–119].
The magnitude of changes in the levels of circulating testosterone after a resistance training session depends on different factors:
Intensity of the load which is more elevated when reaching values greater than 70 % of 1RM [102].
Volume of work, since an elevated number of repetitions for exercise, work area, and session [120] increase endogenous testosterone production. Heavy resistance training can produce an increase in testosterone, which, in turn, can have a positive effect on male fertility . The acute response of testosterone is characterized by a brief increase followed by a decline to basal, or below basal, concentrations [121, 122].
Incomplete recovery in micro and macro pauses (work:rest ratio between 0.5 and 3–5 min) [123].
Trained muscle mass (big muscle groups).
Athlete’s age. A body that is still undergoing maturation shows an endocrine behavior different from that of an adult both in resting situation and when subjected to external loading that significantly alters his equilibrium status [124].
Experience and performance level, in such way that the hormonal response is greater as years of training increase and the impact of the session elevated [111, 123, 124].
The magnitude of the load used will determine the time that testosterone levels are elevated after training [110].
Semen Alterations
Endurance Training
Negative Effect
Spermatozoa and Germ Cells
With regard to semen, studies also show controversial results regarding the effects of endurance exercise on sperm production. Nevertheless, there seems to be evidence of altered spermatogenesis and sperm output as a result of endurance training. Long-term exhaustive exercise seems to lower sperm quality and reproductive potential [35].
In runners, alterations in seminal quality have been reported by some authors, even up to 10 % of the assessed athletes exhibiting severe oligospermia [65]; conversely, other authors postulate that differences between runners and control subjects are non-existing or merely subclinical [26, 45, 61]. An increase in non-sperm cells, such as round cells, has been reported by some authors [26]; this fact would indicate possible infectious and/or inflammatory processes. Subjects with a higher training volume showed greatest differences in semen parameters [45] . Arce and colleagues [26] reported that athletes who exhibit differences in semen parameters are those with a minimum running volume of 100 km/week. Hall and coworkers reported no influence on sperm count, sperm morphology, and sperm motility after a gradually intensified training period of 6 weeks (186 % of normal training) followed by 2 weeks of detraining (50 % of normal training) [127].
Endurance-trained runners, but not resistance-trained athletes, showed altered values for sperm density, motility, morphology, and in vitro sperm penetration of standard cervical mucus [26]. Similar results have been found for high-intensity training athletes when compared to moderate-intensity ones [34]. It is worth mentioning that during recovery all parameters improved to pre-exercise levels [34].
When dealing with high-level athletes, it has to be considered that they have normally been training for many years; therefore, it becomes difficult to accurately estimate a threshold value for abnormal semen parameters. Nevertheless, a high cycling volume seems to be detrimental to sperm morphology [128]. Moreover, the same authors report that, in triathletes, a volume of 300 km/week in cycling correlates with serious fertility impairment from the sperm morphology point of view (Fig. 7.2).
Fig. 7.2
Correlation between percentage of sperm with normal morphology and cycling weekly volume (expressed as km/week)
Competition period seems to be especially deleterious for semen parameters in cyclists; in fact, cyclists have shown during this period lower sperm motility (46.2 ± 19.5 %) than either recreational marathoners and sedentary subjects (P < 0.05) or themselves at other season periods (P < 0.01) [40]. Although this study does not reveal differences in sperm morphology, it is really striking to see that it reports morphology normalcy values above 95 %. Conversely, other authors have observed lower numbers of morphologically normal sperm in long-distance competitive cyclists (41.5 for controls vs. 19.5 for cyclists) whereas no changes were observed for semen volume, motility, viability, or concentration. Moreover, they found among the observed anomalies greater proportion of tapered forms [41]. Conversely, Vaamonde et al. showed that seminological values differed significantly even in recreational athletes when they exercised to the point of exhaustion (with morphology significantly decreasing from 17 % of normal forms to 12 %, total sperm count decreasing to half the original value, and percentage of immotile sperm significantly increasing with about 10 % of subjects developing necrozoospermia) [31]. The adverse effects of exercise especially become an aggravating factor in men whose sperm parameters are already compromised due to other pathologies such as varicocele [53] .
Similar to what has been reported in endurance sports, ultraendurance athletes show significantly different values for sperm number/concentration, velocity, and morphology, as compared to physically active men or water polo players. Morphology was the parameter showing the greatest difference; this difference even reached clinical relevance for the triathletes (< 5 % normal forms) for the reference values at the time of the study [35].
In animal models with rats, it has been observed that although rats maintain their reproductive capacity after swimming stress and the offspring shows normal morphology, the number of spermatids is reduced [129]. Several studies conducted by Manna’s group [37–39], in rats as well, show a decrease in spermatogenic cells at different stages of development, such as preleptotene and midpachytene spermatocytes and stage 7 spermatids. Moreover, these authors also observed decreased levels of serum hormones, enzymes linked to hormone conversion and antioxidant agents like catalase among others. Also, in animal model, Vaamonde’s group has reported sperm morphology alterations in mice submitted to forced swimming stress; however, the same authors have observed that these alterations may be prevented with antioxidant agents like n-acetyl cysteine and, more efficiently, with trans-resveratrol [130, 131].
Oxidative Stress and DNA Fragmentation
Information regarding the effect of exercise on oxidative stress and, especially, on semen oxidative stress and DNS fragmentation is very scarce. A study has recently evidenced that in comparison to recreationally active and nonactive men, resting seminal 8-isoprostane, Reactive Oxygen Species (ROS), Malondialdehyde (MDA), and sperm DNA fragmentation are higher in elite athletes and SOD, catalase, and TAC levels are lower [43]. As expected, sperm DNA fragmentation was shown to positively correlate to VO2max, seminal 8-isoprostane, Reactive Oxygen Species (ROS), and Malondialdehyde (MDA) levels. These findings further support previous studies, suggesting that elite athletes are at greater risk of sperm dysfunction than recreational exercisers or, even, sedentary people [43]. In another work by the same group, a significant increase in seminal ROS and MDA levels and a significant decrease in seminal SOD, catalase, and total antioxidant capacity were demonstrated after 8 weeks of intensive cycling training in male road cyclists [42]. Although not in semen, it must be highlighted that there are some studies reporting a link between exercise and altered leucocyte number, especially in the case of overtrained subjects [132, 133].
Vaamonde’s group has recently reported that, similar to what happens with sperm morphology, cycling volume positively correlates with sperm DNA fragmentation. As such, athletes undergoing greater annual mean weekly training volume showed the greatest percentage of sperm DNA damage [134]. From a practical point of view, Vaamonde and colleagues have analyzed a group of ultraendurance athletes, and found high correlation between training volume and sperm DNA fragmentation, percentage of morphological abnormalities, and TUNEL(+) cells (unpublished data).
Positive Effect
Spermatozoa and Germ Cells
There is still not much scientific evidence on whether exercise or physical activity may exert a beneficial effect on seminal parameters. In fact, scientific studies in this regard are scarce. In humans, Vaamonde and colleagues [58] have recently reported improved semen parameters in physically active men (PA) when compared to sedentary people (SE). Both total progressive motility (PA: 60.94 ± 5.03; SE: 56.07 ± 4.55) and morphology (PA: 15.54 ± 1.38, SE: 14.40 ± 1.15) showed statistically significant differences. Differences in seminological parameters were further supported by hormonal differences [58]. Similar results have been reported by Palmer et al. (2012) in an animal model (C57BL6 male mice) observing improved sperm motility (1.2-fold) and morphology (1.1-fold, P < 0.05) after a swimming training protocol of 8 weeks [135]. Also in mice, running training for 14 months (from 6 months old until they were 20 months old) induced positive effect on mice testicular health. Exercising mice exhibited uninterrupted seminiferous tubules as evidenced by complete number and type of cells at the different stages of the spermatogenic cycle and also a clear lumen with great sperm density. On the contrary, sedentary mice showed a disorganized germinal epithelium and no spermatocyte-stage cells. Sertoli cells were more abundant in the runners as compared to the sedentary subjects [136].
At any rate, even if it does not entail positive effects, it seems evident that exercise does not always induce alterations in the semen profile of endurance athletes. In line with this, Lucia et al. [40] report that average values of semen parameters are usually within normal limits in endurance-trained men. Other authors defend that when these alterations are present, they are subclinical in nature [26, 27, 61, 65]. Moreover, De Souza and co-workers [27] have reported the existence of a certain “training volume-threshold” (∼ 100 km/week) for significant alterations to occur in male reproductive function . In their study, it was indeed shown that a high volume of endurance running (> 104 km/week) was associated with subclinical alterations in both the profile of sex hormones (decreased levels of total and free testosterone) and the quality of semen (particularly decreased motility and increased number of immature cells) .
Oxidative Stress and DNA Fragmentation
Exercise training seems to be able to exert modifying effects on oxidative stress , depending on the training load, training specificity, and the basal level of training. In fact, it has been reported that elite athletes have an augmented SOD capacity in comparison to recreationally active and sedentary control men [42]. The reason for this could be the greater aerobic capacity (VO2max) of the subjects with greater performance in endurance, and this parameter correlates with elevated antioxidant enzyme activity in other tissues [137].
After comparing elite athletes and recreational active men, we have observed that the least active subjects have significantly higher levels of seminal antioxidant compounds (superoxide dismutase, catalase, and total antioxidant capacity) and lower levels of seminal ROS, malondialdehyde, and 8-isoprostane, and subsequently lower rate of sperm DNA fragmentation when compared with elite athletes (P < 0.001) [43]. Significant negative correlation was observed between sperm DNA fragmentation with seminal SOD, catalase, and TAC levels (P < 0.001). Significant positive correlation was observed between sperm DNA fragmentation with seminal 8-isoprostane, ROS, and MDA levels (P < 0.001).
Also in animal models, it has been observed that, in mice, running training for 14 months (from 6 months old until they were 20 months old) reduces the levels of 8-isoprostane (marker of lipid peroxidation), nitrotyrosine, and protein carbonyl levels. Moreover, the levels of antioxidant-related enzymes such as SOD1 and GPX, among others, were increased in the runners. Therefore, lifelong running in this regard seemed to exert a positive effect [136]. Swimming exercise has also been proved beneficial to revert the pathophysiological effects of aging as changes in testosterone, and in biomarkers of inflammation and oxidative stress associated with age, were modulated by daily sessions of swimming for 15 min. The authors observed this effect in mice that started swimming early in life, at middle life, and later in life. Nevertheless, the effect was lesser when mice started exercising later in life [138]. This benefit related to age changes has also been reported by Joseph et al. in rat testes; 10-weeks of treadmill exercise induced beneficial adaptations increasing antioxidant capacity in mitochondria and decreasing DNA damage (phosphorylated histone H2AX) [139].
Even less training time (8 weeks of swimming exercise) is able to elicit a beneficial response in mice. Palmer and colleagues have observed a 1.5-fold reduction in sperm DNA damage, a 1.1-fold reduction in reactive oxygen species, and a 1.2-fold reduction in mitochondrial membrane potential [135].
As it has already been noted, exercise disrupts body homeostasis by increasing ROS and oxidative stress. As such, physically active people may suffer from ROS-induced damage that may lead to altered sperm parameters (motility, morphology, and DNA) and male subfertility. The effect is dependent on the mode, intensity, and duration of the exercise as well as the subject’s antioxidant capacity. On the other hand, it has also been noted that training may have modifying effects on oxidative stress, depending on training load, training specificity, and the basal level of training. It seems that aerobic exercise training can result in a hormetic response, giving rise to an augmented SOD activity and reduced lipid peroxidation [140, 141]. According to the hormetic hypothesis, trained and athletic people have developed, as a result of intensive training, increased total antioxidant capacity, and in particular high levels of SOD, in several tissues [142, 143]. Despite having values of antioxidants in human semen in normal and infertile men [144, 145], knowledge on the behavior of antioxidant capacity in seminal plasma as a result of training is scarce and unclear.
Though not positive effects themselves, some studies point out that sports practice does not induce negative effects on semen parameters , especially if load is not too heavy, such as the threshold established by De Souza for volume (100 km/week) [27].
Resistance Training
Negative Effect
Spermatozoa and Germ Cells
Although to date, to the best of our knowledge, there are few/none studies reporting sperm quality as a result of resistance training under physiological (nonsteroid taking) conditions, there are some reports on the effect of concomitant use of androgenic anabolic steroids along with resistance training. In this case, first, we need to be aware that many anabolic-androgenic steroids (AAS) abusers do not disclose taking AAS; moreover, they normally concurrently take antiestrogens, aromatase inhibitors, and hCG to counteract the adverse effects of AAS, such as hypogonadotropic hypogonadism and gynecomastia, and perhaps avert the detection of their use [148]. By stimulating endogenous testosterone production and preventing testicular atrophy, hCG and clomifene were until recently concurrently abused by AAS users to avoid detection of exogenous testosterone [149].
Nevertheless, supraphysiologic levels of exogenous AAS actually exert negative feedback on the HPT axis and subsequently reduce FSH, LH, and intratesticular testosterone concentration. These hormonal changes can lead to azoospermia, oligospermia, testicular atrophy, hypogonadotropic hypogonadism, and an increased percentage of morphologically abnormal sperm with amorphous spermatozoa and defects in the head and midpiece [150–152].
Usually, spermatogenesis recovers spontaneously within 4–6 months after cessation of AAS [153], although it has been reported to take up to 3 years or longer [154], maybe due to the wide variety of combinations and types of AAS. As a result of AAS abuse, there can be a transient impairment on semen quality with abnormal and hypokinetic spermatozoa [155].
It is difficult to study AAS use and its side effects because of the variable dosing as well as the prevalence of selection and information biases in research design.
In experiments performed in animal models (rats), apoptosis in the male germ line was characterized by TUNEL, caspase-3 assay, and transmission electron microscopy. The weights of the testes and accessory sex organs, as well as sperm parameters, significantly decreased in the experimental groups relative to the sham and control groups (p < or = 0.05). Germ cell apoptosis and a significant decrease in the number of germ cell layers in nandrolone decanoate exercise-treated testes were observed (p <or = 0.05). Exercise training seems to increase the extent of apoptotic changes caused by supraphysiological dose of nandrolone decanoate in rats, which, in turn, affects fertility [156].
Positive Effect
Spermatozoa and Germ Cells
The positive effect of resistance training on semen parameters has been scarcely addressed. In fact, there is no evidence that resistance training may improve semen profile; yet, Arce et al. [26] showed that sperm density, motility, morphology, and in vitro sperm penetration of standard cervical mucus were significantly altered in the endurance-trained runners, but not in the resistance-trained athletes . This seems to, at least, indicate that resistance training did not impose a detrimental effect on semen quality.
Morphofunctional Alterations of the Reproductive System
Endurance Training
Negative Effect
Testes Size and Accessory Ducts
It is difficult to examine the effect of exercise on testicular size and accessory glands and ducts in humans; however, one study on a soccer player reveals that the studied athlete exhibited testicular maldevelopment [52]. In this case, it is difficult to establish the clear cause–effect as the athlete had cryptorchidy. Nevertheless, all other symptoms worsened during periods of greater training load; therefore, it can be suspected that testicular features would also worsen during those time periods. Because of the special nature of these effects, the studies that have assessed the effect of exercise on morphofunctional characteristics of testes and accessory glands and ducts have been conducted in animal models. Manna et al. have observed the effect of different intensities of swimming exercise on testes and accessory glands and ducts, and found a decrease in testicular, epididymal, prostatic, and seminal vesicles somatic index [39].
Erectile Dysfunction, Microtrauma, and Varicocele
Erectile dysfunction (ED) or impotence has also been attributed to continuous strenuous exercise [157]. Tiredness and fatigue may reduce sexual desire and libido to the extent that it is impossible to get or sustain an erection . This phenomenon is highly associated with bicycling, as multiple studies repeatedly demonstrated the increased risk of ED in cyclists [52, 158–162] as they are more prone to suffer from microtrauma and compression due to the friction that the bike saddle imposes on the genital area. It becomes more apparent that it is not a simple fact of exercise leading to infertility , but rather that inherent parameters of exercise such as the type, volume, and intensity must also be taken into consideration and carefully analyzed.
As in the case of the studies assessing hormones, training volume was variable in the studies assessing seminal quality. Despite this inconvenience, it seems evident that subjects with a higher training volume showed greater differences. We have to bear in mind though that the reversible deleterious effects may not be reversible if athletes have been training for longer periods of time (years) or had started training around puberty.
Positive Effect
Testes Size and Accessory Ducts
Testicular atrophy is a well-known feature of the aging process; this testicular atrophy is characterized by many histological features; however, these changes seem to be dampened by exercise in animal models. As a result of a 14-month running training (from 6 months old to 20 months old), mice in the running group exhibited lower weight of both seminal vesicles and testes when compared to sedentary mice. Histological features observed in the testes of sedentary mice included areas of focal and diffused sclerosis; such findings clearly evidence tissue inflammation and degeneration [136]. Rats submitted to treadmill exercise for 10 weeks exhibited attenuated testicular atrophy, which is typical of older sedentary animals as a result of changes in mitochondria and oxidative stress profile [139].
Erectile dysfunction, Microtrauma, and Varicocele
Derby and colleagues have observed that ED may be improved by modifying unhealthy lifestyles [163]. Becoming physically active (at least 200 kcal/day) significantly improved ED condition in subjects that had been previously sedentary. So, by becoming physically active, subjects had less chance to suffer from ED than those that stayed sedentary and the chance was similar to that in subjects that were already physically active at the beginning of the study. Further studies have also observed and supported the notion that physically active subjects have less chances of suffering from ED [164, 165]. It is worth mentioning that the subjects in this study were middle-aged physically active subjects and not athletes.
Resistance Training
Negative Effect
Testes Size and Accessory Ducts
The deleterious effects of AAS , such as nandrolone decanoate, have already been mentioned. They can affect testicular ultrastructure as evidenced by transmission electron microscopy. It has been observed that these alterations include decreased number and size of Leydig cells, altered germinal epithelium (basal membrane with increased thickness and irregular wavy multilaminar appearance), and cytologic alterations (vacuoles, lipid droplets, altered mitochondria, etc.). Apoptotic features in germ were extensively observed. Though the study assessed swimming exercise, due to the fact that AAS use and abuse is common in resistance exercise, the observations have been included here. All alterations were more evident in the group of rats that were submitted to swimming exercise besides being treated with nandrolone decanoate; therefore, exercise seems to aggravate the extent of the damage induced by the steroids [166].
Mixed Modalities
There are some sports (soccer, basketball, rugby, handball, etc.) that cannot be considered as purely endurance or resistance sports, but they are to be considered as mixed modalities. From an effectiveness standpoint, these sports are based on technical actions with great dependence on strength and, therefore, anaerobic metabolism ; yet, from a competition standpoint, the sports acts have an energetic dependence on fat and carbohydrates via aerobic metabolism.
Athletes engaging in mixed modalities have also been shown to have altered values for both hormones and semen parameters . Especially, exercise seems to be an aggravating factor in the case of previous existing pathologies [52, 53]. Di Luigi’s group reported that exercise aggravated the varicocele condition of athletes. Naessen’s group reported that a soccer player’s previous existing HPG axis alteration was aggravated by physical exercise, especially as a result of increased training load, typical of competition periods. Moreover, this subject showed recurrent muscle problems and decreased libido [52]. In another study, it was observed that sperm motility was in soccer players as compared to sedentary subjects [86]. Increased C and decreased T values have been observed in rugby players during competition; conversely, these changes would revert during the post-competition period with T values increasing above basal values and C values decreasing until the fifth day post-competition [167]. It must be noted that in mixed modalities, however, it is difficult to establish clear causal and correlational relationships between volume and intensity, and even with regard to metabolic route employed as the imposed demands normally vary with regard to the type of training undertaken.
Volume-Threshold Hypothesis: True or Not?
Some of the studies have postulated the existence of a minimum volume, the so-called volume threshold, for reproductive alterations (either hormonal or seminological) to appear. The first authors in describing this were the group of De Souza [26, 27].
Afterward, although not stating a definite number of kilometers or hours of training, other authors have observed how athletes tend to show a decrease in seminal and/or hormonal parameters during competition or post-competition periods. It seems rather plausible that a threshold exists; in line with this, recent findings support this theory by showing, in triathletes, that those with the highest volume of cycling show the worst semen parameters. Interestingly enough, when assessing triathletes, Vaamonde and colleagues could observe that the athlete showing the greatest performance level of those they could analyze followed a low-volume, high-intensity training; in such a case, the semen parameters were as bad, or even worse, as those of other athletes with high training volume; moreover, this athlete exhibited low morphology, high DNA fragmentation, and TAC values in the lower end of the spectrum [44].
Even though it certainly seems a threshold exists, the wrong models have been adopted so far to prove this theory as the way it should be done would be by allocating different groups to different training volumes. However, it seems clear that intensity, as well as volume, may affect the hormonal and seminological response. Moreover, the other parameters and characteristics inherent to training (frequency, clothing, environmental temperature, possible damage to pelvic area and tendinitis, infections and/or inflammations, etc.) may also play a role. In line with this, and as in any other physiological process, the subject’s own characteristics and how his adaptive systems are prepared for the challenge will determine the final response. Those practitioners systematically undergoing high training loads presented with altered values for semen parameters . Due to the fact that exercise may produce, or aggravate previously existing, reproductive profile pathologies, such as hormonal and seminological alterations, it would be appropriate to further assess this relationship.
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