Steroids and Sports

One of the most widely discussed and controversial arenas of human performance concerns the use of steroid supplements to enhance athletic ability for a variety of sports, ranging from bicycling to baseball. There is strong evidence that human athletes have attempted to enhance their athletic performance using steroids since the 1950s, but whether, and in which sports, steroids are actually effective remains controversial (reviewed by Ryan 1981; George 2003; Hartgens and Kuipers 2004). In general, steroids used by athletes encompass a wide variety of forms of the androgen testosterone (George 2003), and most seem to have the classical androgenic and anabolic effects on men, although steroid use by women cannot be ignored (Malarkey et al. 1991; Gruber and Pope 2000). Alternative forms of testosterone (e.g., testosterone enanthate, methandrostenolone) are typically used by those desiring enhanced performance because ingested or injected testosterone is quickly metabolized into inactive forms (Wilson 1988). Therefore, the human studies we cite relate to testosterone derivatives. However, early studies on the effects of steroids on human performance had major design flaws: B. Absence of control group and double-blind study, presence of confounding factors (such as differences in training level and motivation). and inadequate statistical methods (Bhasin et al. 2001; reviewed by George 2003). Due to these issues, the question of whether and how steroids actually improve athletic performance has been debated for many years until more recent research has conclusively demonstrated the significant effects of steroids. remained unresolved.

The topic of steroid effects on human athletic performance is relevant to an emerging research area investigating the effects of hormones on performance (sprint speed, endurance, bite force, etc.) in animals (Husak et al. 2009a) because testosterone can have general effects on performance across very different vertebrate species. Our aim in this review is to interpret the effects of steroids on human performance in the broader context of hormonal action across broader taxa. We are particularly interested in learning lessons and potential research directions for animal biologists from published human studies. We conducted a selective review of studies investigating how steroid use in humans affects skeletal muscle physiology and resulting exercise performance. Although non-human performance studies have extensively addressed the impact of morphological characteristics on performance and the impact of performance on individual fitness (Arnold 1983; Garland and Losos 1994; Irschick and Garland 2001; Irschick et al. 2007, 2008. Fusaku et al. 2009a) There is relatively little general discussion of how hormones affect performance in non-human animals. We also refer the reader to several recent reviews on human steroid use and its effects for details not covered in our review (Bhasin et al. 2001; George 2003; Hartgens and Kuipers 2004).

In the vertebrate male, primary and secondary sexual characteristic development is stimulated by testosterone, and these effects may be organized or activating in nature. (Norris 1997; Hadley 2000). Organizational impacts typically occur early in development and at critical times, resulting in lasting impact. On the other hand, activating effects also occur in adults and are usually transient (Arnold and Breedlove 1985). The hypothalamus stimulates the production of gonadotropin-releasing hormone, which in turn stimulates the production of luteinizing hormone in the anterior pituitary gland. Luteinizing hormone stimulates the production of testosterone in the Leydig cells of the testicle. Testosterone then circulates throughout the body, affecting multiple target tissues that have the appropriate receptors or enzymes (such as aromatase and 5α-reductase) to convert testosterone and bind it to other receptor types ( Kicman 2008). The widespread effects of circulating testosterone levels on aggression, secondary sex characteristics, and skeletal muscle growth in males of many vertebrate species are well documented (Marler and Moore 1988; Wingfield et al. 1990; Ketterson and Nolan 1999; Sinervo et al. 2000; Ketterson et al. 2001; Oliveira 2004; Adkins-Regan 2005; In particular, testosterone production in men is associated not only with aggression, but also with the expression of color and behavioral signals (Marler and Moore 1988; Kimball and Ligon 1999; Hews and Quinn 2003; Adkins-Regan 2005; Cox et al. 2008) although the latter effect may depend on specific selective pressures on males (Cox and John-Alder 2005), increased growth (Fennell and Scanes 1992; Borski et al. 1996; Cox and John-Alder 2005).

Effects of Testosterone on Human Skeletal Muscle Physiology

Testosterone exerts multiple effects on skeletal muscle at the biochemical and cellular level, but the direct causal relationship between these effects is still unclear (Sinha -Hikim 2002; Hartgens and Kuipers 2004). ). As the studies described here and throughout the article are from experimental or correlative studies conducted in adults, the observed effects are activating in nature, leading to relatively rapid changes in phenotype. cause. Increased testosterone results in increased protein synthesis by muscle cells (Griggs et al. 1989; Kadi et al. 1999; Hartgens and Kuipers 2004), which is required for anabolic effects and increased muscle mass. Sinha Hikim et al. Eriksson et al. 2005 found that testosterone supplementation dose-dependently increased the average number of myonuclei in skeletal muscle fibers (vastis lateralis) and the number of myonuclei per fiber (Eriksson et al. 2005). This increase was also accompanied by an increase in the number of satellite cells within muscle tissue (but see Eriksson et al. 2005). Satellite cells are progenitor cells found outside myofibers that integrate into myofibers and promote muscle repair and growth (Kadi and Thornell 2000; Reimann et al. 2000). However, the mechanism by which testosterone causes an increase in the number of satellite cells is unclear, and testosterone may (1) promote satellite cell division, (2) inhibit satellite cell apoptosis, or (3) differentiate satellite cells. may be due to triggering stem cells. Inside a satellite cell (Sinha-Hikim 2002). In any case, the functional implications of these results are clear. More satellite cells likely increase the number of myonuclei per fiber, which, combined with increased protein synthesis, contributes to increased muscle fiber number and hypertrophic muscle growth (Kadi 2000; Kadi and Thornell 2000).

Testosterone also appears to cause a dose-dependent increase in muscle fiber cross-sectional area, although the details of which types of fibers are affected and where in the body this occurs remain unclear. Testosterone can simultaneously increase the cross-sectional area of ​​both type I (oxidative 'slow-twitch') and type II (glycolytic 'fast-twitch') fibers after administration (Sinha-Hikim 2002; Eriksson et al. et al. 2005), other studies, however, in doing so showed greater increases in type I fibers than in type II fibers (Hartgens et al., 1996; Kadi et al., 1999; et al., 1999). 2003), only type I fibers increase in size (Alén et al. 1984; Kuipers et al. 1991, 1993), or only type II fibers increase in size (Hartgens et al. 2002). These mixed results are interesting because they suggest that different parts of the body, and thus different performance characteristics, may be affected differently by elevated testosterone levels. A possible mechanism for these differences is changes in receptor density within the myonuclei of muscle fibers in different regions of the body (Kadi 2000; Kadi et al. 2000). An alternative hypothesis is that different fiber types have different relationships between the number of internal myonuclei and muscle cross-sectional area during exercise.

Thus, as explained above, changes in lower-level traits (protein synthesis, number of satellite cells, muscle fiber cross-sectional area) after testosterone supplementation lead to changes at the level of whole muscle, the classical It explains many of the effects. People using steroids are preferred. In other words, increased testosterone levels due to steroid use increase body weight, lean body mass, cross-sectional area, circumference, and mass of individual muscles (i.e., "body measurements"). However, a number of studies have shown conflicting results, with some or all of these properties unchanged depending on the drug used, dose, and duration of administration (Bhasin et al. 2001; Hartgens and Kuipers). reviewed by). . 2004). The finding that testosterone can alter muscle physiology and increase overall muscle size and/or body weight is consistent with results in non-human animals. For example, testosterone implants increased the size and number of auditory muscle fibers in male sea panniers (Porichthys notatus) (Brantley et al. 1993). Similarly, testosterone supplementation increased muscle mass and increased trunk muscle in male gray tree frogs (Hyla chrysoscelis) (Girgenrath and Marsh 2003) and forelimb muscles in male frogs (Xenopus laevis, Regnier, Herrera 1993; Rana pipiens, Sidor, and Blackburn). 1998).

Effects of Testosterone on Human Performance

Whether steroids actually enhance athlete performance was the subject of much debate in the 1980s and 1990s (Ryan 1981; Haupt and Rovere 1984; Cowart 1987; Wilson 1988). ; Elashoff et al. 1991; Ostrich). and Yesaris 1991. Hartgens and Kuipers 2004), largely due to flaws in the design of early studies (see above). However, in the past decade there has been a proliferation of carefully designed studies convincingly testing whether steroids improve performance, other things being equal. Hartgens and Kuipers (2004) found that 21 of the 29 studies examined showed an increase in muscle strength in humans after steroid use, with strength improvement ranging from 5 to 20%. Storer et al. (2003) found that testosterone caused dose-dependent increases in maximal voluntary leg force (i.e., weight lifted during leg press) and leg strength (i.e., rate of force generation). They further tested whether the increase in muscle strength was simply due to increased muscle mass or due to changes in the quality of testosterone-influenced muscle contraction. No change was observed in the amount of force produced. This latter finding suggests that, at least in leg press performance, testosterone enhances strength by increasing muscle mass rather than altering contractile properties. Rogerson et al. (2007) found that supraphysiological amounts of testosterone increased maximal voluntary force on the bench press (see also Giorgi et al. 1999) and increased work and power output in bicycle sprints compared to placebo controls. I discovered that Thus, 'burst' or 'sprint' performance characteristics appear to be enhanced by increased testosterone levels, which is generally consistent with studies in non-human animals (John-Alder et al. 1996, 1997; Klukowski et al. 1998; Fusak et al. 2007).

One of the problems with early studies on the effects of steroids was that participants' exercise and training histories during steroid use were not considered or controlled (Bhasin et al. 2001; George 2003; Hartgens and Kuipers 2004). ). Recent research has shown that the presence or absence of physical training during testosterone supplementation can have a significant impact on performance gains, complicating results when training is uncontrolled. Bhasin et al. (2001) reviewed several examples of such results. They found that testosterone supplementation alone was able to improve strength from baseline, but training alone with placebo also produced strength gains, and that training-only strength levels were comparable to testosterone supplementation alone. (Bhasin et al.1996). Testosterone supplementation during exercise usually produces the greatest increases in muscle strength compared to pure exercise or testosterone alone (Bhasin et al. 1996, 2001). These results are consistent with others (reviewed by George 2003). Indeed, George (2003) suggested that steroids will only consistently enhance strength if three conditions are met: (1) steroids are given to individuals who have been training and who continue to train while taking steroids, (2) the experimental subjects have a high protein diet throughout the experiment, and (3) changes in performance are measured by the technique with which the individuals were training while taking steroids. That is, one may, or may not, find a change in bench-press performance if individuals trained with leg presses, and not bench presses, while taking steroids. We note that the confounding effect of training is a rather intuitive finding, but it does point out potential problems in studies of non-human animals, specifically laboratory studies, which we address below.

Implications of studies of humans for studies of nonhuman animals

Given the effects of steroids on physiology and performance of human muscle, what can integrative biologists take away from these findings? We suggest that they can provide some valuable insights into the mechanisms of how hormones might regulate whole-animal performance traits in nonhuman animals. The most obvious lesson is that manipulating circulating levels of testosterone or its derivatives improves overall strength, which apparently has a positive effect on shock wave performance such as sprint speed. In contrast, there is little evidence from human studies for beneficial effects on endurance, which is counterintuitive given testosterone's known effects on hemoglobin concentration and hematocrit. But these same studies in humans also raise many questions that deserve close attention for researchers interested in hormone effects in non-human animals, such as the effects of exercise, timing of administration, and dosage. I am filing. We also argue that more information is needed about the long-term effects of hormonal manipulation on performance and fitness. Although recent research suggests that increased testosterone levels may improve certain types of performance, we do not endorse or justify the use of steroids in humans. . Long-term steroid use in humans has numerous side effects, including cardiovascular disease, reproductive dysfunction, behavioral changes, and increased risk of certain medical conditions.

Despite popular interest in steroids and their effects on human athletic performance, we still lack a broad understanding of the effects of testosterone on performance in different animal species.

Our review of the literature on human steroids highlights several issues that could prove useful for integrative biologists interested in determining links among hormones, morphology, performance, and fitness in nonhuman animal species. First, studies of steroid use by humans reveal many caveats related to experimental design and interpretation that should be considered by those studying nonhuman animals (e.g., training, diet, dosage effects). Second, because of conflicting results of testosterone on different performance traits (e.g., burst performance versus endurance), more data are needed for such biomechanically opposing performance traits; testosterone may enhance multiple kinds of performance in some species, and only one kind in another. Third, while testosterone may have some general effects on dynamic performance in vertebrates, are there other hormones (e.g., juvenile hormone) that play a similar role in invertebrates? Finally, people who abuse steroids often use a variety of "stacking" systems in which they take multiple drugs in a specific order (George 2003), and those who use them are more likely to believe that such treatment is effective. I believe it will greatly improve dynamic performance. However, it is not clear how these regimens affect performance, or how different regimens are more or less effective in enhancing performance in both human and non-human animal species. Few studies have investigated Moreover, such practices are not limited to multiple androgens, but may include other hormones, such as growth hormone and insulin-like growth factor I, which, when exogenously ingested, may alter athletic performance and phenotypic changes. aspects may also improve (Gibney et al. 2007)). As such, the interacting effects of different hormonal therapies for improving animal performance are poorly understood. In summary, we advocate an integrative approach to study the evolution of morphology, function, and the endocrine system, and to strengthen collaboration among researchers interested in human and other animal systems. may prove beneficial for both groups.