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Do anabolic steroids make you a better athlete? - Scientific American
Irschick; Steroid use and human performance: While recent studies have begun to address how hormones mediate whole-animal performance traits, the field conspicuously lags behind research conducted on humans. Recent studies of human steroid use have revealed that steroid use increases muscle cross-sectional area and mass, largely due to increases in protein synthesis, and muscle fiber hypertrophy attributable to an increased number of satellite cells and myonuclei per unit area.
These biochemical and cellular effects on skeletal muscle morphology translate into increased power and work during weight-lifting and enhanced performance in burst, sprinting activities. However, there are no unequivocal data that human steroid use enhances endurance performance or muscle fatigability or recovery. The effects of steroids on human morphology and performance are in general consistent with results found for nonhuman animals, though there are notable discrepancies.
However, some of the discrepancies may be due to a paucity of comparative data on how testosterone affects muscle physiology and subsequent performance across different regions of the body and across vertebrate taxa. Therefore, we advocate more research on the basic relationships among hormones, morphology, and performance.
Based on results from human studies, we recommend that integrative biologists interested in studying hormone regulation of performance should take into account training, timing of administration, and dosage administered when designing experiments or field studies. We also argue that more information is needed on the long-term effects of hormone manipulation on performance and fitness. 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 s, but whether, and in which sports, steroids are actually effective remains controversial reviewed by Ryan ; George ; Hartgens and Kuipers In general, steroids used by athletes encompass a wide variety of forms of the androgen testosterone George , and most seem to have the classical androgenic and anabolic effects on men, although steroid use by women cannot be ignored Malarkey et al.
Alternative forms of testosterone e. Thus, studies of humans that we cite involve testosterone derivatives. Early studies of the effects of steroids on human performance, however, had major flaws in design, such as lack of control groups and a double-blind procedure, the presence of confounding factors e. These problems left open for many years the question of whether, and in what capacity, steroids actually enhance athletic performance, until more recent studies conclusively showed significant effects of steroids.
Our goal in this review is to interpret the effects of steroids on human performance in this broader context of hormonal effects across a wider range of taxa. We are particularly interested in drawing lessons and potential avenues of research for animal biologists from published research on humans. We have performed a selective review of studies examining how humans' use of steroids affects skeletal muscle physiology and subsequent athletic performance.
While studies of performance on nonhumans have dealt extensively with the effects of morphological traits on performance and the impact of performance on individual fitness Arnold ; Garland and Losos ; Irschick and Garland ; Irschick et al. We also point the reader towards several recent reviews of steroid use and performance by humans for details not discussed in our review Bhasin et al. The development of primary and secondary sexual characteristics is stimulated by testosterone in vertebrate males, and these effects can be either organizational or activational in nature Norris ; Hadley Organizational effects tend to occur early in development, and during a critical window of time, thereby resulting in permanent effects.
On the other hand, activational effects occur in adults, and the effects are typically temporary Arnold and Breedlove The hypothalamus stimulates production of gonadotropin-releasing hormone, which in turn stimulates production of luetenizing hormone in the anterior pituitary. Luetenizing hormone then stimulates production of testosterone in the Leydig cells of the testes.
Testosterone then circulates throughout the body where it exerts effects on multiple target tissues that have the appropriate receptors or appropriate enzymes e. The widespread effects of circulating levels of testosterone on aggression, secondary sexual traits, and growth of skeletal muscle in males of many vertebrate species are well-documented Marler and Moore ; Wingfield et al.
In particular, production of testosterone by males has been linked with the expression of color and behavioral display signals, as well as aggression Marler and Moore ; Kimball and Ligon ; Hews and Quinn ; Adkins-Regan ; Cox et al. Testosterone has multiple effects on skeletal muscle at the biochemical and cellular levels, but the direct cause-and-effect relationships among these effects are still unclear Sinha-Hikim ; Hartgens and Kuipers The studies that we discuss here, and throughout the paper are from experiments or correlative studies conducted on adult individuals such that the effects seen are activational in nature, causing rather rapid changes to the phenotype.
Increased testosterone causes increased protein synthesis by muscle cells Griggs et al. This increase was also associated with an increase in the number of satellite cells in the muscle tissue but see Eriksson et al.
Satellite cells are progenitor cells found external to muscle fibers that are incorporated into fibers and promote repair and growth of the muscle Kadi and Thornell ; Reimann et al. However, the mechanism by which testosterone causes an increase in the number of satellite cells is unknown and could be due to testosterone 1 promoting cell division of satellite cells, 2 inhibiting apoptosis of satellite cells, or 3 causing differentiation of stem cells into satellite cells Sinha-Hikim In any case, the functional implications for these findings are clear.
More satellite cells likely result in more myonuclei per fiber, which, combined with increased protein synthesis, contribute to increases in muscle growth via an increased number and hypertrophy of muscle fibers Kadi ; Kadi and Thornell Testosterone also appears to cause a dose-dependent increase in the cross-sectional area of muscle fibers, although details about which types of fibers are affected and where in the body this occurs remains equivocal. These mixed results are intriguing, because they suggest that different parts of the body, and, hence, different performance traits, may be affected differently by elevated testosterone levels.
The likely mechanism for these differences is variation in density of receptors within the myonuclei of muscle fibers in different regions of the body Kadi ; Kadi et al.
An alternative hypothesis is that different types of fiber have differing relationships between the number of internal myonuclei and muscle cross-sectional area during hypertrophy Bruusgaard et al. If either of these hypothesized mechanisms is correct, then circulating levels of testosterone may only explain a portion of inter-individual or interspecific variation in performance.
Testosterone may also stimulate changes in the proportions of types of fibers in muscles Holmang et al. For example, Sinha-Hikim et al.
Changes in lower-level traits e. That is, increasing testosterone via steroid use increases body weight, lean body mass, as well as cross-sectional area, circumference, and mass of individual muscles i. For example, testosterone implants increased size and number of fibers in the sonic muscles of male plainfin midshipman fish Porichthys notatus Brantley et al.
Similarly, testosterone supplementation increased muscle mass and changed contractile properties of trunk muscles of male grey treefrogs Hyla chrysoscelis Girgenrath and Marsh and of forelimb muscles of male frogs Xenopus laevis , Regnier and Herrera ; Rana pipiens , Sidor and Blackburn Whether steroids actually enhance performance of athletes was a subject of great controversy throughout the s and s Ryan ; Haupt and Rovere ; Cowart ; Wilson ; Elashoff et al.
However, the past decade has seen a surge in more carefully designed studies that have convincingly tested whether, all else equal, steroids increase performance. They further tested whether increased muscle strength was due simply to increased muscle mass or to changes in the contractile quality of muscle affected by testosterone, but they found no change in specific tension, or in the amount of force generated per unit volume of muscle.
This latter result suggests that, at least for leg-press performance, testosterone increases strength by increasing muscle mass and not by changing contractile properties. For example, experimentally elevated levels of testosterone caused increased sprint speed, relative to sham-implanted individuals, in northern fence lizards Sceloporus undulatus Klukowski et al.
These findings contrast with results for endurance events, in which no increase in performance has been detected experimentally in humans reviewed in George ; Hartgens and Kuipers More studies of the effects of increased testosterone on endurance would help to better clarify these seemingly paradoxical findings.
Steroid use does not seem to consistently enhance recovery time after strenuous exercise reviewed in Hartgens and Kuipers , although it may in non-human animals Tamaki et al. Recent studies have shown that the presence or absence of exercise training during testosterone supplementation can have a marked impact on how much performance is enhanced, thus complicating results when training is not controlled.
They pointed out that testosterone supplementation alone may increase strength from baseline levels, but so will exercise alone with a placebo, such that strength levels with exercise alone are comparable to those with testosterone addition alone Bhasin et al.
Testosterone supplementation while undergoing exercise training typically has the greatest increase in strength compared to exercise only or testosterone only Bhasin et al. These findings are consistent with those of others reviewed by George Indeed, George suggested that steroids will only consistently enhance strength if three conditions are met: 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. 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 the circulating levels of testosterone, or its derivatives, increases overall strength, which has apparent benefits for performance in bursts, such as sprint speed. In contrast, there is little evidence from studies on humans for a positive effect on capacity for endurance, which is counter-intuitive, given the known effect of testosterone on hemoglobin concentrations and hematocrit. However, these same studies of humans also raise a host of issues that merit special consideration by researchers interested in hormonal effects on nonhuman animals, including effect of training, timing of administration, and dosage administered.
We also argue that more information is needed on the long-term effects of hormonal manipulation on performance and fitness. Although recent studies suggest that increasing testosterone levels can enhance certain types of performance, we are not advocating or justifying the use of steroids by humans. We encourage researchers to complete more detailed studies of the interactions among hormones, morphology, and performance, especially across different types of performance traits dynamic versus regulatory, see Husak et al.
Comparative data on whether the same, or different, hormones affect the same performance traits in different taxa e. A comparative approach is important, as other studies have shown different effects of testosterone on performance in different taxa e. Even though testosterone is confined to vertebrates, it is possible that studies with invertebrates may reveal similar effects on performance via different hormones, e. Correlative studies relating endogenous circulating hormone levels to natural variation in performance traits can provide valuable insight into potential mechanistic regulators of performance, but manipulations allow a more detailed examination of cause-and-effect relationships.
Whether performance can be manipulated by reduction castration or supplementation implants of testosterone in nonhuman animals will depend on the type of performance and how it is affected by circulating levels of the androgen. For example, supplementation with testosterone may rapidly increase display behavior or aggression in the laboratory Lovern et al. These examples are in contrast to supplementing testosterone in the laboratory and testing for an effect on performance.
Aggression and coloration will not likely require training of the target trait to reveal an observed effect, whereas some performance traits may require training. Furthermore, regulatory performance traits e. It is also important to more closely inspect those traits that show no significant effect of testosterone on dynamic performance after manipulation in the laboratory.
However, a second possibility is that muscles involved in performance were not adequately trained during administration of supplemental testosterone, or there was no control of exercise during the period of testosterone administration. As an hypothetical example, one might not expect to see a large increase in the maximal flight speed of birds that were never allowed to fly following administration of exogenous testosterone.
Indeed, Gallotia galloti lizards given exogenous testosterone were compared to lizards given sham implants and there was no difference in maximal bite force at the end of the experiment K. Herrel, in review , despite increases in mass of the jaw muscles in testosterone-supplemented males. It is also possible that receptor density is very low or becomes low in trained muscles. Nevertheless, while training in animals seems straightforward in principle, in practice it is far trickier, and there also appear to be striking differences among species in the effects of training.
Whereas some studies of mammals have successfully increased performance through training in a laboratory Brooks and Fahey ; Astrand and Rodahl , similar studies with lizards have found no effect Gleeson ; Garland et al. In addition, while training might be successful with animals acclimated to a laboratory setting, inducement of stress, with a concomitant effect on corticosterone Moore and Jessop , and potentially circulating testosterone levels, is a significant confounding factor.
Consequently, this approach could result in unpredictable results in how hormones impact performance, unless one accepts the unlikely assumption that all experimental animals are performing in the same ways. Studies seeking to manipulate performance with testosterone supplementation should also consider the timing of experiments.
For example, testosterone should ideally be increased or decreased during times when the hypothalamic—pituitary—gonad HPG axis is responsive and receptors are expressed in the appropriate target tissues. Seasonal sensitivity of the male HPG axis is well documented Fusani et al. For example, male green anoles Anolis carolinensis given exogenous testosterone after the end of the breeding season in a laboratory setting did not increase head size or bite-force performance J.
Moore, unpublished data , presumably because some or all of the relevant target tissues were no longer sensitive to androgens. On the other hand, male brown anoles Anolis sagrei did show enhanced maximal bite force when testosterone was supplemented at the beginning of the breeding season when the target tissues are presumably sensitive to androgens Cox et al.
Timing of experimentation is thus critical for designing studies examining hormonal effects, and the interaction between timing and training should also be considered, as training effects may be relevant for some seasonal periods, but not for others.
A related issue concerns how much hormone to administer to experimental subjects.