How the Debate Over Men in Women’s Sports Both Obscured and Advanced Sport Science

A cautionary tale about policy, science, and the cost of abandoning clear definitions.

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About the Author

Dr. Greg Brown is a professor of Exercise Science at the University of Nebraska at Kearney. He teaches courses in Exercise Physiology, Exercise for Special Population, and Professional Development in Exercise Science. He has also taught Anatomy & Physiology, Sports Nutrition, Research Methods, Education Research, and more. His research focuses on the effects of nutritional supplements, physiological responses to exercise, and sex differences in sports performance. He has over 60 peer-reviewed publications and serves as a peer reviewer for numerous academic journals. Brown is an active member of several professional organizations, including the American College of Sports Medicine and the National Strength and Conditioning Association. He enjoys running, hunting, fishing, and spending time with his family. He and his wife, Amber, have two sons, one daughter in law, and a grandson.

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The inclusion of males who identify as girls or women—often called transgirls or transwomen—in the female sports category has had profound and damaging consequences for girls’ and women’s athletics. Female athletes have been injured and deprived of roster spots, starting positions, awards, and championships in their own category, all due to the mistaken belief that a transgender identity somehow negates the well-documented performance advantages conferred by male sex.

Beyond these direct harms, the politicization of transgender inclusion has also distorted the field of sport science itself. High-profile journals have published opinion pieces and low-quality studies that downplay or deny sex-based performance differences, which are then amplified by credulous media coverage under headlines like “Separating Sports by Sex Doesn’t Make Sense.” Ironically, however, this controversy has also forced sport science to revisit foundational questions about sex-based differences in anatomy and physiology and the resulting differences in athletic performance, which may ultimately benefit female athletes in the long run.

This is not to suggest that the harms imposed on female athletes were either necessary or justified. Rather, it underscores that any renewed scientific attention to female performance has emerged as an incidental byproduct of policy failure, not as a vindication of it.

Two books published in recent years provide essential context for understanding how the debate over transwomen in women’s sports evolved from fringe speculation to settled international policy, and then to a central flashpoint in contemporary politics. In Unsporting: How Trans Activism and Science Denial are Destroying Sport, coach Linda Blade, PhD, traces the origin of transgender inclusion policies to ideological shifts within sport governance and the systematic sidelining of biological science. Similarly, in Unfair Play: The Battle for Women’s Sport, Lady Sharron Davies, MBE, documents how what was once an unthinkable proposition—allowing males to compete in the female category—became official International Olympic Committee policy in 2015 and a major political controversy soon thereafter. Taken together, these works offer a clear account of not only what has happened, but how it happened, and why science has been both deployed and distorted along the way.

Dithering Over Details: From Definitions to Thresholds

For most of history, the terms “man” and “woman,” “boy” and “girl” had clear and universally understood meanings. Men were adult human males; women were adult human females, and so on. Even as the concept of gender roles began receiving scholarly attention in the mid-20th century, with debates emerging about “men’s work,” “women’s work,” and sex-based stereotypes, there was no serious confusion about the existence or importance of biological differences between males and females. In sport, this clarity translated into straightforward policy: males competed in boys’ and men’s categories, and females in girls’ and women’s.

That clarity began to erode in the late 20th and early 21st centuries, as transgender activism pushed to redefine “man” and “woman” around one’s self-identified “gender identity” rather than biological sex. What followed was a cascade of sporting policies that treated sex as negotiable and biology as incidental. The result was a patchwork of rules: some required males to undergo genital surgery and clinical treatment for what was then termed “transsexualism” before entering women’s competition; others mandated suppression of testosterone regardless of retained male anatomy or puberty-driven advantages; still others dispensed with medical requirements altogether, asserting that identifying as a girl or woman was sufficient. Each approach rested on arbitrary judgments about whether male athletic advantages could be erased through medical intervention, or even whether such advantages existed at all.

Once sex was treated as a modifiable variable rather than a defining category, sport science was asked to solve a problem it was never designed to address. Laboratory and field tests can, of course, measure changes in strength, endurance, or speed following testosterone suppression in males. But such metrics cannot capture the full range of sex-based differences that shape athletic performance. Lowering circulating testosterone does not undo the structural, developmental, and physiological advantages conferred by male sex, nor do isolated laboratory outcomes translate neatly into fairness on the field of play.

Determining how much so-called “gender-affirming therapy” (GAT) impairs male athletic performance in order to justify inclusion in the female category is fundamentally at odds with the purpose of sport science. The discipline exists to understand the biological determinants of performance and to identify how training, nutrition, and recovery can maximize athletic capacity—not to engineer performance decreases to satisfy eligibility rules. Treating impairment as a scientific objective inverts the discipline’s core mission and highlights the category error at the heart of these policy debates.

Consider two separate research projects examining annual physical-fitness test results among male U.S. Air Force personnel who underwent testosterone suppression as part of GAT. In both studies, males substantially outperformed their female peers before intervention, completing more push-ups and sit-ups and running 1.5 miles considerably faster—clear evidence of male advantages in strength, endurance, and speed. Both studies also reported reductions in physical-fitness scores after one to four years of hormonal intervention. Yet taken as a whole, the findings fail to provide a clear or reliable estimate of how much testosterone suppression actually reduced athletic performance. Neither study adequately accounted for changes in physical activity, body composition, nutrition, motivation, or other variables known to influence performance, making it impossible to isolate testosterone suppression as the causal mechanism.

More importantly, even perfectly controlled measurements of average performance declines would still miss the central point. Eligibility for a protected sports category has never turned on whether an athlete’s advantage has been sufficiently reduced, but on whether the athlete belongs to the category at all. Participation in age-based divisions, for example, does not depend on meeting a performance threshold; it depends on the objective fact of age. Because the physical differences associated with maturation are obvious and well documented, no one proposes or funds research to determine whether unusually strong high-school students should be allowed to compete in middle-school sports based on their self-perceived immaturity. Nor does anyone commission research to assess whether heavyweight athletes should be eligible for lighter weight classes based on their self-perception of body weight.

Yet in stark contrast to these settled principles, the International Olympic Committee funded research to evaluate whether testosterone suppression could sufficiently reduce male athletic advantages to permit fair competition in the female category. The stated goal was to resolve whether males could compete fairly in female category. That research—most notably a cross-sectional comparison of highly fit female athletes with relatively unfit males—was so fundamentally flawed in both design and analysis that it failed to provide any reliable estimate of how much sport-relevant performance is reduced by testosterone suppression. More critically, it failed to answer the very question it was ostensibly commissioned to resolve: whether fairness in female sport can be preserved if males are allowed to compete in the female category.

As this research failed to deliver clarity, policymakers and sport scientists became mired in increasingly pedantic debates over testosterone thresholds. Would suppressing testosterone below 10 nmol/L suffice? What about 5 nmol/L—or 2.5? If a numerical cutoff were to determine eligibility, further questions inevitably followed. How long must testosterone be suppressed—one year, two years, three? And by what means would compliance be verified? Still more debates centered on whether, and how, one might quantify a sufficient reduction in male athletic performance to justify entry into women’s competition. Given well-documented sex-based performance gaps—roughly 10–15 percent in running speed, 25–50 percent in aerobic capacity, and 30–60 percent in muscular strength—would a male need to demonstrate a comparable reduction in only one domain? Or in all of them simultaneously?

These questions were debated endlessly in legislative hearings, sport governing body committees, and scientific forums. Yet all of this dithering over details missed the fundamental point. The female sports category was never created to accommodate males who could reduce their athletic advantages enough to qualify. It was created to provide a protected competitive space for females, whose athletic performance differs categorically from that of males by virtue of sex-based biology.

This entire framework of justification has been criticized as a form of moral asymmetry rooted in misogyny. Female athletes are expected to sacrifice fairness, safety, and opportunity in the name of inclusion, while no parallel expectation is placed on males to accommodate gender nonconformity within their own teams, locker rooms, or competitive categories. The burden of inclusion, in other words, falls almost entirely on females, even though they are the very group for whom sex-segregated sport was originally created.

From Calibration to Clarity

The good news is that this controversy has begun to produce increased protections for the female sporting category. In 2021, World Rugby announced that athletes who have experienced male puberty would no longer be eligible to compete in women’s rugby, citing concerns about both safety and fairness. Other international sport governing bodies—including World Athletics, World Aquatics, and the Union Cycliste Internationale—have since adopted similar sex-based eligibility rules for female competition.

In the United States, more than two dozen states have enacted laws prohibiting males from competing in girls’ and women’s state-sponsored school sports. At the federal level, a Presidential Executive Order and subsequent policy responses prompted organizations such as the National Collegiate Athletic Association and the U.S. Olympic and Paralympic Committee to substantially narrow the circumstances under which males may compete in the female category. In the United Kingdom, following a Supreme Court decision affirming that the terms “woman” and “girl” refer to females defined by biological sex, numerous sport governing bodies have likewise moved to reinforce sex-based eligibility criteria in women’s sport.

This shift toward definitional clarity is occurring alongside renewed legal scrutiny. On January 13, 2026, the U.S. Supreme Court will hear oral arguments in Hecox v. Little and B.P.J. v. West Virginia, cases that directly address whether states may preserve sex-based categories in girls’ and women’s sports in light of well-established biological differences between males and females.

Within sport science itself, there has also been a renewed and more deliberate reexamination of sex-based differences in athletic performance. In 2023, the American College of Sports Medicine published a consensus statement reaffirming the well-established performance gaps between adult males and females, as well as the biological factors underlying those differences. While the statement downplayed sex-based performance differences prior to puberty—largely reflecting a historical lack of focused research in that area—recent research have begun to fill that evidentiary gap. Over the past two years, multiple peer-reviewed studies using competitive performance data have reported statistically significant prepubertal sex differences across sports, consistently showing that boys run and swim faster and throw and jump farther than girls.

Ultimately, the debate over transwomen’s inclusion in female sports has revealed far more about institutional hesitation than about scientific uncertainty. The relevant biological differences between males and females were never obscure, nor was the purpose of the female sporting category ambiguous. What obscured clarity was the attempt to enlist sport science in service of a predetermined policy outcome, rather than to describe reality and define categories accordingly. When sport science was pressed into service to calibrate “fairness” instead of explaining sex-based performance differences, it became mired in ever finer details that could never resolve a categorical problem.

Recent policy reversals and renewed scientific attention suggest a return to first principles. Clarity emerges when definitions are restored and evidence is permitted to speak plainly. The lesson is not that sport science failed, but that it is most valuable when it resists ideological pressure and remains anchored to biological reality. Protecting the integrity of female sport requires nothing more and nothing less.

In the end, sex was never the problem. The failure to defend its importance was.

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