Groundbreaking study finds no evidence that trans athletes are ‘a threat’ to women’s sports

The inclusion of transgender women in women’s sports has become a battleground in a larger culture war. Positions are often based on ideological or moral convictions. However, a medical and scientific debate also underlies this issue — a debate that is now closer to being resolved. A scientific team from Brazil has conducted a meta-analysis encompassing 52 studies and 6,485 participants, analyzing the body composition and physical fitness of transgender and cisgender women. While transgender women showed greater lean mass — indicating greater muscle mass — they did not exhibit greater physical capacity, such as strength or aerobic fitness, than cisgender women.

“This refutes the logic behind blanket bans on transgender women in sports,” argues Bruno Gualano, a physician and researcher at the University of São Paulo in Brazil, who co-authored the study. “Most of these policies are based on the assumption that transgender women retain inherent physical advantages and would therefore dominate women’s competitions. The data does not support this idea.”

The meta-analysis, published in the British Journal of Sports Medicine, analyzed 2,943 transgender women who had undergone hormone therapy for one to three years. It found no evidence of any physical advantage. There were no observable differences in upper or lower body strength, or in maximum oxygen consumption — a key measure of cardiorespiratory fitness — between trans and cisgender women. In fact, after gender-affirming hormone therapy, transgender and cisgender women showed similar levels of physical fitness across all variables analyzed. Therefore, based on the scientific evidence, Gualano concludes that transgender women “do not pose a threat to women’s sports.”

“The research, which can be considered high quality, introduces doubts where, apparently, none existed before,” notes Carlos Alberto Cordente Martínez, professor of physical activity and sports sciences at the Polytechnic University of Madrid. “At the very least, this should lead us to reconsider certain maximalist positions in the field of competitive sports,” he reflects in statements to the scientific portal SMC Spain.

This isn’t the first retrospective study on the topic. A recent Spanish team analyzed 14 medical articles on transgender women and competitive sports. “We concluded that more than two years of post-pubertal hormone therapy are necessary to achieve a significant reduction in the effects of male hormones on various physiological parameters,” explains María Miguélez González, an endocrinologist at the Gender Unit of the Gregorio Marañón Hospital and co-author of the study. At that time, it was recommended that the research be expanded with longer-term studies.

This is the same conclusion reached by Miguélez after reading the new meta-analysis. “The studies are short in duration, less than three years,” she points out. Furthermore, the expert notes other limitations: “Only nine of the 52 studies analyzed were clinical trials, which are the ones that provide the highest quality scientific evidence.” And finally, she points to “the lack of data on elite athletes.”

The 52 studies on which this analysis is based have different designs and methodologies, Gualano acknowledges. The body of scientific evidence, therefore, is not entirely conclusive and is of heterogeneous quality. “It’s not perfect, but it’s the best scientific evidence available,” he argues. Regarding the absence of trans women in elite sports, Gualano is emphatic: “That gap exists because, to begin with, there are hardly any trans women competing.”

Only one transgender woman has ever participated in the Olympic Games: Laurel Hubbard at Tokyo in 2020. In the weightlifting competition, she failed all three of her snatch attempts and did not win a medal. After the Olympic Games, following an intense campaign of harassment, she announced her retirement from the sport. She is likely the first and last transgender athlete to participate.

The International Olympic Committee has announced its intention to reinstate genetic testing, which was abandoned more than 30 years ago, to bar transgender women from the Olympic Games. Until now, it had followed an open policy that allowed individual federations to set their own rules, and the most widely accepted standard was a threshold of natural testosterone, the male hormone: anyone who exceeded it was excluded

The reality is that, although transgender men and women participate in sports, very few do so at an organized level. Charlie Baker, president of the NCAA, the main organization that regulates and organizes college sports in the United States, said in an interview that fewer than 10 transgender athletes were competing under his governing body, which encompasses more than half a million people. He made this statement after the Trump administration issued an executive order called “Keeping Men Out of Women’s Sports” — one of the first policy decisions of his second term.

Bea Sever, spokesperson for the Association of Families of Transgender Minors of Navarre and the Basque Country, stated in an interview with the Cadena SER radio network that, although nearly 70% of transgender people participate in sports, only 6% do so in organized groups, because they perceive it as an unsafe environment. Their presence is not just a minority, it’s negligible: 0.01% (6% of transgender people participate in sports, and they represent around 0.3% of the population).

In the debate over the participation of trans people in federated and professional sports, there is always one group that is ignored, pushed out of the spotlight: trans men. The new study also analyzed their strength and body composition to assess possible biological advantages or disadvantages. Trans men were found to have less lean mass than cis men and less upper‑body strength. In those two variables, they surpassed cis women. The rest of the variables could not be compared due to the lack of data.

The present study is inconclusive. Further research is recommended, but with the available data, it cannot be said that trans women have a biological advantage over cisgender women. The medical‑scientific debate appears to lean toward allowing this group to participate, but the political and ideological debate is far from over.

There’s even a philosophical dimension to the debate. “Philosophically speaking, I agree that facts alone don’t tell us what we should do,” Gualano reflects. “It’s the classic ‘is-ought’ problem that Hume pointed out.” The Scottish philosopher David Hume observed that many philosophers and moralists jump from describing how things are to saying how they ought to be without justifying that leap. No prior moral premise is added. In this debate, the fact that trans people have been excluded from sports for centuries does not mean they should continue to be excluded. That it has been so does not justify that it should remain so.

In any case, if a minority group is to be excluded or penalized based on a biological argument, the very least that should be required is that the argument be well-founded. “Good scientific evidence doesn’t dictate values, but it could guide how we apply them,” Gualano reflects. “That’s the role this article aims to play.” For this reason, the expert calls for analyzing the debate within a broader context, taking into account the exclusion and violence faced by the trans community. “We believe the debate should be guided by values ​​fundamental to sport itself, such as fairness, inclusion, and human dignity, rather than sweeping bans,” he concludes.

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