New Research Challenges Assumptions: Trans Women Have No Fitness Advantage Over Cis Women

The fierce debate over fairness in women’s sports is almost entirely driven by the conviction that biological male puberty creates a permanent athletic edge. This belief has shaped global policies and fueled intense arguments, often resting on the idea that certain physical advantages are impossible to reverse.

Yet, emerging research is beginning to challenge this narrative with hard data rather than assumptions. As scientists look closer at the actual effects of hormone therapy on strength and stamina, the findings suggest that the playing field may be far more level than many previously believed.

Is There Really an Unfair Advantage?

The debate around transgender women in sports often centers on a single, powerful concern: fairness. Critics argue that biological differences give trans women an insurmountable edge, making competition uneven from the start. However, a major new analysis suggests that this long-held assumption does not hold up against scientific scrutiny.

Published in the British Journal of Sports Medicine, a research team from the University of São Paulo reviewed 52 separate studies involving over 6,000 participants. This comprehensive review included data from nearly 3,000 transgender women who had been on hormone therapy for at least one year. The goal was to move past political opinions and look at hard data regarding body composition and physical ability.

The results offer a different perspective than what is often heard in the media. While the study found that transgender women tended to have more lean mass (often a proxy for muscle) than cisgender women, this extra mass did not translate into a performance advantage. When researchers tested for actual functional fitness—specifically upper and lower body strength and aerobic capacity (VO2 max)—there was no significant difference between the two groups.

Essentially, having slightly more muscle on paper did not result in being stronger or faster in practice. Bruno Gualano, a physician and co-author of the study, notes that these findings challenge the very foundation of exclusionary rules. “This refutes the logic behind blanket bans on transgender women in sports,” Gualano explains. “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.”

Understanding Hormone Therapy

The study highlights that the leveling of physical ability does not happen overnight. The meta-analysis focused specifically on transgender women who had undergone gender-affirming hormone therapy for a period ranging from one to three years. This timeline is crucial because hormone therapy works to align a person’s physiological processes with their gender identity at a cellular level.

María Miguélez González, an endocrinologist at the Gender Unit of the Gregorio Marañón Hospital, notes that time is a key factor in these physical changes. Previous research indicated that more than two years of post-pubertal hormone therapy are often necessary to significantly reduce the effects of male hormones on various physiological parameters. This recent analysis supports that view. It suggests that after a sufficient period of medical transition, the performance gap regarding strength and endurance effectively closes.

The medical community is taking note of these results, as they introduce nuance to a conversation often dominated by absolute statements. Carlos Alberto Cordente Martínez, a professor of physical activity and sports sciences at the Polytechnic University of Madrid, observes that this research challenges long-standing assumptions. “The research, which can be considered high quality, introduces doubts where, apparently, none existed before,” Martínez notes. “At the very least, this should lead us to reconsider certain maximalist positions in the field of competitive sports.” This expert consensus suggests that previous policies may have been reacting to perceived threats rather than biological realities.

The Overlooked Group: Evidence from Trans Men

Discussions about fairness in sports almost exclusively target transgender women, often leaving transgender men out of the conversation entirely. However, the new meta-analysis did not ignore this group. By examining their strength and body composition, researchers provided a more complete picture of how medical transition affects athletic performance.

The data showed that transgender men generally had less lean mass and lower upper-body strength than cisgender men. However, in these same categories, they performed better than cisgender women. This finding is critical because it demonstrates that hormone therapy effectively shifts physical capabilities. It is not just about suppressing testosterone in one group but observing how the introduction of hormones alters the body in the other.

This evidence reinforces the conclusion that current biology plays a much larger role in fitness than history. It shows that physical capacity is not permanently fixed at birth but can be significantly modified through medical intervention. Including transgender men in the analysis highlights that the physiological gap between sexes is largely driven by hormones. When those hormone levels change, the performance metrics shift accordingly, suggesting that the focus on biological sex at birth may be less relevant to fairness than previously thought.

Defining Fairness: Where Science Meets Values

Science can measure muscle mass and oxygen levels, but it cannot calculate the value of human dignity. While the data increasingly suggests that biological advantages diminish significantly with hormone therapy, the decision to include or exclude transgender athletes ultimately remains a question of ethics. Bruno Gualano, the study’s co-author, reflects that facts alone do not dictate moral actions. He points out that simply because transgender people have been historically excluded does not justify continuing that practice based on tradition alone.

“Good scientific evidence doesn’t dictate values, but it could guide how we apply them,” Gualano explains. This perspective invites sporting bodies to move away from reactive bans based on fear and toward policies grounded in reality. The current approach often penalizes a marginalized group based on assumptions that the data simply does not support. When policies are built on “shaky science” or broad generalizations, they risk undermining the very integrity they aim to protect.

Moving forward, the conversation must balance the competitive nature of women’s sports with the fundamental right to participate. The researchers emphasize that future frameworks should rely on verified physiological data rather than ideological stances. As the medical community continues to gather more specific evidence, the sporting world faces a choice. It can cling to outdated assumptions, or it can evolve to uphold the core principles of sport: fairness, inclusion, and respect for every athlete on the field. “We believe the debate should be guided by values fundamental to sport itself,” Gualano concludes, “rather than sweeping bans.”

Source:

1. Sieczkowska, S. M., Mazzolani, B. C., Coimbra, D. R., Longobardi, I., Casale, A. R., Da Hora, J. D. F. V. M. P., Roschel, H., & Gualano, B. (2026). Body composition and physical fitness in transgender versus cisgender individuals: a systematic review with meta-analysis. British Journal of Sports Medicine, 60(3), 198–210. https://doi.org/10.1136/bjsports-2025-110239