Transgender People in Sports: Regulations, Science, and Debate

The participation of transgender people in competitive sports represents one of the most debated issues in the contemporary sporting and social landscape. The topic sits at the intersection of physiology, law, ethics, and sports policy, and involves fundamental values such as competitive fairness and the right to inclusion. This article presents the available scientific evidence, the evolution of regulations, and the various positions in the ongoing debate.

Physiology and Athletic Performance

To understand the debate, we must start from the physiological differences between the sexes that influence athletic performance.

The Performance Gap Between the Sexes

Male puberty, driven primarily by testosterone, produces a series of physiological changes that create a measurable performance advantage. According to the consensus statement of the American College of Sports Medicine (2023), adult males on average have greater muscle mass, greater oxidative capacity, and a lower percentage of body fat compared to females [10].

The performance gap between the sexes varies by discipline: it is approximately 10-11% in middle and long-distance running at the Olympic level, reaches 17.5% in jumping events, stands at 8.9% in swimming and 8.7% in track cycling [10]. In ultra-endurance disciplines, the gap can narrow to 4.4%. In pure strength disciplines such as weightlifting, the gap can exceed 30% [10].

These differences emerge at puberty and are stable over time: a study published in PLoS ONE showed that the performance gap between the sexes has not substantially narrowed since the 1980s.

Effects of Hormone Therapy on Performance

Feminizing hormone therapy (estrogen and anti-androgens) produces significant changes in the bodies of trans women, but the scientific literature shows that not all performance-relevant parameters change to the same extent and at the same speed.

A systematic review by Harper and colleagues (2021), published in the British Journal of Sports Medicine, found that [4]:

• Hemoglobin and hematocrit levels decrease rapidly, reaching female values within a few months of starting therapy.
• Lean mass and muscle strength decrease more slowly and partially. After 36 months of therapy, non-athlete trans women still average stronger than non-athlete cisgender women.
• Structural parameters such as height, skeletal dimensions, limb length, and bone structure are not modified by hormone therapy.

Hilton and Lundberg (2021), in a review published in Sports Medicine, concluded that anthropometric parameters, muscle mass, and strength parameters superior to those achieved during male puberty are not removed by testosterone suppression, and that the male performance advantage remains substantial even after hormone therapy [2].

Evolution of IOC Rules

The International Olympic Committee (IOC) has modified its guidelines on transgender participation multiple times, reflecting the evolution of scientific knowledge and social sensitivities.

The Stockholm Consensus (2003)

In 2003, an ad hoc IOC committee convened in Stockholm established the first rules on participation for athletes who had undergone gender transition [9]. The conditions were very restrictive: complete sex reassignment surgery (including gonadectomy) was required, along with legal recognition of the acquired gender and a period of at least two years from gonadectomy before admission to competition. These rules took effect for the Athens 2004 Games.

The Stockholm Consensus was criticized for its rigidity: the surgery and legal recognition requirements effectively made participation impossible for trans athletes residing in countries without adequate legislation.

The 2015 Guidelines

In 2015, the IOC updated its guidelines, eliminating the surgical requirement. The new rules allowed trans women to participate provided that their total serum testosterone level was maintained below 10 nmol/L for at least 12 months before the first competition and throughout the duration of participation. Trans men could participate in men’s competitions without restrictions.

The 2021 Framework

In November 2021, after a two-year consultation process with over 250 athletes and stakeholders, the IOC published a new framework based on ten principles, including inclusion, non-discrimination, fairness, and absence of harm [1]. The document, titled “Framework on Fairness, Inclusion and Non-Discrimination on the Basis of Gender Identity and Sex Variations,” marked a significant shift in approach:

• No universal testosterone threshold was imposed.
• It was established that no athlete should be excluded from competition based on a presumption of advantage not supported by robust, sport-specific scientific evidence [1].
• Invasive physical examinations and unnecessary medical treatments as conditions for participation were to be avoided.
• Decision-making responsibility was delegated to individual international and national sports federations.

The 2021 Framework is not legally binding. It represents a set of guiding principles, leaving federations the task of translating them into specific regulations, with very different outcomes across disciplines.

Testosterone and Competitive Advantages: What Studies Say

The central question of the scientific debate is whether testosterone suppression eliminates the performance advantage conferred by male puberty. The results of available studies do not provide a univocal answer.

The Harper Study (2015)

Joanna Harper, a physicist and trans athlete, conducted the first study on the athletic performance of transgender athletes [5]. The study, published in the Journal of Sporting Cultures and Identities, analyzed race times of eight trans women runners, comparing performances before and after transition. Results showed an average performance decline of 17%, suggesting that trans athletes did not achieve better results than cisgender women in their age group [5].

However, the study had significant methodological limitations: only half the reported times were verified, differences in training before and after therapy were not measured, and hormonal concentrations were not assessed [5].

The Roberts et al. Study (2021)

Roberts and colleagues published in 2021 in the British Journal of Sports Medicine a retrospective study on U.S. Air Force physical fitness tests [3]. The study involved 46 trans women and 29 trans men, compared with a cisgender control group.

Results showed that before hormone therapy, trans women performed 31% more push-ups, 15% more sit-ups, and ran 1.5 miles 21% faster than cisgender women. After two years of feminizing therapy, differences in push-ups and sit-ups disappeared, but trans women were still 12% faster in running [3].

For trans men, the opposite phenomenon was observed: differences compared to cisgender men disappeared within the first year of testosterone therapy [3].

The Hilton and Lundberg Review (2021)

Hilton and Lundberg conducted a literature review published in Sports Medicine, concluding that testosterone suppression below 10 nmol/L for at least 12 months is not sufficient to eliminate the performance advantage conferred by male puberty [2]. The authors highlighted that differences in bone structure, lung capacity, heart size, and stature are not reversible through hormone therapy, and that the loss of muscle mass and strength after 12 months of therapy is approximately 5%, a value insufficient to bridge the performance gap between the sexes [2].

Limitations of Current Research

The scientific literature presents significant limitations. Available studies generally have very small samples, often involve non-athlete subjects, and rarely refer to competitive-level performance. Prospective long-term studies on elite trans athletes are lacking. Individual variability in response to hormone therapy is high, making it difficult to establish universal rules. As highlighted by a review published in Frontiers in Sports and Active Living (2023), current evidence is insufficient to draw definitive conclusions, and further research with new biomarkers and morpho-functional parameters is needed [13].

Policies of International Sports Federations

Starting from the IOC’s 2021 Framework, international sports federations have adopted very different policies, with a general trend toward stricter restrictions.

World Athletics (Track and Field)

In March 2023, World Athletics adopted the most restrictive rules among major sports federations. Trans athletes who have gone through male puberty were excluded from women’s competitions at the international level [6]. President Sebastian Coe stated that, in the absence of sport-specific scientific evidence and with no trans athletes competing at the international level at that time, the Council had decided to prioritize fairness and integrity of women’s competition over inclusion. A working group was established to re-examine the issue within 12 months [6].

For athletes with differences of sex development (DSD), such as the case of Caster Semenya, the new regulations require maintaining testosterone levels below 2.5 nmol/L for a minimum of 24 months to compete in any women’s event at the international level [6].

World Aquatics (Swimming)

In June 2022, the international swimming federation (then FINA, now World Aquatics) approved a policy allowing trans women to compete in the women’s category only if they can demonstrate they have not gone through any stage of male puberty beyond Tanner stage 2, or before age 12 [7]. In practice, only athletes who started puberty suppression before the onset of male puberty can compete in the women’s category.

The policy, approved with 71.5% of member votes, also provided for the creation of an open category, open to all regardless of sex, legal gender, or gender identity [7]. In 2023, World Aquatics launched the open category at the Swimming World Cup.

World Rugby

In 2020, World Rugby became the first major sports federation to ban trans women’s participation in women’s competitions at all levels, not just internationally [12]. The decision was primarily motivated by safety concerns: biomechanical studies commissioned by the federation indicated that trans women players generate forces on head and neck 20-30% greater than elite cisgender players, due solely to the difference in body mass [12].

The policy met strong opposition: the national federations of New Zealand, England, Canada, the United States, and Australia expressed disagreement with the ban, and some declared they would not enforce it at the national level.

UCI (Cycling)

In July 2023, the Union Cycliste Internationale (UCI) banned trans women who have gone through male puberty from women’s competitions on the international calendar across all categories and disciplines [8]. The UCI’s management committee stated that current scientific knowledge does not confirm that at least two years of hormone therapy with a plasma testosterone target of 2.5 nmol/L is sufficient to completely eliminate the advantages of male puberty [8]. The men’s category was renamed “men/open” to accommodate athletes excluded from the women’s category.

FIFA (Soccer)

FIFA has not yet published a definitive updated policy. The federation has declared it is in the process of reviewing its gender eligibility regulations, in consultation with experts. Existing rules require trans women to demonstrate testosterone levels in the female range for an adequate period, with annual verifications. In 2023, Quinn, a Canadian non-binary footballer, became the first openly transgender person to participate in a FIFA Women’s World Cup. Some national federations, such as Germany’s DFB, have introduced policies allowing trans and non-binary people to choose whether to play on men’s or women’s teams at amateur and youth levels.

Summary Overview

Federation policies fall along a spectrum ranging from complete exclusion from the women’s category (World Athletics, World Rugby, UCI) to conditional participation tied to hormonal thresholds (FIFA, under old rules), to a principle-based approach without universal thresholds (IOC 2021 Framework) [1]. The dominant trend in the 2022-2023 period was toward stricter restrictions, with many federations opting to exclude trans women who have gone through male puberty [6][7][8].

The Current Debate

The debate about transgender participation in sports involves questions of sporting fairness, human rights, social inclusion, and body politics. The main positions can be summarized as follows.

The Competitive Fairness Argument

Those who support the need for stricter restrictions argue that physiological differences conferred by male puberty are not fully reversible through hormone therapy, creating an unfair competitive advantage for trans women in the women’s category [2]. This position draws on studies showing the retention of residual advantages in strength, speed, and body size even after years of therapy [2][3].

Proponents of this position emphasize that the women’s category in sports exists specifically to guarantee equal competitive opportunity for cisgender women, and that unrestricted inclusion could compromise the fairness of that category. Some organizations, such as the Women’s Sports Policy Working Group, propose that sports policies should prioritize the protection of women’s competition.

The Inclusion Argument

Critics of restrictive policies point out that the number of trans athletes at the competitive level is extremely small and that there is no case history of systematic domination of women’s competitions by trans athletes. Organizations such as Human Rights Watch and Athlete Ally highlight that exclusion from sports has significant consequences on the mental health and well-being of trans people, and that restrictive policies can expose athletes to discrimination and stigmatization.

Inclusion advocates also note that the natural variability within the women’s category (differences in height, wingspan, lung capacity, hormone levels) is broad, and that even among cisgender women significant individual biological advantages exist that are not regulated. From this perspective, isolating a single parameter like testosterone as an admission threshold is a simplification that does not reflect the complexity of athletic performance.

Alternative Proposals: Open Categories

A solution proposed by several federations is the creation of open categories, open to all regardless of sex or gender identity. World Aquatics and the UCI have already implemented versions of this model, with a dedicated open category and the renaming of the men’s category to “men/open,” respectively [7][8]. The United States Olympic and Paralympic Committee (USOPC) has encouraged sports federations to consider adopting open categories.

Critics of this proposal note that, given the extremely small number of trans athletes at the competitive level, a separate category would not be able to ensure meaningful competition. Additionally, relegating trans athletes to a separate category is seen by some as a form of segregation that prevents trans people from competing in line with their gender identity.

The State of the Discussion

The debate remains open and evolving. Current scientific evidence does not allow for determining with certainty whether and to what extent hormone therapy eliminates the performance advantages conferred by male puberty, especially at the elite sport level [13]. The research has significant gaps: small samples, absence of studies on elite athletes, high individual variability, and lack of long-term data [13].

Sports federations find themselves balancing two potentially competing demands: protecting competitive fairness in the women’s category and respecting the right of trans people to participate in sports consistent with their identity. The choices made so far reflect different priorities and different interpretations of available evidence. The continuation of scientific research and dialogue among all stakeholders remain essential conditions for ever more informed and respectful policies for all athletes involved.