Women's sport and single-sex spaces

What is the evidence on male advantage in sport and the case for single-sex provision?

Women’s sport is sex-segregated because male puberty creates average physical advantages which would otherwise make it substantially harder for female athletes to win, qualify, retain places or receive sporting rewards. The issue is not whether every male is stronger or faster than every female. Individual overlap exists. The question for sporting categories is whether a class of athletes who have undergone male puberty has attributes that, on average and at the performance extremes, undermine a category created to compensate for sex-based disadvantage.

Background

Women’s sport is sex-segregated because male puberty creates average physical advantages which would otherwise make it substantially harder for female athletes to win, qualify, retain places or receive sporting rewards. The issue is not whether every male is stronger or faster than every female. Individual overlap exists. The question for sporting categories is whether a class of athletes who have undergone male puberty has attributes that, on average and at the performance extremes, undermine a category created to compensate for sex-based disadvantage.

Those attributes are not reducible to one blood-test result. Male puberty affects height, skeletal dimensions, muscle mass, muscle fibre size, heart and lung capacity, haemoglobin, body composition and leverage. The American College of Sports Medicine’s 2023 consensus statement concluded that, in events dependent on endurance, muscular strength, speed and power, males generally outperform females by 10–30%. It identifies puberty as the point at which the substantial performance gap emerges.

Policy debates commonly combine two separate questions. The first concerns sporting fairness and, in some sports, physical safety. The second concerns toilets, changing rooms, hospital wards, domestic-abuse services, refuges and other single-sex provision. Both involve sex as a material category, but the legal purpose, practical setting and relevant evidence differ. A sprint final is not a rape-crisis service; neither should be governed by slogans.

What the documents say

Sport science and hormone treatment

Harper and colleagues’ systematic review in the British Journal of Sports Medicine reviewed 24 studies published between 1999 and 2020 on trans women receiving testosterone-suppressing hormone treatment. It found that haemoglobin and haematocrit fell comparatively quickly, reaching levels equivalent to those of non-trans women after around four months. Measures of lean body mass, muscle area and strength declined more gradually. However, the review reported that these measures remained above those observed in non-trans women after 36 months of treatment. The authors also noted limited evidence, particularly on trained and elite athletes (Harper et al., 2021).

This limitation matters. Evidence from clinical cohorts cannot simply be converted into a precise performance rule for every sport. Performance depends on discipline, training, technique, age, body size, competitive level and the demands of the event. But limited sport-specific evidence does not mean there is no relevant evidence. The broad male performance advantage and the enduring effects of male puberty are independently documented in physiology and performance research.

In 2023, the American College of Sports Medicine consensus statement described biological sex as a primary determinant of athletic performance. It concluded that male advantages are rooted in anatomy and physiology shaped by sex chromosomes and sex steroids, particularly the large rise in testosterone during male puberty. It also emphasised that the size of the performance gap varies by event: upper-body power events tend to show larger gaps, while some ultra-endurance events show smaller ones.

Rules adopted by sporting bodies

International federations have not reached one uniform answer. World Aquatics, then known as FINA, adopted a gender-inclusion policy on 19 June 2022. Its approach was based on whether an athlete had experienced male puberty beyond Tanner Stage 2 or before age 12, whichever was later. World Athletics followed on 23 March 2023, announcing that transgender women who had experienced male puberty would be excluded from female World Rankings competition from 31 March 2023.

These decisions were not findings that trans people should be excluded from sport generally. World Athletics stated that it wanted to preserve opportunities for transgender athletes while protecting fairness in the female category, and announced an open category as part of its approach. The policy question is therefore not participation versus exclusion in the abstract; it is which categories accurately serve distinct purposes.

Single-sex services and UK law

The Equality Act 2010 is relevant internationally as an influential legal framework, though it applies only in Great Britain. Schedule 3 permits separate services for women and men, services provided differently to each sex, and services provided only to one sex in specified circumstances. The core legal tests include whether separate or single-sex provision is a proportionate means of achieving a legitimate aim, such as privacy, decency, trauma-informed care, safety or effective service delivery.

On 16 April 2025, the UK Supreme Court gave judgment in For Women Scotland Ltd v Scottish Ministers. It held that the terms “sex”, “woman” and “man” in the Equality Act refer to biological sex. The Court also stressed that this conclusion did not remove protections from trans people: gender reassignment remains a protected characteristic under the Act. In legal terms, the judgment addressed statutory interpretation; it did not authorise harassment, hostility or arbitrary treatment of trans people.

The positions

The inclusion-focused position argues that trans people should be able to participate in sport and access public life without humiliation or blanket exclusion. Supporters often argue that sport should assess genuine, sport-specific evidence rather than rely on assumptions; that testosterone suppression changes relevant physiology; and that policies should account for the small number of affected athletes, especially at recreational level. The International Olympic Committee’s 2021 framework urged sporting bodies not to presume an advantage solely from transgender status and to develop evidence-informed, sport-specific rules.

The sex-based position argues that female sport exists precisely because male puberty produces a class-wide sporting advantage that cannot be reliably neutralised by adult hormone treatment. It maintains that a female category must have objective sex-based boundaries if it is to remain meaningful, particularly in elite competition, contact sports, selection pathways and record-keeping. On this account, inclusion should be pursued through an open or mixed category, additional participation routes and respectful administration, not by redefining the female category around gender identity.

For single-sex spaces, an inclusion-focused position emphasises the dignity and practical needs of trans people, including the risk of harassment when they are denied ordinary facilities. A sex-based position emphasises that women and girls may require boundaries based on sex, rather than identity, for privacy, safeguarding and trauma recovery. UK equality law attempts to address this tension through proportionality rather than a universal rule for every setting.

Interpretation

Beyond Gender’s reading is that the evidence supports retaining a clearly sex-based female sporting category after male puberty. This is an interpretation, not a claim that every individual case is identical. Yet categories are not built around exceptional cases. They exist because average, population-level differences become decisive in competitive environments where small margins determine medals, teams, scholarships, records and income.

The evidence also suggests that testosterone alone is an inadequate proxy for sex in sport. Hormone treatment can alter some important traits, including haemoglobin, but current evidence does not show that it reverses all performance-relevant effects of male puberty. A rule based solely on present testosterone levels therefore risks treating a complex developmental history as though it were a single laboratory measurement.

Similarly, single-sex provision should not be portrayed as an expression of animus. Privacy, bodily dignity, safeguarding and effective trauma services are legitimate reasons for sex-based boundaries. Respect for trans people and acknowledgement of sex-based needs should be pursued together. In practice, that means clear rules, courteous communication and, where feasible, genuinely private or additional facilities rather than forcing women to surrender sex-based provision.

Open questions

More high-quality research is needed on trained transgender athletes across specific sports, ages and durations of hormone treatment. Existing studies often involve small samples, non-elite participants and measurements of physiology rather than competition outcomes. Better evidence may refine policies, especially in sports where endurance, contact, height, strength or power matter in different combinations.

There is also a practical question about category design. Open categories may widen participation in principle, but their uptake, funding, competitive structure and viability remain uncertain. Recreational sport presents different considerations from international sport, and childhood sport differs from adult competition after puberty. Policies should therefore distinguish age, level, sport and safety risk rather than assume that one answer fits all contexts.

For services, the continuing challenge is implementation. Organisations need rules that are lawful, intelligible and workable for staff and users. They should be able to preserve single-sex provision where justified, while avoiding needless confrontation and providing respectful alternatives where possible. The most durable approach is one that states plainly what a service is for, what boundary it uses and how it will meet competing needs.

On the timeline

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