Physical fitness of transgender women ‘comparable’ to that of other women

Transgender women have comparable fitness to those whose birth sex is female, research has suggested.

The study, published in the British Journal of Sports Medicine, says current evidence challenges “assumptions” about trans women having inherent advantages in sport.

Last April, the UK Supreme Court ruled that the legal definition of a woman is based on biological sex.

As a result, many sports banned trans women from taking part in games involving those whose biological sex is female, including cricket and football.

Some sports – such as cycling and triathlon – had already introduced an open category for trans athletes.

The International Olympic Committee also set up four working groups last summer, including one for the protection of women’s sport.

In the latest study, researchers from the University of Sao Paulo in Brazil said “the inclusion of transgender women in female sports categories remains highly contentious”.

They found that while gender-affirming hormone therapy (GAHT) has been shown to potentially alter body composition in transgender people, the “evidence on functional performance outcomes remains inconsistent”.

To look at this issue, researchers examined 52 existing studies on 6,485 people and compared the body composition and fitness differences between transgender women and those whose birth sex is female.

The overall study included 2,943 transgender women, 2,309 transgender men, and 568 women and and 665 men whose gender identity matches the sex they were assigned at birth (cisgender).

Transgender women had more lean mass, a proxy for muscle, but had no observable differences to cisgender women in upper or lower body strength, or in maximal oxygen consumption, a key measure of cardiorespiratory fitness.

Transgender women’s upper and lower body strength and their respiratory fitness markers were also all much lower than in cisgender men.

The team concluded that “despite persistent differences in absolute lean mass, transgender women do not exhibit significant differences in upper-body strength, lower-body strength or maximal oxygen consumption relative to cisgender women after one to three years of gender-affirming hormone therapy”.

They added: “This review demonstrates that functional performance in transgender women converges toward cisgender women over time, challenging assumptions about inherent or GAHT-resistant athletic advantages and strengthening the evidence base for sport policy deliberations.”

The authors said current evidence on the issue is of variable quality.

Few studies included a broad spectrum of ages, types of sport and competitive levels, they added.

However, they said the evidence does not back up “prevailing theories” about the inherent athletic advantage of transgender women.

The team added “the current data do not justify blanket bans” but called for more research.

“Ideally, to resolve speculation, future long-term, longitudinal studies should prioritise performance-specific metrics in transgender athletes,” they said.

“However, one should be aware of the scarce number of transgender athletes, particularly in the elite sport.”

Fiona McAnena, director of campaigns at sex-based rights charity Sex Matters, said: “Men do not shrink or magically lose all their male advantages when they identify as women, no matter what hormones they take.

“Everyone knows no one can change sex, and no academic analysis or statistical data tricks can prove that men should be allowed to compete in women’s sport based on a claimed female identity.

“The males in this study may have hobbled their own athletic prowess voluntarily by suppressing their testosterone but that is not an argument for forcing female athletes to compete with them.”

Dr Blair Hamilton, research associate in applied sport and exercise physiology at Manchester Metropolitan University, welcomed the study.

“Overall, the findings make sense and are consistent with what we’ve seen in the wider scientific literature and in my own research, although there is fierce debate in this area,” they said.

“The review also highlights something important: you can’t assume that having slightly more muscle automatically means having better sporting performance, because the studies measuring muscle size and those measuring performance weren’t always done on the same groups of people.

“These conclusions match what we found in our 2025 systematic review, where transgender women had more body fat, less fat‑free mass, and lower strength than cisgender men, meaning that comparing transgender women to cisgender men isn’t a fair or meaningful comparison.”

Dr Hamilton said to know how something affects elite athletes, “you really need elite athletes to study, and at the moment, there are very few openly transgender elite athletes anywhere in the world”.

“This is partly due to the changing sporting climate. In the UK, after recent legal decisions, and in the USA under new federal restrictions, fewer transgender people can access sport at all, let alone reach elite level.

“Because of that, we simply don’t have the numbers needed to make strong, sport‑specific conclusions at the elite end.

“What this paper does reinforce is that the things often labelled as ‘retained advantages’, such as height and lean mass, don’t directly translate into performance simply or predictably.”