The International Olympic Committee (IOC) announced a new policy this week on the eligibility for the women’s category in the Olympic Games, limiting participation to “biological females” and thus excluding transgender and intersex people, among others.

According to the IOC, its rationale was ensuring “fairness, safety and integrity in elite competition” and “protection of the female (women’s) category”.

The policy will apply in the 2028 Olympics in the United States. Notably, in 2025, US President Donald Trump signed an executive order for the IOC to amend standards, “ensuring that eligibility for participation in women’s sporting events is determined according to sex and not gender identity or testosterone reduction.”

The participation of trans women and those having characteristics like higher testosterone levels in women’s sports has long been a subject of polarising debate. The 2024 Paris Olympics saw considerable controversy over gold medallist boxer Imane Khelif, with many people incorrectly identifying her as a trans woman.

Here is a look at the policy and its criticisms in the context of the larger debate.

What exactly are these distinctions of sex and gender?

Reviewing its 2021 eligibility policy, the IOC said it took comments from experts across fields — sports science, endocrinology, transgender medicine, sports medicine, women’s health, ethics and law — and female athletes. It said the broad consensus was for inclusion in the “Female Category” to be based on biological sex.

At this stage, it is important to distinguish between the concepts of “sex” and “gender”. As the IOC itself notes, sex (male/female/intersex) is the distinction based on reproductive biology.

Sex is determined based on chromosomes, which carry genes. Humans have 23 pairs of chromosomes — 22 are identical in men and women; one, the sex chromosome, is different. The XX sex chromosomes result in the development of female sex organs, and XY in male sex organs.

Intersex people have variations which do not fit this binary. Crucially, some people born with female reproductive organs may also carry the XY chromosome, in what is known as Swyer syndrome, one of many “Disorders of Sex Development”, or DSDs. South African athlete Caster Semenya, who has a DSD, has gone to court over policies barring her from participating unless she suppresses her testosterone levels.

Gender, however, is a social construct — It is “a person’s sense of themselves as a woman or a man or neither/non-binary,” as the IOC says. Gender identification can be different from sex. For example, a transgender woman may have been born with male sex characteristics, but identify as a woman.

Modern sports are organised based on sex, with men and women competing in different categories. This is because men, on average, have certain physiological advantages over women.

The SRY gene, found on the Y chromosome, is responsible for testosterone production. Multiple studies have attempted to decode how the hormone affects physical characteristics. A 2017 paper (‘Circulating Testosterone as the Hormonal Basis of Sex Differences in Athletic Performance’) published in the journal Endocrine Reviews supported the link between testosterone and athletic performance.

“The available, albeit incomplete, evidence makes it highly likely that the sex difference in circulating testosterone of adults explains most, if not all, the sex differences in sporting performance,” it said. This is due to the effect of testosterone in increasing “muscle mass and strength, bone size and strength (density), and circulating haemoglobin”. Other studies note that the data available is inadequate.

The new IOC policy said that such differences lead to a 10 to 20% performance gap between male and female athletes, depending on the sport (lifting, punching, throwing and jumping seeing the sharpest difference). However, it noted that “The extent of the performance advantage (and its implications) varies across sports and events and from occasion to occasion, depending on the athletes involved.”

At the end of the day, a lot remains unknown about the impact of testosterone on sporting performance. Many question if the case of women who are born with higher levels of testosterone is any different from that of people with other genetic advantages, like basketball great LeBron James’ height or swimming champion Michael Phelps’ massive fin-like hands.

This is at the heart of the debate surrounding gender eligibility in women’s sports. Many argue that to prevent some athletes from having an unfair advantage in women’s sports, women with DSDs, which facilitate greater testosterone production, must not be allowed to compete with other women.

The new IOC policy says that “Including athletes who are XY transgender and/or androgen-sensitive XY-DSD athletes (whatever their legal sex or gender identity) in the Female Category in sports and events that rely on strength, power and/or endurance runs fundamentally counter to ensuring fairness, safety and integrity in elite competition.”

What could the wider ramifications be?

In 2021, the IOC decided to leave it to international sports federations to develop their own set of eligibility rules, based on an “evidence-based approach”, while keeping in mind principles of “fairness”, “inclusion”, “non-discrimination”, “no presumption of advantage”, and “prevention of harm”. Previously, it took into account testosterone levels, to be below 10 nanomoles per litre (nmol/L) for trans women athletes (who had transitioned from male to female).

However, the latest shift will likely drive a global change. The IOC has said the new policy “shall be adopted by International Federations and other sports governing bodies, such as National Olympic Committees (“NOCs”), National Federations and Continental Associations (“SGBs”), when exercising their responsibility in implementing eligibility rules in relation to IOC Events.”

World Athletics previously used testosterone levels as an eligibility determinant. DSD athletes need to keep their testosterone level below 2.5 nmol/L for at least 24 months before they become eligible to participate in any event. Last year, it introduced a one-off SRY gene test for all female athletes ahead of the World Championships in Tokyo, Reuters reported.

FINA, the world swimming body, the International Cycling Union, and the International Rugby Union have all instituted varying degrees of bans on trans women athletes in recent years, linked to testosterone levels.

The need for such bans has been questioned, also given the different skills required across sports. An “open category”, specifically for trans athletes, has been suggested, but may have difficulties given the small number of elite-level trans athletes.

Many have described the debate as a battle between inclusion (of all women, no matter their biological differences) and fairness (for women who do not have high levels of testosterone). It has garnered further attention as issues related to diverse gender and sexual identities have become ideological battlegrounds in politics in recent years.

LGBTQ+ charity Stonewall said in a statement, “Sport has a unique power to bring people together… Today’s decision will be one that stokes further division in our increasingly polarised world. Considerations of safety and fairness should always sit at the heart of sporting competition; but there will undoubtedly be an unintended ripple effect across community and grassroot sports, where many trans people, young and old, will hear the message they are unwelcome and that sport is not a place for them.”