Transgender athletes or athletes with a DSD: science and the need for fair and sensible regulations

Kym Fraser, Katharine Kilroy and Alana Hudson
26 Apr 2023
Time to read: 6 minutes

While the question of transgender and DSD athlete participation in female sporting competitions is undeniably controversial, the history of athletics regulations in the last decade has demonstrated the importance of providing evidence and justification for eligibility restrictions.

On 24 March 2023, the World Athletics Council (WAC) (previously the International Association of Athletics Federations or IAAF) announced new regulations for transgender athletes or athletes with a Difference of Sexual Development (DSD) (2023 Regulations). These regulations directly impact the eligibility of these athletes to compete in the female category at the international level.

In sum, the WAC:

  • has banned male-to-female transgender athletes who have undergone male puberty; and
  • will now require DSD athletes to reduce their testosterone levels below 2.5 nmol/L for at least six months (with this period extended to 24 months in 'previously restricted' events).

The decision marks the latest stage in attempts to regulate access to the female category of sporting competition. The last decade or so has seen a particularly contentious debate emerge over regulation of the participation of athletes by reference to testosterone levels, with the Court of Arbitration for Sport (CAS) suspending previous regulations for lack of evidence of an advantage.

As it is unclear on what scientific basis the WAC has made this most recent decision, there is a real question as to whether the 2023 Regulations are similarly vulnerable to challenge by transgender or DSD athletes.

An evolving position

Gatekeeping of the female category can be traced to the beginning of regulated female sport, with the use of testosterone levels as a metric for assessing eligibility a relatively recent development.

Recent history has seen the identification of testosterone as a basis for eligibility, with threshold requirements initially set at 10 nmol/L:

  • in 2003, the International Olympic Committee (IOC) issued a statement on "sex reassignment in sports", noting that eligibility would be (in part) dependant on appropriate hormonal therapy having been administered "for a sufficient length of time to minimise gender-related advantages in sport competitions";
  • in 2011, the IAAF issued a policy on hyperandrogenism, which specified that athletes would be disqualified from female competition if their testosterone levels rose above 10 nmol/L, and they were not otherwise insensitive to androgens (meaning their body does not respond to testosterone) (IAAF 2011 Regulations); and
  • in 2015, the IOC issued guidelines which required that an athlete must demonstrate that her total testosterone level in serum has been below 10 nmol/L for at least 12 months prior to her first competition and that she must maintain that level throughout the period of desired eligibility for competition.

The development of these guidelines provided the basis of what appeared to be an emerging consensus on testosterone levels as an indicator of advantage for transgender and DSD athletes, and as something that should be controlled to ensure a fair competition. However, there has also been a more recent trend towards total bans on male-to-female transgender athletes who have experienced male puberty, as evidenced by the 2023 Regulations released by the WAC. Other bodies that have introduced similar rules include World Aquatics (formerly FINA) and World Rugby, and have cited concerns about unfair advantage and the potential for transgender women to cause serious injuries to cisgender women. Some commentators have questioned the availability of scientific evidence to such policies, stating that "at present, no data suggests safety in women's sport is compromised by including trans women".

By contrast, some domestic codes have sought to develop policies to facilitate the inclusion of transgender and gender-diverse athletes in elite sport. For example, the Football Federation of Australia has announced its commitment to supporting the inclusion of transgender and gender-diverse people in football through the development of a High-Performance Inclusion Policy. The Australian Football League has also sought to codify when a male-to-female transgender athlete may be eligible to participate in the AFLW (although that policy appears, at least. questionable in terms of the metrics used to assess eligibility).

Challenging the consensus

In 2014, Indian sprinter Dutee Chand was subjected to a "gender verification" test by the Athletics Federation of India, after questions were raised about her physique and impressive competition performance. The test identified Chand as having testosterone levels above the 10nml/L level set by the IAAF 2011 Regulations and being an athlete with a DSD. As such, she was deemed ineligible to compete.

Chand challenged the IAAF 2011 Regulations at CAS. In 2015, CAS determined that there was insufficient scientific evidence supporting a link between enhanced testosterone levels and improved athletic performance, and suspended the IAAF 2011 Regulations. The IAAF was given two years to produce relevant evidence, otherwise the IAAF 2011 Regulations were to be declared void.

In 2017, the IAAF produced a report that found elevated testosterone levels advantaged female athletes by margins of between 1.78% and 4.53% in middle distance running, hammer throw and pole vault. No impact was noted in any other competition or in any men's category events.

In 2018, off the back of this report, the IAAF issued new regulations (2018 IAAF Regulations). These stipulated that a DSD athlete was restricted from competing in middle distance (400m-1 mile) running events (Restricted Events) unless they had circulating testosterone levels of 5nmol/L or below and were able to maintain those levels for at least six months prior to competing (and continuously thereafter).

In 2019, Caster Semenya, a middle-distance runner from South Africa and DSD athlete, challenged the 2018 IAAF Regulations on the basis that they were discriminatory, not necessary, and not reasonable and not proportionate. Under the 2018 IAAF Regulations, Semenya was ineligible to compete in the Restricted Events without taking medication or undergoing surgery.

Unlike Chand, however, Semenya's challenge was unsuccessful. CAS upheld the 2018 IAAF Regulations, finding that they were discriminatory but necessary, reasonable and proportionate to achieve fair competition in the female category. Nevertheless, CAS questioned the strength of the evidence in respect of some of the proposed Restricted Events and suggested the IAAF consider withholding implementation of its regulations until further evidence could be obtained. The IAAF rejected this suggestion.

Semenya has sought to appeal this decision, first in the Federal Supreme Court of Switzerland (which was unsuccessful) and now in the European Court of Human Rights (decision pending).

Continuing paucity of evidence

The question of how transgender and DSD female athletes perform against cisgender, non-DSD female athletes has been the subject of increasing debate in recent years. However, that has not corresponded to significant scientific study of the question. As noted above, the IAAF itself declined CAS' recommendation to obtain additional evidence regarding the impact of elevated testosterone on athletic performance.

Perhaps most relevantly, a 2021 study in the British Journal of Sports Medicine suggests that transgender women maintain an athletic advantage over their cisgender peers even after a year of hormone therapy. The study found that prior to taking female hormones, trans women performed 31% more push-ups and 15% more sit-ups in one minute, and ran 1.5 miles 21% faster than their cisgender peers. After two years of hormone therapy, the push-up and sit-up differences disappeared, however the trans women were still 12% faster.

However, the study involved a sample size of only 46 transgender women and focussed on armed forces personnel, as opposed to athletes and sporting performance generally. As such, it is unclear how or whether the findings can be applied to particular sports, or whether the sample size is large enough to draw accurate and broadly applicable conclusions. Similar criticisms can also be raised over a 2019 Swedish study, which found that thigh muscle mass was reduced, albeit marginally, after 12 months of hormone treatment. However, this study followed just 11 transgender women and only assessed muscle mass in the thigh and knee.

As such, it is difficult to say that there is conclusive evidence of widespread or universal advantage resulting from elevated testosterone. Associate Professor Ada Cheung, an endocrinologist at Austin Health who also leads the Trans Health Research Group at the University of Melbourne, has said that when it comes to transgender health there is "not a lot of evidence, but plenty of assumptions". Cheung also says that "no long-term research with adequate comparison groups (adjusted for height) has examined the impact of hormone therapy on strength, fitness and endurance" and that, while larger stature is possibly an advantage for some sports, it's equally possible that a transgender women with a larger stature and smaller muscle mass may actually be at a disadvantage.

Viability of 2023 Regulations

The 2023 Regulations mark a significant shift in the regulation of female eligibility. Firstly, the regulations again lower the testosterone levels permitted, second, they apply to all events (and not just Restricted Events) and third, they exclude transgender athletes completely. A summary of the evolving regulations is illustrated in the table below.


Permitted testosterone

Event applicability

2011 IAAF Regulations

10 nmol/L

All events

2018 IAAF Regulations

5 nmol/L

Restricted Events only

2023 Regulations

2.5 nmol/L

All events


For the past five years, restrictions on eligibility were limited to the Restricted Events, where evidence of an athletic advantage had been accepted by CAS. The absence of such evidence was the reason the 2011 IAAF Regulations were suspended and the 2018 IAAF Regulations were limited in scope.

In its press release of 24 March 2023, announcing the 2023 Regulations, the WAC said:

"World Athletics has more than ten years of research and evidence of the physical advantages that these athletes bring to the female category."

With no reports, studies or specific evidence cited, it's unclear what the WAC has relied to support the shift and, indeed, whether it has the evidence CAS may require.

In relation to the ban of transgender athletes, WAC has acknowledged that:

"there are currently no transgender athletes competing internationally in athletics and consequently no athletics specific evidence of the impact these athletes would have on the fairness of female competition in athletics."

However WAC noted that in the circumstances, it had decided to "prioritise fairness and the integrity of the female competition before inclusion".

The importance of evidence

While the question of transgender and DSD athlete participation in female sporting competitions is undeniably controversial, the history of athletics regulations in the last decade has demonstrated the importance of providing evidence and justification for eligibility restrictions.

It is critical to remember, as sporting federations grapple with the questions of fairness and inclusion when determining whether to allow transgender or DSD athletes to compete – while emotive, such decisions need to be made by reference to available evidence, otherwise they are, and will remain, vulnerable to challenge.

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