Trans Athletes: NOC-NSF Guideline & Expert Input

Scientists at Erasmus University are “not happy” with the NOC-NSF’s working method regarding a guideline published in October on the position of trans athletes. This guide, drawn up by the sports umbrella organization, should support associations in drawing up policy on the participation of trans women in top sport.

André Cats, director of top sports at NOC-NSF, writes in a foreword to that guide that research from Erasmus University reveals a “tendency” that indicates that trans women retain “a performance advantage”, even after transition and testosterone-lowering treatment. A message on the website even mentions a “clear trend”.

But scientists from Erasmus University say that is not correct. The study referred to has not yet been completed. The final version is expected in January, says professor Hub Zwart, who was ultimately responsible for the research project as dean of Erasmus University until two months ago.

NOC-NSF says in a response that the conclusions of the systematic review “known for some time [zijn]” and “very likely not anymore [gaan] change.” Black refutes that. NOC-NSF bases itself on “provisional results”, he says. According to him, the researchers recently added studies from 2025. That material sheds “another light” on the theme. This makes the picture “more complex”. The conclusions of NOC-NSF are “premature”, says Zwart. “They make something complicated very simple.”

The researchers have asked NOC-NSF to adjust the foreword of Cats, says Zwart, so that it becomes clear that the “tendency” being discussed is not based on the research that has not yet been completed. But according to him, that change has not been made. NOC-NSF is the opposite NRC does not address the question of why that request was not met. Zwart: “I would like to emphasize that the research is completely independent and is carried out carefully. That is why we are not happy with the fact that NOC-NSF prominently mentions the research in the introduction to the guide.”

Research process

NOC-NSF itself commissioned the relevant scientific study from the Erasmus Center for Sport Integrity & Transition, which is affiliated with Erasmus. The research is one systematic reviewa scientific assessment of all relevant literature on physical performance after a transition. The research process has now been running for more than two years.

It is certain that that overview does not include any research on trans top athletes. There are simply no major studies on trans top athletes. An important reason is that the group of transgender top athletes is very small. To the studies included in the systematic review non-top-athlete trans women participated, sometimes with a sporty lifestyle and sometimes not. Zwart: “On this basis it is difficult to draw conclusions about the participation of trans women in top sport.”

“There is no scientific consensus about any performance advantage of trans women in top sport,” says Lars van Leeuwen, one of the authors of the study. The evidence that trans athletes have an advantage over cis women is “small and perhaps weak.” At the same time, evidence that benefit is “completely” removed by transition and hormone treatment “may be even weaker.” There is still a lot of research missing, according to Van Leeuwen. “For example, about the influence of the age at which someone transitions, the sporting disadvantages that trans athletes experience, or sport-specific research.”

The debate about the participation of trans athletes in top sports has become highly politicized, partly due to the interference of American President Donald Trump, who signed a decree at the beginning of this year to ban transgender women from women’s sports competitions. The IOC also appears close to a decision to ban trans women from participating in all sports at the Olympic Games, although the Winter Games in Italy early next year are likely to come too soon. “Due to social debate, the relationship between clients and scientific researchers is often under pressure,” says Professor Zwart, “but thorough research takes time.”

Political sensitivities

Arnout Geeraert, assistant professor of international sports governance at Utrecht University, is critical of NOC-NSF’s working methods. “At best, there is miscommunication here. At worst, a policy choice is made that is motivated by political sensitivities,” he says. “It would have been better if NOC-NSF had had the courage to be clear and transparent. The existing research is limited, there is no scientific consensus, but this will become our policy, because sports associations ask pressing questions that need answers quickly.” That would “undoubtedly” lead to intense debate, says Geeraert, “but that is not a problem, because it is a decision with important social consequences.”

In September, Maarten Moen, chief physician of NOC-NSF, spoke de Volkskrant already about possible “performance benefits” based on the – not yet completed – research. Professor Geeraert was opposite NRC also critical about it at the time. “If, as an organization, you release information about an investigation, you must ensure that it is complete, so that outsiders can evaluate it.”

Part of a group of experts set up earlier this year is also dissatisfied with the developments surrounding the publication of the guide. This group of experts, or sounding board group, was created at the request of NOC-NSF and consists of experts in the field of inclusion, human rights and LGBTI rights in sport. André Cats refers in his foreword to the collaboration with the sounding board group and states that the guide was partly created after a “careful exploration by experts”.

But several experts have difficulty with the lack of communication from the sports umbrella organization about the conclusion of the guideline. “I generally experienced the contact with NOC-NSF as pleasant,” says Sophie Schers, who was part of the sounding board group as a policy advisor of Transgender Network. “But I have difficulty with the fact that NOC-NSF did not involve the sounding board group in the conclusion in the guide. If they had listened to the experts, they would have come to a different, less firm conclusion.” Two experts who led the sounding board group – one in the field of human rights, the other in the field of diversity – withdrew in October.

In the guide, some of the sounding board group’s conclusions have been watered down. This is what the experts stated in their latest report, in the hands of NRCthat existing studies intended to provide insight into the performance benefits of trans athletes have “significant” limitations – but that term is not found in the published guideline. While the sounding board group emphasized the prevention of exclusion and discrimination in the foreword, this theme has been moved to an appendix in the final version of NOC-NSF.

“I realize that NOC-NSF has its own guidelines,” says Sophie Schers. “But I still find it a shame that our nuanced findings do not correspond with Cats’s firm conclusion in the introduction to the guide.”

The Erasmus researchers also understand that NOC-NSF may translate the research results “into policy at their own discretion,” says Hub Zwart. “But it is important for scientists that the independence of their research is guaranteed. For us, the validity of the research is paramount, which is also important for trust in science. There is a lot of social attention for this issue, but that is precisely why quality and reliability are crucial.”

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