Transgender People Playing Sports: What Are the Scientific Facts?

The rights of transgender people across this country are under attack. There are now over 400 pieces of legislation across the US that aim to limit the rights of transgender people to get medical treatment, use public restrooms, and play sports.

According to the ACLU, 220 out of 469 of these bills currently target youths attending school. In particular, many aim to ban transgender youth from participating in school sports. Transgender athletes continue to be a huge source of controversy and debate around the world. Many people have voiced strong opinions over the last decade about under what circumstances transgender and intersex athletes should be able to compete — or if they should be allowed to compete at all.

As a result, nearly every sports governing body has been forced to weigh in on the question, including the International Olympic Committee (IOC), which has a major influence over other organizations. The IOC has come out with two official sets of guidelines regarding transgender and intersex athletes so far — once in 2015, and more recently in 2021.

So, why are we still so confused and divided about who can compete? And why are state legislatures trying to take matters into their own hands, instead of listening to the guidance of the IOC, national sports governing bodies, or their city and school governments?

The Lie About Puberty

One contributing factor is the sheer number of op-eds devoid of medical and scientific facts, which work to further obscure the truth. One example is a 2022 Washington Post piece by swimmer Diana Nyad. Her article refers to trans women as people “who have experienced male puberty” multiple times. The fact that she pulls our focus several times over the course of the article towards the experience of puberty, even though the subject of her attacks is a college athlete, is the first giveaway that this article is not based in science.

Medically speaking, there are many things that happen to bodies, beginning during puberty, as the result of sex hormones. However, many of these changes are halted or reversed during the course of gender affirming medical therapy, particularly those that affect sports performance. Therefore, the focus on what has happened in an athletes past is of little use in determining their athletic ability as an adult, and is simply a discriminatory hedge. Scholars further speculate that transwomen, who might be bigger in stature, are now carrying those same frames with less muscle and endurance, as a result of their suppressed testosterone. This could actually lead to an athletic disadvantage.

Nyad goes on to claim that there is an achievement gap of “a huge 10 to 12 percent” between all male and female athletes, which is also false. In contrast, the IOC itself acknowledges that there is significant variation from sport to sport; hence the reason that it’s 2021 guidelines are actually not guidelines at all, but rather instruct each individual sport to determine their own inclusion guidelines. Rockclimbing is an example of a sport with narrow gender parity, and high levels of female excellence.

Fake News

The Post was forced to correct a lie from it’s first edition — Nyad had initially claimed that Lia Thomas swam faster in 2022 that any female college athlete “in history” — which is not true. This lie paints a starkly different picture from reality, and leaves the reader with a very skewed impression of the truth. Other falsehoods include stating that men’s bigger hands allow them to handle “a ball” better, and that narrower hips have more “efficient movement dynamics.” Such a sexist reading of the sports landscape is unfortunately what defines so much of the conversation around trans athletes today, which really serves no one and does not advance understanding.

Mainstream news reporting is also to blame. Recently, nearly 1,000 New York Times contributors signed an open letter, alleging that the Times has consistently disregarded it’s own journalistic standards in the reporting of transgender issues. They claim that the basic humanity of transgender people was not affirmed in their coverage on a regular basis, and point to evidence that New York Times articles have been cited in efforts at anti-trans legislation. They claim that transgender youth in particular have been regularly de-humanized and the science minimized or ignored, in favor of sensationalist headlines that question the basic rights of transgender youth as American citizens.

No Guidance From the IOC

You read that right earlier — the current IOC guidelines actually make no concrete suggestions at all regarding medical testing to determine eligibility to compete in gender-segregated sports. Interestingly, there is no mention at all of using testosterone levels as criteria – which its 2015 guidelines were very specific about.

Indeed, the 2015 guidelines informed the way that many sports governing bodies in the US and around the world still use to decide if a transgender or intersex athlete is eligible to participate, particularly using the measure of testosterone levels (and requiring they be “below 10 nmol/L for at least 12 months prior to her first competition” for women). In contrast, the 2021 guidelines introduce nothing but more confusion; simply stating that all governing bodies are responsible for creating their own standards, and that the process should be fair and equitable.

It’s easy to tell people they ought act fairly and equitably. But does this create results? The fact is that the IOC document cites no medical papers or facts, and gives no advice at all apart from “please play nice.” No wonder we are all confused.

Testosterone – What Does it Do, and Not Do?

So, athletically speaking, what are the physiological advantages that some people can have over others, that are associated with gender?

It largely boils down to testosterone. However, we must take care not to reduce what is a complex question down to one lab value. Everyone’s body responds to testosterone differently, with studies profiling athletes seen as male who tested at under 10 nmol/L (below the IOC’s criteria for determining gender), and female athletes (cisgender, and without intersex conditions) who tested over 10 nmol/L. These studies make clear that there is not a direct correlation between testosterone levels and athleticism. If that were true, all men would be ripped and toned.

Yet, testosterone does have measurable effects. So, what exactly does testosterone do? Testosterone raises red blood cell counts. Red blood cells (RBCs) are responsible for transporting oxygen to our muscles, and so increased RBCs mean we can perform harder, for longer — also referred to as endurance.

Testosterone also increases muscle mass. However, genetics is also a huge factor in the development of muscle mass, and there is not a direct line from testosterone to big muscles. Everyone’s body is different. Some people’s genetics lead to easy muscle gain, and other’s don’t.

Transgender Women Suppress Testosterone

It is important to note that suppression of testosterone (which is part of the standard treatment regimen for transgender women) decreases muscle mass and RBC counts, which leads to poorer athletic performance for most. As with all transgender science, more research is needed to fully understand the effects of hormone therapy on a wide segment of the population over time. Good science takes a long time, and transgender people have not had access to affirming treatments for very long. However, scholars agree that the available evidence shows that suppressing testosterone affects performance.

So, testosterone has measurable effects, but it is not a perfect measure of ability. What, then, to do about transgender, non-binary and intersex people who want to compete in sports that are segregated by gender?

Trans Athletes Already Compete

Lia Thomas, collegiate swimmer and the subject of Diana Nyad’s derogatory piece, wins sometimes, loses sometimes, and is the object of international hatred and protest. Her college wins, concurrent with the IOC’s new and open license for organizations to set their own standards of inclusion, appear to have led USA Swimming to make their requirements even more restrictive — reducing the acceptable testosterone level to 5 nmol/L, and requiring testosterone suppression therapy for 36 months prior to competition. However, attempts to enforce this new policy in the middle of Lia’s final season as a college athlete failed, and the NCAA allowed her to finish her 2022 season. This leads us to assume that Lia was able to pass the 10 nmol/L and 12 month benchmark that NCAA was then operating under.

This tracks with the experience of many transgender women who have access to hormone therapy: that they very much desire and do achieve testosterone suppression. Therefore, if most transgender women can easily pass the testosterone testing that the IOC originally inspired in 2015, then the question is essentially moot with regards to feminine transgender athletes. They can and should be allowed to compete as women. And indeed, they are: in 2021 Laurel Hubbard became the first, out transgender woman to compete in the Olympics in Tokyo. She didn’t win: she didn’t even complete any of her lifts in a qualifying way. But, she cheered for others and others cheered for her.

If Olympic-level transgender athletes can compete in the Summer and Winter games, then clearly there is no reason to exclude transgender teens from participating in school sports. No reason other than hate.


Mapping Attacks on LGBTQ Rights in U.S. State Legislatures – ACLU

The ACLU is tracking 220 Schools & Education bills in the U.S. – ACLU

IOC Consensus Meeting on Sex Reassignment and Hyperandrogenism November 2015 — IOC

IOC releases Framework on Fairness, Inclusion and Non-discrimination on the basis of gender identity and sex variations (2021) – IOC

Opinion – Celebrate trans athletes. But give cisgender women a fair shot at victory. – The Washington Post

Fairness for Transgender People in Sport – The Oxford Academic

Female excellence in rock climbing likely has an evolutionary origin – Current Research in Physiology

Nearly 1,000 contributors protest New York Times’ coverage of trans people – The Guardian
The testosterone rule—constructing fairness in professional sport – Journal of law and the biosciences

Red blood cells in sports: effects of exercise and training on oxygen supply by red blood cells – Frontiers in Physiology

Lia Thomas broke no records at the NCAA championships but left plenty of questions – The Washington Post

The IOC Has a New Trans-Inclusion Framework, but Is the Damage Already Done? – Sports Illsutrated

Transgender weightlifter Hubbard makes history at Olympics – AP News


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