The @dailymaverick asked me to do a piece on the trans woman in sport issue. It’s necessarily short and high level, but here it is. Writing it made me realize there are some key questions everyone who wades into the debate upfront should answer. Wanted to share them here (1/_)
The first question, before any other “shots are fired”, should be:

“If there is ZERO evidence for what happens to performance and/or biology in trans women undergoing treatment, what should happen for sport? Would you allow inclusion, or would you exclude until it exists?” (2/)
This is so important because it reveals a “value system” and understanding of women’s sport. If you believe in inclusion in the absence of evidence, you’re saying that women’s sport should be OPEN to self-ID, and then evidence must be provided to prove unfairness or risk. (3/)
On the other hand, if you say exclusion until evidence exists, you’re stating that women’s sport should remain CLOSED unless evidence can be provided to assure its participants that it is fair and safe to open it to athletes who have benefited from T during development (4/)
Once you’ve answered this first question, then you move to number 2, which is:

“The current policies for inclusion require suppression of T for 12 months, in order to allow participation without unfairness or harm. How strong is the evidence that this is actually achieved?” (5/)
Here’s where it gets as tricky as you want it to be, and you can act in bad faith to say “Ah, we are so helpless, there is no good research in athletes to answer this, we simply can’t say”. Which is why your answer to Q1 is important. However, such self-despairing pity is also...
...not even true, because there are some studies. In runners, there are 2 studies, neither particularly good. One finds that in 8 runners, with self reported times, spanning two decades, with no controls, no report of training, or even T levels, performance advantages are removed
The other showed that in DSD athletes who can use T, the suppression of T slowed performance by 5.7%, which is half the typical male advantage. So you could call it 1-1, but really neither study is very good. So then you find some good studies. (7/)
Those good studies are unfortunately not directly in athletes, but they are the ones that should really make sports organizations sit up and take notice. They show, without exception, that trans women who have suppressed T lose only small amounts of mass, muscle mass & strength
The result is a retained advantage over the correct reference group of females. The problem, of course, is that these comparisons are in non athletes, so both baseline and subsequent training induced changes are not directly assessed. But go back to Q1 now. Remember we said ZERO
...evidence, right? Well there’s NOT zero evidence. There’s actually a lot to suggest retained advantages, and when you look at published literature you find that training may make these even larger. How sport & scientists can ignore these is astonishing. It’s 12-0 on evidence
However, you may still hold that line, that there’s zero (or maybe you think insufficient) evidence, and so this inclusion should be the default. Which is fine, but that’s what should be stated upfront. Basically, you have to declare whether women’s sport is Closed or Open (11/)
Then you have to evaluate the “fix” - testosterone suppression. If you think it works to create fairness, safety AND inclusion, you’re ignoring a dozen studies that point in exactly the opposite direction. Now you have to treat women’s sport as open AND ignore evidence (12/)
All of which would make me wonder what the agenda is? Inclusion at the expense of all else? Ok cool, but then own it, and say “I think women’s sport should be open, despite available contradictory evidence with limitations, and I don’t care about fairness and safety of females”.
At least if you did that, it would frame subsequent disagreements, would be honest, and your position could earn some respect. But to pretend you’re holding up “scientific evidence” as a basis for inaction & then ignoring that which strongly suggests the fix doesn’t work? Come on
So if you believe in “open women’s sport to biological males until evidence shows we shouldn’t”, say so at the start, save us debate time. If you believe it should be closed, but also in inclusion, let me know which evidence you think supports this, I’d like to see it (13/13)

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More from @Scienceofsport

24 Oct
This is a sound and accurate logical explanation of why this notion of “matching for performance” to sidestep male and female sports categories is flawed. There are so many problems with it, one being that it fundamentally undermined the meaning of sporting competitions. (1/)
Another way to frame or conceptualise this is to recognize that if a female and male athlete are “matched” by this “unicorn-algorithm matching strategy”, the female athlete will be relatively better in their original category than the male athlete in theirs. Fundamentally unequal
A woman would be in say the 95th percentile for metrics like strength, speed, power etc, vs a men with equal numbers who is at around the 50th to 60th percentile for men. This “competition” enables relatively mediocre males to compete “equally” against excellent, top 5% females
Read 7 tweets
9 Oct
The World Rugby Transgender guideline is now out, and fully available here: You’ll also find a document called FAQs which tries to answer some common questions. We firmly believe it is the right thing in an emotive issue, for many reasons.
The Guideline is also accompanied by a visualisation that summarises the available physiological evidence that informed the Guideline. Here are those images, but I’d encourage consideration of all the issues - biological, legal, medical, social, ethical. All are in the doc & FAQs
As brief a summary as I can provide:
It is not possible to balance inclusion, safety and fairness. All the quality evidence, even if incomplete, strongly suggests that advantages are retained with welfare & performance implications. Therefore, players must compete in sex category
Read 10 tweets
9 Sep
Let me share a few thoughts on the latest #Semenya development - her appeal rejected by the Swiss Supreme court, World Athletics policy supported (pretty strongly too). We are planning a short pod on this tomorrow too, but here are a few thoughts… (1/…)
First, we’ve spoken a lot about transgender athletes recently. That has many elements to it. This has even more, and it’s really an unsolvable situation. It’s been present for nearly 100 years in sport, some horrendous attempts to manage it, and no clean solution in sight (2/…)
This decision establishes, for now, the policy that requires athletes with hyperandrogenism to lower T in order to compete. But not any hyperandrogenism, and not just any events. It covers only that caused by a selection of DSDs, where a person is 46XY, with testes, and thus (3/
Read 28 tweets
31 Aug
Last week, I posted a thread addressing a common criticism of transgender athlete policies, namely that they’re based on evidence in non-athletes. Here’s that thread, for a reminder. Today, I want to mull on another common issue raised in objection: (1/)
The objection is this: People argue that because trans women are often smaller, lighter, slower, weaker etc than biological females, it should be fine for them to compete as women. It’s an “overlap argument". Here’s one example of that thinking (this particular poll backfired): Image
The premise of the argument is this:
- Testosterone confers upon males advantages including size, strength, speed, power. This is why women have a separate category;
- If someone identifies as female (trans women), provided they’re not too big, strong, fast, they can compete as W
Read 15 tweets
24 Aug
This has been a common argument in the trans women in rugby debate. People have the idea that unless you *directly* study rugby AND show that TW cause injuries, it can’t be evidence based. Of course it can - there are peer reviewed studies that show two related things (thread)
2/ First, you have so many studies that identify both performance determinants and risk factors for injury in rugby. Dozens of studies identify when injury occurs, and thus what the significant risks for injury are. Similarly, performance is multifactorial but is KNOWN to be...
3/ …significantly influenced by a handful of testable/measurable factors. In fact, these measurable factors are so crucial and “robust" that teams actually have minimum standards for them, and select or drop players based on achieving these targets. They’re not “guesses”.
Read 22 tweets
24 Aug
@AntiAnja @Lukeyswords @cuthbert_shaw @JohnJMcGivern @WorldRugby We are hearing this argument a lot. People have the idea that unless you directly study rugby AND show that TW are causing more injuries, it can’t be evidence based. But of course, it can. Because there are peer reviewed studies that show two related things. First, you have...
@AntiAnja @Lukeyswords @cuthbert_shaw @JohnJMcGivern @WorldRugby …a ton of studies that identify what causes injury and performance in the sport. You know, based on hundreds of studies, when injuries happen, and how, and so you can identify the significant risks for injury and the determinants of performance. The performance variables are...
@AntiAnja @Lukeyswords @cuthbert_shaw @JohnJMcGivern @WorldRugby …so robust that teams actually have minimum standards for them, and select or drop players based on achieving these targets. Then second, you have a host of peer reviewed studies that have examined what the biological differences are between M and F, and what this means for
Read 12 tweets

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