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
This leads the argument that trans women inclusion should be dealt with on a case by case basis. If you measure & limit enough variables, problem solved! Right?
Well, no, and I just want to think out loud about some issues. Here’s an example of the actions it calls for (4/) Image
So, first, let’s begin by recognising that there IS overlap between M & F in pretty much every variable we can think of associated with sport. Many women are faster, stronger, heavier, taller than many men. This is obvious. How many of you men are faster than Radcliffe? Yep (/5)
We can (and have) quantified this for mass in rugby, for example. See figure below - the typical male is slightly heavier than the 99th percentile for females (the heaviest 1% of women almost as heavy as typical males). So there is clearly overlap in each attribute, independently Image
The argument now is that some trans athletes, those who overlap and are lighter than males, should be included because if mass is the problem, they create no problem. Except…couple of things. First, mass is not the only thing that matters. It’s one of many attributes that drive
…performance and safety risk. Even at the same mass, evidence is compelling that men are stronger than women. In fact, to match strength, you often need a male who is 20% to 30% lighter than a female. So simply focusing on mass misses many of the factors for safety & performance
But more to the point, where do you set a threshold? Should it be 75kg? 90kg? 60kg? No matter where you set it, the group of humans who fall just under it, AND who have strength & speed advantages would all be male. So this idea of ‘limits’ is a shortcut to ‘no women in sport'
Second, it’s a misunderstanding of why categories exist. Do you allow a 27 year old adult to play against 17 year old children if they’re “a bit smaller than average and not that strong”? Would you allow a weak heavyweight to fight middleweights just because they lack strength?
In other words, why make an exception that allows someone to cross into a protected category just because that person lacks the attributes that category is associated with? The sexes are divided by sex, not weight/strength etc, even though they may be correlated with it.
Next, a philosophical question - if sport is to set up some kind of ‘bright line test’ to decide which applicants for women’s sport should be allowed in and which should not, how does one draw that line? Is sport going to decide who is “womanly enough” for sporting purposes?
On what basis might sport decide that person A cannot play women’s sport, but person B can? Some complex algorithm that factors in all the relevant attributes? Think of how that would be tested. It’s more discriminatory than ever, and lacks rigor and integrity. I can’t see how
…sport can be tasked with running that test. It would also have to be ‘cheat proof’ (look at paralympic classification for why), done regularly, and it would need to be absolutely accurate, or it would not address the risk issues anyway. I don’t know what these tests look like?
In short, the “overlap” argument seems to me to argue for a new way to categorise people for sport, and it’s one that would end women’s participation in sport, because wherever you draw a bright line, biological males will have performance advantages in other attributes around it

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More from @Scienceofsport

Nov 16, 2022
Let's talk about foul play, red cards and head injuries in #Rugby Here's a thread on head injury risks and the 'levers of control' to try to reduce it, with some background and some data... 1/
Back in 2017, when we first analysed risk factors for head injury, it was clear that higher tackles increased risk. This is pretty obvious - the only way a ball carrier can be injured is from a high tackle, and we also found head-to-head contact was most dangerous for TACKLERS
This was the trigger or catalyst for a clampdown on high tackles. This would DIRECTLY protect the ball carrier, but harsher sanctions, applied more frequently, would carry a MESSAGE to tacklers to target lower, and avoid those highest risk head contact situations
Read 15 tweets
Jul 29, 2022
This thread typifies two broad approaches to this issue. On one side are people whose paradigm is "There's no evidence (according to them), so there's no reason to prevent males from entering women's rugby". On the other is a group who say "Male physiology is very different from
...female physiology because of androgens and male development, so we need to prevent males in women's rugby until the evidence strongly suggests it is fair and safe". The latter group is not without evidence, mind. We know the initial typical M vs F differences, and we know the to which biological attributes ranging from skeleton to muscle mass/volume & muscle strength change. So we do have evidence of retention of male biology and thus advantage and safety risk (contrary to what that thread suggests). But the former argument - allow it until
Read 13 tweets
Jul 15, 2022
Another example is cars vs motorbikes, which is more dangerous? If you only count road accidents/deaths, you'd conclude that cars are more dangerous. And you'd be wrong, because you've failed to account for 'exposure'. Now let's think rugby....
If you watch rugby, you will see many more head-hip proximity tackles than you see head-head proximity tackles. Hips are "selfies or cars", & heads are "sharks or motorbikes". We can quantify this, and it's 2.6 head-hip tackles (18%) for every 1 head-head tackle (7% of tackles).
Similarly, you'll see a lot more bent tacklers than upright tacklers. The ratio here is 2.2. 57% of tackles are by bent players compared to 26% by upright players. So it's not *that* surprising that you see bent, head-hip injuries - the event is common (like cars & selfies)
Read 8 tweets
Jul 15, 2022
Rugby and HIA risk (thread):
Ahead of a big rugby weekend, thought I'd offer a little insight into when the risk of head injuries is highest, and how World Rugby has tried to nudge behaviour towards safety (the Red and Yellow cards you see, that is). So here's a little tutorial!
First, and sorry for the wordy slide, but we need to understand how risk reduction works in the global sense. To simplify, you're either eliminating, substituting, or modifying what is risky. To do this, you have to first understand a spectrum of risk. That is, "what is risky?"
Here's another slide (fewer words) that illustrates that, shows the spectrum of risk idea, and also introduces the idea of modifying a behaviour to lower overall risk. This concept underpins what happens next, which is the data part of the process. (3/
Read 29 tweets
Jun 28, 2022
Upon further reading, the following strikes me. Based on the science (without quotation marks), in sport, where SEX DOES matter, there *IS* a choice to be made, the reality that fairness & safety for women can’t co-exist when male advantage is retained...…
Is that choice easy? No. So the headline is immediately misleading. The choices create consequences. But they’re consequences in a colliding rights issue, so if you only ever consider them from one POV, you can’t do justice to the difficulty of those choices. That’s THE problem
Whether you choose inclusion of TW into W’s sport, or whether you choose like World Rugby and FINA, you create outcomes for BOTH sides of this issue. @jonathanliew’s piece argues for only one group’s claims. Women would, I suspect, have strong views of their own. But what the
Read 12 tweets
Jun 28, 2022
Jon’s thread below is good, and I agree. My first impression of this article was a bit simpler. I thought the quotation marks around “fairness” and “the science” were doing a comically large amount of work, but also quite revealing of the line of reasoning about to follow!
Then comes the second part, where I assume based on a lack of quotation marks, that we are now talking about real science. This is the sociological equivalent of “but Michael Phelps’ arms”, with a seasoning of blackmail. I’d answer the Qs at the end with: “please do & irrelevant”
What that boils down to is that we should side-step what we know are reasons for the women’s sport category, and create a kind of general ledger method of exempting people for sociological disadvantage. I would absolutely love to see the numbers run on this.
Read 4 tweets

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