Trans women in sports: Is this fair?

[This is a transcript of the video embedded below. Some of the explanations may not make sense without the animations in the video.]

If you see a trans woman, like the American Swimmer Lia Thomas, in an athletic competition against women born female, it’s difficult not to ask whether that’s fair. In this video I want to look at what science says about this. How much of an advantage do men have over women and what, if anything, does hormone therapy change about it? That’s what we’ll talk about today.

The vast majority of humans can fairly easily be classified as either biologically male or female. The two sexes have rather obvious differences in inner and outer organs and those differences are strongly correlated with the expressions of the twenty-third chromosome pair, as you remember from your school days, XY for men, and XX for women. So far, so clear.

But this classification of the two biological sexes doesn’t always work. There is a surprisingly large variety of what’s known as “intersex” conditions in which the biological expression may be ambiguous or doesn’t align with the chromosome expression. Some cases are truly amazing.

For example, in 2014 researchers from India presented the case of a 70 year old man, father of four, who underwent surgery. The doctors discovered he also had a uterus and fallopian tubes. His chromosomes however turned out to be the standard male 46 XY.

Another example is the Spanish hurdler Martínez-Patiño who has feminine genitals but XY chromosomes and internal testes, something that she was herself unaware of until the age of 25. After this was discovered, she was banned from competing in the 1986 Olympics.

Such cases are called disorders of sex development, DSD for short. They are rare but not as rare as you may think. According to various estimates that you find in the literature they affect between one in a thousand and one in fifty.

This means that in the United States there are between about three hundred thousand and 7 million intersex people, and globally between 8 million and 160 million. Part of the problem with making those estimates is that the definition of an intersex condition is somewhat ambiguous.

Now, most intersex people aren’t transgender and most transgender people aren’t intersex, but the question what to do with intersex people in competitive sports is a precedent to the newer question of what to do with trans athletes. And Martínez-Patiño illustrates the difficulty.

Her condition is called hyperandrogenic 46XY DSD. In the general population, it happens at a rate of about 1 in 20 000 births. Women with this condition have elevated level of the male hormone testosterone. In 2014, a study by European researchers found that in elite female athletes the rate of this disorder is about 140 times higher than in the general population.

Testosterone helps muscles grow, strengthens bones, and increases levels of hemoglobin in the blood, which benefits oxygen transport. Synthetic forms of testosterone are often used for doping.

In case you think this pretty much settles the case that high testosterone levels are an unfair advantage for women, think again. Because the reason Martines-Patino was assigned female at birth to begin with is that she has what’s called complete androgen insensitivity syndrome. She has high levels of testosterone, yes, but her body doesn’t react to it. After being banned from the Olympics she appealed, arguing that she has no advantage from her elevated testosterone levels and the ban was indeed lifted.

However, there are other conditions that can lead to elevated testosterone levels in women. To make matters more complicated, there is a large natural variation in testosterone levels among both men and women and since women with naturally high testosterone levels tend to perform well in sports, they are overrepresented among athletes.

As a consequence, the testosterone distribution for male and female athletes has a big overlap. A paper published by researchers from Ireland and the UK in 2014 showed results of hormonal profiles of about 7 hundred elite athletes across 15 sports.

They found that 16.5% of men had low testosterone levels, 13.7% of women had high levels, and there was a significant overlap between the them.

So as you see, the business with the testosterone levels is much more difficult than you might think, and that doesn’t even touch the question how relevant it is. The advantages stemming from testosterone are particularly pronounced in disciplines that require upper body strength, and less pronounced in those that test endurance.

Having said that, let’s then talk about the trans athletes. Transgender people don’t identify with the sex they have been assigned at birth. Leaving aside the intersex conditions, this means a trans man was born biologically female and a trans woman was born biologically male. People-who-aren’t-trans are commonly referred to as cis.

Some trans people undergo surgery and/or hormone therapy to adjust their physical appearance to their gender. The results of the transition treatment differ dramatically depending on whether it’s started before or after puberty. During puberty, boys grow significantly more than girls and they develop more muscles whereas, to quote Meghan Trainor, women get all the right junk in all the right places. Physical changes during puberty are partly irreversible and transitioning later will not entirely undo them.

In 1990, a seminar convened by the World Athletics Federations recommended that any person who had undergone gender reassignment surgery before puberty should be accepted to participate under their new gender. This isn’t particularly controversial. The controversial bit is what to do with those who transition after puberty.

The International Olympic Committee has been leading the way on passing regulations. In 2004 they ruled that transgender athletes are allowed to compete two years after surgical anatomical changes have been completed and if they’ve undergone hormonal therapy. This means in particular that trans women must have taken hormone therapy for at least two years.

In 2021, the committee issued a framework that allows international federations to develop their own eligibility criteria for transgender and intersex athletes, so there’s no simple rule that applies to all disciplines.

But does the hormonal treatment make it fair for trans women to compete with cis women? 

In 2019 a team of European researchers from the Netherlands, Norway and Belgium measured the change in grip strength for trans people after a year of hormonal therapy. They had about 250 trans women and trans men each who participated in their study. So this isn’t a huge sample but decent.

They found that grip strength decreased in trans women by minus 1 point 8 kilogram but increased in trans men by 6 point 1 kilogram. In trans men, but not in trans women, the change in grip strength was associated with change in lean body mass. So it seems that hormonal therapy does more for trans men than for trans women.  

Another team of researchers from Sweden followed 11 untrained trans women and 12 untrained trans men before and up to one year after gender-affirming hormonal therapy.

They found that in trans women thigh muscle volume decreased by 5 percent and quadriceps cross-sectional area decreased by 4 percent, but muscle density remained unchanged and they roughly maintained their strength levels. In trans men, on the other hand, thigh muscle volume increased by 15 percent; quadriceps cross-sectional area also increased by 15 percent, muscle density increased by 6 percent, and they saw increased strength levels. Again it seems that hormonal therapy does more for trans men than for trans women.  

It’d be rather tedious to list all the papers, so let me just say that this finding has been reproduced numerous times. A meta analysis of from March last year surveyed two dozen studies and concluded that, even after 36 months of hormonal therapy, the values for strength, lean body mass and muscle area in trans women remained above those of cis women.

These numbers aren’t directly applicable to athletes because in the general population trans men have an incentive to build muscles while trans women have an incentive trying to lose it. But those studies pretty much agree that hormone therapy makes a faster difference for trans men than for trans women, and after 3 years the difference hasn’t entirely disappeared.

There is basically no data on what this hormone treatment does in the long run. A 2021 paper from Brazil suggests that after about 15 years differences between trans and cis women have basically disappeared. But this was a very small study with only 8 participants. And in any case, if you ask athletes to wait 15 years, they’ll be too old for the Olympics.

So let us come back to the question then whether it’s “fair” for trans women to compete with cis women. It seems clear from the data that trans women keep an advantage over cis women, even after several years of hormonal therapy. I guess that means it isn’t fair in the sense that no amount of training that cis women can do is going to make up for male puberty.

But then, athletic competition has never been fair in that sense. To begin with, let’s not forget that for athletic performance the most important factor isn’t your sex, it’s your age. And some people are born with an advantage at certain types of sports, being male is only one of them. Usain Bolt has long legs. Michael Phelps has big feet. And American Basketballers are tall.

Really tall. Here’s the American under16 Women’s Basketball team with the team from El Salvador. The Americans won 114-19. Is that fair?

And those are just the visible differences. There are also factors like bone density, cardiac output, or lung volume that are partly genetically determined. I never had a chance to become an Olympic swimmer. Is that fair? 

No. Athletes are biological extremes. “Fairness” has never been the point of these competitions. They’re really more like freak shows. Kind of like physics conferences.

There’s another aspect to consider, which is that these competitions should also entertain. I guess this is why the researcher Joanna Harper, who is a trans athlete herself, has suggested we talk about “meaningful competition” instead of “fair competition”.  We have historically segregated men and for women in sporting events because otherwise competition becomes too predictable, too boring. In some disciplines we have further categories for the same reason, like in weight lifting and boxing.

Now we’re asking if not we need additional categories for trans athletes. Alright, we could do this. But if you follow this logic to its conclusion then really the only person you can compete with is yourself.

Or you will have to try and measure every single parameter that contributes to athletic performance in a given discipline and then try to adjust for it. The result may be that the person who comes in last in a race is the winner, after you adjust for heart valve issues, testosterone levels, age, slightly misaligned legs, under average lung volume, and a number of other different conditions. And that would be “fair” in the sense that now everyone had chance to win provided they trained hard enough. But would people still watch it?

The question of entertainment brings up another issue. Most of the sport disciplines that are currently widely broadcast favor biological characteristics typically associated with men, with the possible exception of long distance swimming. But generally sex differences decrease the more emphasis a discipline puts on endurance rather than strength.

A 2019 study among casual athletes found that men still have an edge over women in marathns but somewhere between 100 and 200 miles, women begin to win out. Though this currently doesn’t reflect in the world records where men are still leading, it seems that men have less of an advance in endurance disciplines. Which brings up the question: Why don’t we see more of such sporting events? I don’t know for sure, but personally I find it hard to think of something more boring than watching someone run 200 miles. So maybe the solution is that we’ll just all just do esports in the end.

But let’s come back to the trans athletes. Researchers from the University of California estimated in 2017, that the percentage of transgender people in the United States is about 0 point four percent (0.39%). A similar estimate for Brazil put the number there at about 0 point seven percent(0.69%). If these number are roughly correct, transgender people are currently underrepresented in elite level sports. That isn’t fair either. This is why I think sporting associations are doing the right thing with putting forward regulations based on the best available scientific evidence, and as long as athletes comply with them, they shouldn’t have to shoulder accusations of unfair competition.

That said, professional sports associations will soon have a much bigger problem. Like that or not, genetic engineering has become reality. And as long as athletes can make a lot of money from having a genetic advantage, someone’s going to breed children who’ll bring in that money. This is why I suspect a century from now professional athletics will not exist anymore. It creates too many incentives for unethical behavior.

I hope this brief summary has helped you make sense of a somewhat confusing situation.