Tweeting as @FondOfBeetles, developmental biologist Dr Emma Hilton has helped many of us understand the science behind the differences between the male and female sex and how that translates to sporting performance.
Sport is meaningless without fair competition. Some people say that if a man transitions into a woman this eliminates all the male performance advantage they had as a man. Science does not support that claim. Male puberty locks in many changes to the male body that simply cannot be reversed.
This is the video and transcript of the speech given by Dr Emma Hilton at the #WPUKFairPlay meeting in London on 10th July.
Hello everyone. Wonderful to have the chance to speak here tonight. I’ll try not to be too much of a science bore, but I can’t promise anything.
That males as a class are stronger than females as a class is not controversial, and I’m not going to provide any references for that statement. To quote Ani O’Brien:
“Pretending that this isn’t something we have known as a species since the beginning of our collective consciousness is ridiculous.”
Reproductive anatomy aside, the physical differences between males and females were already apparent when our ancestors emerged from the trees, and now, in modern sports, we can measure them precisely. Males can run faster, jump longer, throw further and lift heavier than females. They outperform females by 10% on the running track to 30% when throwing various balls.
- So big is the gap, there are 9000 males between 100m world record holders Usain Bolt and FloJo.
- So early does the gap emerge, the current female 100m Olympic champion, Elaine Thompson, is slower than the 14 year old schoolboy record holder.
- So unassailable the gap has proven to be, virtually all elite sports have a protected female category, to allow females to compete fairly against those with the same female potential, and to win, and, OK, to make a little money maybe.
Boys and girls diverge physically early on in life, at 7 weeks gestation to be somewhat more precise, when genetic makeup drives sex differentiation into male or female forms, and the dimorphic characteristics associated with sex begin to develop. At birth, boys are, on average, taller, heavier and they have, of course, bigger heads. In childhood, they can plank for a longer time, do more pull-ups, run faster. But the differences are not huge, mixed sport prevails in little schools across the world, even though boys never learn to pass the football to girls.
Male puberty is the point at which boys really open the physical gap on girls. To 10 years old, testosterone levels in boys and girls are broadly similar. At puberty, male testosterone levels surge and stabilise at around 20 times higher than in females. This surge shapes a boy into a man, and into a superior athlete.
Males are five inches taller than females. Longer arms give a greater reach and can generate more speed on a cricket ball. Bigger hand spans can more easily palm basketballs. Longer legs and narrower pelvises lead to better running gaits. Males need fewer strides to cross a distance and the strides they take are more efficient.
Males have around 40% more muscle mass, even when height is taken into account, and 40% less body fat. The muscle they have is denser, more fibres, larger fibres. Higher numbers of muscle stem cells make new muscle fibres, donate nuclei to strengthen existing muscle fibres, help healing. They have higher proportions of fast twitch fibres – these are the fibres responsible for explosive movement. Stiffer connective tissue – ligaments and tendons are tighter springs – means greater storage of potential energy and even more explosive power. In short, male muscles can move way more quickly and with far greater force than female muscles. And with larger hearts, lungs and haemoglobin pools, they can feed them more oxygen.
This list, now deeply familiar, is nowhere near comprehensive, and with 6500 differences in gene expression between males and females, there are still many unknowns. The majority of these differences are likely driven by testosterone-fuelled puberty – it is one hell of a drug. It has delivered us athletes like Usain Bolt and Michael Phelps. As the original anabolic steroid, used widely in the 1980s in state-led doping programmes, it has almost certainly delivered us a fair few elite females too.
Transwomen are, for the most part, physically healthy males who experience a feminine gender identity and who may take social and medical steps to be perceived as female. In 2003, the IOC formalised criteria by which these physically healthy males who experience a feminine gender identity may compete in female sports. These criteria were:
- testes removal at least two years before competing;
- legal status as female;
- hormones in line with female profiles.
These measures, the IOC decided, were sufficient to ensure fair competition between females and transwomen.
Writing after the 2003 decision, sports physician Jonathan Reeser stated:
“It is not hyperbole to state that the IOC took a bold step when it decided to permit the participation of transgender athletes in the Olympic Games. Experience will eventually tell us whether they made the correct decision, and whether the modern female athletic playing field will remain level. Until such time when we can reflect on that experience with perfect hindsight, we must make the best decisions we can with the information available.”
I repeat: The best decisions with the information available.
So, I tried to find out what information was, and is, available.
I searched medical databases for studies of transwomen and any performance-relevant changes they may undergo with hormonal and/or surgical transition. In 2003, the published information available to the IOC was somewhat sparse. It consisted of just five studies on bone density covering around 120 transwomen up to 3 and a half years after gonadectomy. None detected any significant or enduring difference in bone density compared with reference males. That’s it.
However, in 2004, one of the experts present at the 2003 meeting published, for the first time, data on muscle changes in transwomen, and the study length of three years and the title – “Transsexuals and competitive sport” – indicates this data was presented ahead of publication at that 2003 meeting. Louis Gooren had studied changes in muscle area in 19 non-athletic transwomen and shown that after three years of hormone treatment, muscle area in transwomen decreased but remained significantly higher than in control females. Gooren also noted that the height of his cohort did not change.
So, in 2003, the information available to the IOC was:
- males are stronger than females;
- males out compete females in sports;
- transwomen do not lose bone mass nor magically get shorter;
- even three years into transition, transwomen retain significantly larger muscle area compared with females.
Based on this, the 2003 decision by the IOC to declare it somehow fair that transwomen compete in female sports seems, well, rather illogical. Some may say unscientific.
The IOC updated their criteria for inclusion of transwomen in female sports in late 2015:
- jettisoning the surgical requirement;
- swapping legal female status for a sworn declaration;
- and requiring 12 months of ‘low testosterone’ at a maximum threshold way exceeding typical female levels.
OK. Maybe they jumped the scientific gun in 2003 but, in the intervening 12 years, were proven correct, perhaps even a little conservative, hence the reduced stringency? Well, not exactly.
Following Gooren in 2004 and before late 2015, there were six more studies of bone density, confirming little to no change in skeletal structure when males transition.
In 2007, a second study containing muscle data was published, albeit by the imperfect marker of lean body mass. This study showed that after 12 months of estrogen, transwomen remained the same height, they lost a little lean body mass, and gained a little body fat. The % changes were tiny. Interestingly, just with estrogen, final testosterone levels were well below the IOC threshold.
Then, two studies reporting actual performance outcomes were published by the same research group. The first in 2008 studied 23 non-athletic transwomen, all at least 5 years into transition including gonadectomy, and the second, in 2015, tracked 44 non-athletic transwomen from pre-transition to two years of hormone treatment. Compared to reference males, transwomen had lower muscle mass and more body fat, and were weaker across measurements of grip strength, bicep strength and quad strength.
The authors of these two studies, and perhaps the IOC, were concerned with how much weaker these transwomen were compared to males. I calculated how they compared to females. Well, they’re still stronger, a lot stronger, especially in the upper body.
So, up to 2015, the body of information available to the IOC comprised four studies showing that transwomen even five years past transition and their testes long gone retain more muscle mass and remain much stronger than reference females. There was someone at the 2015 meeting who argued a rather different picture though. That person was Joanna Harper, a transwoman and distance runner, and she published her findings in 2015 – month unknown – in a paper that I find difficult to discuss sensibly. And with a straight face.
Harper studied eight sub-elite runners, pre- and post-transition, and graded their performance for age and sex. There are many, many flaws in this study. Firstly, the data is hardly more than a collection of anecdotes, with the majority of times self-reported, not verified, and reliant on memories often spanning decades. I can’t even remember my run times from a month ago. She may as well have surveyed Twitter, although that would have had lots of people offering their compromised performances with pickle jar lids rather than 10k races.
So, small cohort, no control group, transition times varying from 1 year to a whopping 29 years, no correction for the myriad changes any athlete may experience regarding fitness, diet, training regime, injury. Causing me the most concern, and I’m not sure it’s widely known, Harper’s study was published by a sports society where authors pay to submit manuscripts and agree, in return, to review those of others, each of whom has paid to submit a manuscript…and so on. Politely, this could be referred to as ethically dubious.
Yet Harper’s study, as poor as it was, and even containing examples of transwomen with vastly improved running performances after transition – one moved from the 55th to the 75th percentile – it is widely understood to have been key in persuading the IOC to make it easier for transwomen to enter female sports, despite the increasingly consistent evidence out there that transwomen long after transition remain more muscular and stronger than females.
Since 2015, there have been eight published studies assessing aspects of transwomen physiology. Two focused solely on bone health. Four confirmed previously-observed data on body composition. That is, transwomen gain a fair bit of body fat and lose a small amount of lean body mass.
The final two, both published last year, tracked the effects of transition in around 100 males before or shortly into puberty, to around 20 years of age. Males as young as 12 were treated with puberty blockers, followed by hormone treatment at 16 years old, with some opting for gonadectomy after 18 years of age. Attained height was male-typical. Body fat was female-typical. Lean body mass and grip strength was lower than in reference males and in males transitioning as adults, but still, despite the early intervention, remained far higher than in age-matched reference females.
And there ends the literature review.
- Of the papers returned in my systematic search, only 11 contained any data most relevant to sporting performance.
- Only 4 of these contained any direct measurements of performance.
- Only 3 of these were good science.
- Only 2 of these were available to the IOC in 2015, both of which demonstrate that transwomen retain far superior muscular architecture and strength that would favour competitive advantage, and neither of which supports the premise that transwomen can be fairly included in female sports.
There are two studies in progress that may provide excellent data, one in Sweden and one in the UK, that will – between them – assess muscle changes like fibre size and fast twitch proportion, and measure performance outcomes such as strength and aerobic capacity in athletes. I welcome such studies, although it’s going to take years before the data is compiled, analysed and used to inform sporting policies. That is, of course, if the IOC decide to take any notice of such studies, and I can’t help but think that might depend on their results.
One attendee at the 2015 meeting, Arne Ljungqvist, wrote:
“It has become much more of a social issue than in the past. It is an adaptation to a human rights issue.”
Other attendees, including Harper herself, have stated:
“There is now an urgent need to determine not only what physical advantages transgender women carry after HRT but also what effect these advantages may have on transgender women competing against cisgender women in a variety of different sports.”
You’ve kind of undermined your own study there, Joanna.
These are open acknowledgements that the 2015 IOC decision was political, was not based on valid scientific evidence, and that fair competition for females was not a primary concern. Remember this the next time someone asserts that the IOC policy is based on the best medical and scientific information available.
The IOC initially predicted that, as only 1 in 12000 males has gender dysphoria, the number of transitioned males wishing to compete as females would be negligible. In 2005, Arne Ljungqvist and Myron Genel, both IOC committee members, wrote:
“Inevitably there will be transgendered athletes, such as Renee Richards, who will be competitive at a high level, but most will probably wish to compete only at a Masters level or at local and regional events.”
In an increasingly gender-fluid society, the reduced stringency to meet female competitive standards may see more than a negligible number of males competing in female sports. Regardless, I suspect that Sharron Davies may disagree with the idea that just one competitor with an unfair advantage should be so easily dismissed as harmless. The females competing against Rachel McKinnon will argue that fair participation, even in Masters level sport, is not disposable. The schoolgirls competing against Terri Miller for college scholarships may feel that fair competition in local and amateur sports is somewhat important.
Louis Gooren – he who first established that transwomen have significantly higher muscle mass than females – had, in 2004, the following advice for the IOC:
“Depending on the levels of arbitrariness one wants to accept, it is justifiable that reassigned males compete with other women.”
I go back to this recommendation a lot, and I still can’t believe that the first formal attack on female sport was so openly acknowledged as arbitrary. Sex segregation in sports does not exist for arbitrary reasons and it should never have been compromised for arbitrary reasons.
The IOC and other sports federations are pursuing a social principle, and female athletes are considered collateral damage.
We must continue to fight this.