Fond Of Women’s Sport: Dr. Emma Hilton & The Science That Shows Why Biological Sex Not Gender Choice Says Who Swims As Man Or Woman

2022-01-23 Reading Time: 13 minutes
Dr. Emma Hilton is fond of beetles - and safeguarding women's sport for biological women, too - image, Emma Hilton Twitter profile and various other beasts, airborne and aquatic (swimmer images, Adam Peaty and Ben Proud by Patrick B. Kraemer; Cate Campbell, courtesy of Swimming Australia; Bruno Fratus, Hannah Miley and Ranomi Kromowidjojo, courtesy of Arena)

Sunday Essay On July 10, 2019, Dr Emma Hilton, a prize-winning development biologist and research associate specialising in Cellular & Developmental Systems and well as Evolution, Systems and Genomics at the University of Manchester, was introduced to the audience at the Woman’s Place UK Conference with a short warm-up that included this on the impact that growing up as a boy and man has in sport:

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.

Kiri Tunks, founder and chair of Woman’s Place UK – image courtesy of Justice for Rohingya Minority

The topic of Dr. Hilton’s talk at a conference held in association with the campaigning group Fair Play for Women and also featuring British swimming ace Sharron Davies among speakers, was ‘review of the science supporting the IOC decision to let male-born transgender athletes into female competition’. None of the presentations went well for the IOC, starting early on in the video below, when the owner of the @FondOfBeetles Twitter account (some of her work has focussed on insects and the meaning of mutation in nature) confirms where she’s going:

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.”

Woman & Man in sport – Dr. Hilton’s presentation in full

Dr. Hilton first explained the basis of why a man competes among men and a woman competes among women in sport, focussing on the gap between the sexes when it comes to sports performance. The following are all precise quotes from her lecture in 2019:

  • 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.

Dr. Hilton notes that such a list is the tip of an iceberg of “6,500 differences in gene expression between males and females”, while “many unknowns” science has still to fathom.

She notes that “the majority of these differences are likely driven by testosterone-fuelled puberty – it is one hell of a drug”. It gave us Phelps and Bolt and, picking up on a theme this author has raised for the past three decades, “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”.

The transgender lobby, which has been successful in forcing societal change many agree with, has struggled to win some arguments, including that in sport that has resulted in desperate and often scathing and even abusive responses to statements and statistics such as those quoted above.

Not all transgender women agree with the transgender lobby when it comes to sport, however.

This Thursday past, the Arizona Senate Judiciary Committee passed SB1165 (dubbed “Save Women’s Sports Act,”), a bill sponsored by Sen. Nancy Barto, which prohibits transgender women from competing in K-12 and collegiate women’s sports, after heating compelling testimony from Jadis Argiope, a transgender woman who spoke in favour of the bill. Her testimony is well worth listening to:

Jadis Argiope emphasised two things: she is transgender woman and therefore “in no way” anti-transgender; and she wanted the committee to understand that sport should be categorised based on biological sex not gender choice. The few stats she was able to list before time ran out, speak to the journey Dr. Emma Hilton has travelled as a researcher and scientist who analyses research.

What It Means In Sport When A Man Identifies As A Woman

Dr Hilton described Transwomen as “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”.

She notes that her learning curve on the subject in regards to sport began in 2003, when the IOC formalised criteria by which Transgender women could compete in women’s sport after the following requirements had been met:

  • testes removal at least two years before competing;
  • legal status as female;
  • hormones in line with female profiles.

That was the new measure of fairness in women’s sport despite all that had been learned from the GDR’s systematic doping and the impact of androgenised girls, an impact that has to this day never been officially acknowledged by Olympic authorities in any way that would recognise abuse planned in the 1960s that is still affecting the lives of those who endured the Sporting `Crime of the 20th Century 50 years on.

The IOC based its criteria on “available information”. In 2019, Dr. Hilton described how she had set off in search of what that available information actually was and what it might say about the differences between men and women.

In her analysis, she told her audience: “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.

generic women swimmers dive

“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.”

Dr. Emma Hilton. Image courtesy of Patrick B. Kraemer

That told Dr. Hilton that the information available to the IOC in 2003 actually added up to this:

  • 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.

It was not until 2015 that the IOC updated its criteria, as follows:

  • surgical requirement scrapped
  • legal female status dropped in favour of a sworn declaration;
  • 12 months of ‘low testosterone’ required, set at a maximum threshold way exceeding typical female levels.

Before the end of 2015, there had been six more studies of bone density, confirming little to no change in skeletal structure when males transition, Dr. Hilton noted, adding: “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.”

Dr Emma Hilton – image courtesy of Patrick B. Kraemer

Dr Hilton summarised the journey up to 2014 by noting that up to that point “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”.

She added: “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.”

The “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” was not the worst of it. Dr Hilton noted that 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 …”. She believed that could politely be referred to as “ethically dubious”.

Even so, Harper’s study was embraced by the IOC as key guidance “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.”

The Evidence Since 2015

The research up to 2015 is still heading in the same direction, as the following graphic tweeted this week by Dr. Hilton, demonstrates *her full Twitter thread is linked to further down):

Since 2015, there have been eight published studies assessing aspects of transwomen physiology, Dr. Hilton told her audience in 2019, adding: “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.”

She then summed up what she had learned from all the papers she had read, leading her to conclude that there was nothing to support “the premise that transwomen can be fairly included in female sports”. In her words:

  • 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.
Swimming governance in focus – Photo by Patrick B. Kraemer

There is more data to come, Dr. Hilton noted: “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 decides to take any notice of such studies, and I can’t help but think that might depend on their results.”

The IOC had based its 2015 decision on politics (societal changes that did not take into account the nature of sport) not science, said Dr. Hilton.

She drew her presentation to a close saying: “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.”

In other words, should sport be a champion of ignoring the science that tells us what we know about biological sex and why that is wholly different to gender choice and identity. And should sport and those who govern and oversee sport, including the funding bodies and national governments, create an environment in which a focus on ‘elite’ sport, while leaving community sport a place where girls must compete with boys who identify as girls, among them some who have been encouraged to start sex-change processes before they are of a legal age considered appropriate to vote, to have sex, to be a part of what it means to be an adult?

Experience counts when it comes to what can happen – including the loss of confidence and the psychological and mental-health cost of being clobbered by rivals racing beyond the rules and principles of fairness – when sports authorities look the other way and fail to recognise the impact their wilful blindness has on generations of girls and women. Davies was on the stage at the conference that same day Here she is in conversation with Dr Nicola Williams of Fair Play for Women, the full transcript of the video below available here:

Dr Hilton concluded by noting that Louis Gooren, who first established that transwomen have significantly higher muscle mass than females, had told the IOC in 2004: “Depending on the levels of arbitrariness one wants to accept, it is justifiable that reassigned males compete with other women.” Says Dr. Hilton:

“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.”

Dr. Emma Hilton – image, courtesy of Patrick B. Kraemer

And so it has. In her latest tweets highlighting growing research findings, Dr. Hilton tweeted this thread:

In 2021, the IOC abdicated responsibility for setting transgender rules for Olympic sport. The buck was passed back to international federations, such as FINA in swimming, so that each of them can set their own rules, pertinent to circumstance.

It must be hoped, as FINA consider new rules that could be in place within a matter of months, that priority will be given to the science that leads practitioners and champions and many others to side with Dr. Hilton when she concludes that an open category for transgender athletes in sport is the place space should be created.

Among those who know what it’s like to race androgenised girls, let alone athletes who grew up from boys to men, are Sharron Davies, Michelle Ford, Wendy Boglioli and Nancy Hogshead-Makar.

Invading space is to be avoided if every girl in the world is not to believe that sport is void of Fair Play and the right to compete as a biological woman and is, instead, all about whether a man who identifies as a woman can race in the next lane with physical and other advantages (such as never having to worry about or be affected by menstruation when growing up) that women simply never have access to between the forceps, puberty and the stone, to borrow Joni Mitchell’s poetic description of a lifetime in Hejira.


The following will be updated with more links from time to time

The Science of Sport is among the best resources and includes the work of Professor Ross Tucker and veteran journalist Mike Tucker and their The Real Science of Sport Podcast“. The significance of sex not gender choice in sport transgender features in their rich vein and thread of topics, knowledgeable and robust discussions with expert guests, including Dr. Emma Hilton.

Some of the relevant episodes

Academic works

Transgender Women in the Female Category of Sport: Perspectives on Testosterone Suppression and Performance Advantage – Emma N. Hilton & Tommy R. Lundberg

Body Check: Reconciling Biology and Fairness while Supporting Trans Inclusion in Sport Emma Hilton,  Jon PikeLeslie Howe

Research covered by Mainstream media

By conflating gender and sex we undermine sporting competition

Latest official positions of note


Advocacy and media catching up with an issue that was only highlighted by Lia Thomas in the U.S. because neither swimming as a sport nor the media had noticed / cared enough to notice an issue live for many years

As 2022 Begins, A Major Schism Among Sports Gender Rights Advocates Is Brewing (ED: ‘brewing … lol!)

Fair Play For Women


Latest State of Swimming Coverage

Getting Into Trouble For Speaking Science On Sex – It Matters!

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