Dr Antonia Lee
Having listened to what seemed like another confused and confusing, rather irrational interpretation of the science of transgender sport participation from non-scientist and age-group (F35 — F44) cycling world champion, Rachel McKinnon, PhD, this time on the BBC’s Radio 4 (1), I would suggest that it really is time for journalists to do some research in order to facilitate evidence-based and informed debate on the topic. Here is a suggested simple framework that is perhaps more likely to aid constructive progress.
Complex intersex (DSD) conditions must be left out of the discussion
Rare and complex intersex (disorders of sexual development) conditions have no place in a debate regarding transgender sport participation. They have nothing whatsoever to do with any transgender argument and it is disingenuous in the extreme to conflate the two. In the interest of factual accuracy, intersex conditions are far rarer than McKinnon suggested. Fausto-Sterling (2) may have put the 2% (actually, 1.7%) of the population prevalence figure into some people’s minds, but her percentage included conditions that are not intersex at all. Applying a more precise, clinical definition, Sax (3) has suggested a prevalence of 0.018%. This has been discussed at length elsewhere (4).
The available testosterone research must be reviewed carefully and honestly
The study that was repeatedly cited by McKinnon in the BBC interview looked at endocrine profiles in 693 athletes in the post-competition setting (5). According to the authors, “the influence of sporting activity in endocrine physiology has become of increasing interest in recent years. The reasons include widespread abuse of hormones, particularly anabolic steroids (AS), erythropoietin (EPO) and human growth hormone (GH) as performance enhancing agents, knowledge that chronic over-training has potentially detrimental effects and the use of endocrine markers as a means of optimising training regimes”.
I suspect that even a non-scientist will read this and think, “Hmm. They are trying to look at endocrine physiology in a population that is known to do two things that alter this dramatically: 1) take performance enhancing drugs (PEDs); and 2) often chronically over-train”. These are massive confounding factors; acknowledged by the researchers in their discussion of the results.
The study data show the testosterone (T) overlap between the sexes that was mentioned and that appeared to be McKinnon’s only point: although no mention was made of those problematic confounding factors. Also missing was this and I’ll quote the authors directly, “in the case of the women, the arithmetic mean for serum testosterone of 2.68 nmol/l is nearly twice the mean of a non-athletic population but is heavily skewed by the high outliers. There were eleven female athletes with testosterone values above 8 nmol/l, three of whom had values between 25 and 35nmol/l.”
As the authors additionally comment, “(this)… would not exclude the likelihood of exogenous testosterone use, and it seems quite possible that one or more of them had the androgen insensitivity syndrome (AIS). The other women with intermediately raised testosterone levels may well have had the polycystic ovary syndrome (PCOS) or a more rare form of hyperandrogenism”.
Let me suggest a likely explanation for overlapping testosterone values between the sexes in elite sport. Male athletes who abuse anabolic steroids, or who chronically over-train, will often have low T. Female athletes who take exogenous T, or have PCOS, AIS or other conditions, will have high T. Group them all together haphazardly and there’s the overlap.
The authors’ own list of study limitations is long. They admit that they cannot rule out the possibility that any of the volunteers were doping. Let me here remind readers not involved in elite sport that other research has shown a prevalence of likely doping in 43.6% of elite athletes (6).
The authors of the endocrine study continue, “… a (research) weakness is that recruitment from sports was patchy and may not be truly representative, and there is no control group. Exercise can affect hormone levels and the lack of control for exercise and the lack of gender-specific reference data are further weaknesses of this study. Recruitment was by volunteering and some sports were not covered, and we were unable to recruit as many women as men. An analytical weakness is that T and other small molecules were measured by immunoassay which is not as accurate as modern mass spectrometry methods”.
It’s an interesting study that makes a valid point about the usefulness of an elite athlete biological/endocrine passport and that suggests further research. It’s not a study from which to draw the grand conclusions that McKinnon did and I am left amazed at this unscientific, illogical and out-of-context cherry-picking.
I could, for example, do exactly the same with another very recent (2019) study that simply asks, “Is testosterone responsible for athletic success in females?” (7), and quote the finding that, “T levels were positively correlated with athletic success in sprinters (runners, cyclists, kayakers, speed skaters, swimmers)”. To do so, however, and not to describe contextual detail, important aspects of methodology, obvious confounding factors, study limitations, peer-review (or lack of), or other possible explanations for the findings would be unscientific.
Two further studies that McKinnon didn’t cite are those of Eklund et al (2018) Serum androgen profile and physical performance in women Olympic athletes (8); and Handelsman et al (2018) Circulating testosterone as the hormonal basis of sex differences in athletic performance (9). Should you choose to read them you’ll know why.
I have highlighted elsewhere that Bermon and Garnier’s 2017 study (10), one that McKinnon has relied upon previously, has methodological flaws such that other scientists have asked for its retraction (11).
There are over 200 research papers referenced in the two papers of Eklund et al (8) and Handelsman et al (9). Add the 34 from the endocrine study of Healy et al (5), and that’s a considerable body of research from three papers alone that needs to be carefully considered; along with much more besides.
The effects of T during growth, puberty and maturation cannot be ignored
Testosterone during growth, puberty and maturation results in quite remarkable differences between the sexes. Testosterone in males at puberty drives: an increase in bone size and density; an increase in muscle size and strength; an increase in the tensile strength of ligaments and connective tissue; an increase in red blood cells… the list is extensive, with all of these changes, and others besides, resulting in considerable (10% plus) sports performance differences between males and females (12, 13). The fastest female sprinter in the world is easily beaten by male club athletes.
According to Handelsman et al (9), “Prior to puberty there is no sex difference in circulating testosterone concentrations and athletic performance. From male puberty onwards, the sex difference in athletic performance emerges as circulating testosterone concentrations rise as the testes produce 30 times more testosterone than before puberty, resulting in men having 15- to 20-fold greater circulating testosterone than children or women at any age. This wide, bimodal sex difference in circulating testosterone concentrations and the clear dose-response relationships between circulating testosterone and muscle mass and strength, as well as the haemoglobin level, largely account for the sex differences in athletic performance”.
The question that needs to be debated calmly here is this: “to what extent are these male-bodied, sex-derived performance advantages negated under current sport governing body rules for transgender athletes such that fair competition can take place?” There may be different answers to this question for different sports and events, bearing in mind the athlete’s age at transition and their previous sporting experience.
The myonuculei argument needs to be addressed
Muscle cells contain a number of nuclei — myonuclei — each responsible for their own section of the cell. With the right strength training programme, you can stimulate what are known as satellite cells to donate myonuclei to muscle cells. With more myonuclei, you get stronger, and can keep gaining strength (within reason and accepting confounding factors relating to health and ageing).
If you stop training, these donated myonuclei simply become dormant (14, 15). Contractile protein will be lost — the muscle will become smaller — but many of the myonuclei remain: for years. Then, should you start training again, they ‘wake up’. This largely explains why the person who has trained intensively, yet takes a break, invariably finds it doesn’t take long to get their strength back. The International Olympic Committee (IOC) appears not to have considered this important aspect of contemporary applied muscle physiology when arriving at its transgender guidelines. For fair competition, this needs urgent discussion. If a male-to-female transitioning athlete claims that they are, “genetically gifted at packing on muscle”, this is the likely explanation. It’s a cellular, male ‘muscle memory’ performance advantage.
The complexity of sport must be considered
In its revised 2016 guidelines regarding transgender participation, the IOC used some rather poor quality, qualitative data gathered from non-elite endurance athletes and appears to have relied more upon expert opinion rather than research, largely since there exists little in the way of good science at present (16, 17): a point subsequently acknowledged by two members of the IOC transgender panel (18). Endurance sports are quite different from sports where being big matters, or where performance is determined by maximum, absolute muscle strength or power. Combat sports also require careful consideration in the transgender debate. Let me again point out that in track-and-field athletics, men throw implements that are much heavier, and negotiate hurdles that are much higher, than the women do. A male-to-female, late-transitioning athlete would appear to have advantage upon advantage.
Solutions that don’t encroach on women’s spaces should be sought
I believe it is unfair in the extreme to expect women simply to move over and make way for male-to-female (MtF) transitioning athletes, with my position being informed by the overall, sex-derived MtF performance advantage described here and previously (19). In collegiate sport in the US and where sports scholarships are at stake, it seems especially unfair and discriminatory. Nobody is suggesting that transgender athletes shouldn’t compete or take part in sport. The eventual and fair solutions that hopefully will be arrived at should be those that don’t disadvantage others and that enable everyone to enjoy sport and compete fairly. Whilst my focus remains fair play in the women’s sport category, I will just note here that FtM athletes are allowed exogenous T under IOC rules. Since this could confer a performance advantage in certain cases, expect this performance opportunity to be exploited in elite sport.
Debate needs to be philosophical, evidence-based and rely upon critical thinking and reasoning
On the topic of transgender sport, I believe I’ve now seen a hay-wain full of straw men, piled high on top of a mountain of logical fallacies. The rhetoric and appeals to emotion have been overwhelming. Rather than all of this quite obfuscatory behaviour, it would be refreshing to hear clear explanations of contrasting positions based upon a calmly presented argument, with people being prepared to change their minds upon careful consideration of the available evidence and the quality and robustness of the argument presented. Abusive behaviours are additionally unhelpful.
2. Fausto-Sterling, A (2000) Gender politics and the construction of sexuality.
5. Healy, M.L. et al (2014) Endocrine profiles in 693 elite athletes in the post-competition setting. Clinical Endocrinology, 81, 294–305.
6. Ulrich, R. et al (2017) Doping in two elite athletics competitions assessed by randomised-response surveys. Sports Med; DOI 10.1007/s40279–017–0765–4
7. Ahmetov et al (2019) Is testosterone responsible for athletic success in female athletes? https://www.biorxiv.org/content/10.1101/557348v1
8. Eklund et al(2018) Serum androgen profile and physical performance in women Olympic athletes. https://bjsm.bmj.com/content/52/23/1531
9. Handelsman et al(2018) Circulating testosterone as the hormonal basis of sex differences in athletic performance.https://academic.oup.com/edrv/article/39/5/803/5052770
10. Bermon, S. and Garnier, P.Y. (2017) Serum androgen levels and their relation to performance in track and field: mass spectrometry results from 2127 observations in male and female elite athleteshttps://bjsm.bmj.com/content/51/17/1309
14. Gundersen, K. (2016) Muscle memory and a new cellular model for muscle hypertrophy and atrophy. http://jeb.biologists.org/content/219/2/235
15. Bruusgaard, J.C., et al (2010) Myonuclei acquired by overload exercise precede hypertrophy and are not lost on detraining https://www.pnas.org/content/107/34/15111