Myonuclei: the male-to-female sporting advantage

Dr Antonia Lee
7 min readJan 17, 2019

Dr Antonia Lee

A male ex-athlete in his 50s. After a few weeks of serious training, he was bench pressing over 140kg. Previously strength-trained males can regain strength rapidly, even as they age, thanks to the large number of myonuclei in their muscle cells. Dormant myonuclei represent a robust, cellular ‘male muscle memory’.

Much has been written about testosterone, sport, sex and gender. Indeed, quite recently I wrote a piece on the topic myself (1) pointing out that one repeatedly referenced study is flawed and that experts have asked for it to be retracted (2). The focus on testosterone and how it helps drive the major structural (anatomical) and functional (physiological) differences between males and females is entirely understandable (3). Less clear is how it affects sporting performance in transgender athletes. Since the concerns for those that care about these things seem to relate to humans born as male subsequently transitioning to identify as female and then going on to compete in women’s sporting competitions, that’s where I’ll focus my attention. Plus, I care about women’s sport.

Firstly, I think it’s important to look for good science (4, 5). This is more difficult than many people think. Non-scientists often find this hard to believe but doing good science with human participants is quite difficult. Ideally, a scientist wants to be able to be aware of all the possible confounding variables, account for these, and then by following the correct research methodology for the type of question being asked, be able to say that in a given population (or individual) the specific intervention ‘x’ results in the specific outcome ‘y’. Scientists are keen on causality. Even though I do less scientific research now and more coaching, I still like causal relationships. I like to know that when I design and implement a certain type of training programme, the likely outcome for the athlete in front of me is going to be what I intend it to be. Of course, this requires me to understand the athlete’s training response, which for a host of reasons, can be quite individual. So much so, that some physiologists talk of high- and low-responders to a given training stimulus (6).

It’s quite difficult to find good science when it comes to research regarding someone born a man who then transitions and competes in sport as a woman. One study by Joanna Harper usually crops up and it’s not very good (7). Harper managed to recruit just eight non-elite distance runners transitioning from male to female. Every piece of data appears to be self-reported by the runners. Essential information, including that regarding training history, injury, diet, weight, body composition, health (physical and mental) — in fact, all the things that influence the time someone might run for a given distance — is not provided. Given that the author is attempting to draw conclusions from events covering a time period of seven years and that seem to rely upon a runner’s memory and recall, this is poor. The research undertaken, as evidenced by just fifteen, narrow-focused references, is weak. The study reads more like an opinion piece reflective of the author’s bias as a male runner who transitioned to become female. Another, small-sample sized follow-up study is equally methodologically poor (8). Research guidelines exist for a reason and not to follow them renders that research quite meaningless (9, 10,11), of no benefit to society, and adds only to the mass of poor science on any topic (12). Harper sat on the International Olympic Committee (IOC) panel in 2015 that established the current transgender participation rules (13).

There exist — potentially at least — a number of what could be quite interesting observational single case studies. In other words, there are now quite visible humans (thanks to their efforts on social media) who were born male, now identify as female and compete in sport. It would represent significant progress and aid understanding were such individuals to offer to be research study participants. Naturally, an observational case study design with ‘n = 1’ can only provoke thought and provide insight regarding that one case in context, along with directions for future research; its findings cannot be applied generally. Unfortunately, the situation at present seems to be little more than hugely anecdotal: nothing has been measured, no longitudinal data exist, confounding factors have not been considered, whilst bias and emotional memories are creating meanings long after events and experiences. Meanwhile, lobbyists cherry-pick information according to an agenda. Anecdotes, tightly-coupled to bias and emotion, remain a good way of blinding people to science.

Science, by its very nature, is first and foremost about observation. The observation leads to an idea — the hypothesis — which can then be tested through an appropriate method of rigorous investigation. Much of my early interest and research in exercise physiology was in muscle adaptations to strength training. Since then, the field has developed and advanced; although I try and keep up-to-date. Let me now provide an observation regarding strength training and muscle adaptation, based upon both old (14), as well as more recent research (15, 16).

For a muscle to get stronger, it needs a specific stimulus. When someone first starts a well-designed strength training programme, gains — as measured by weight lifted for example — are rapid for the first three to four weeks. This is due to both inter- and intra-muscular co-ordination. What this means is that the athlete learns how to recruit the right muscles, in the right order. She also learns how to switch on, at the right time, the right number of muscle fibres (strictly speaking, the right number of motor units) for the given exercise and resistance to be overcome. It can be considered a phase of skill learning; or what I sometimes call ‘training the nervous system’.

Gains — still measured roughly in terms of weight lifted — subsequently slow down. Physiologically, what now needs to happen is that the training programme needs to cause changes within the muscle fibres (cells) themselves. Muscle cells contain a number of nuclei — myonuclei — each responsible for their own section of the cell; their domain. With the right strength training programme, you can stimulate what are known as satellite cells to donate myonuclei to muscle cells. With more myonuclei, along with other physiological adaptations — such as an increase in contractile proteins — you get stronger; and with the right programme, can continue gaining strength year after year, within reason.

Now here’s the interesting point. If you stop training, it seems that these donated myonuclei simply become dormant. 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.

That’s my scientific observation backed both by research and forty years of training athletes, male and female. Now, a few more facts. What factors can drive muscle cells to end up with more myonuclei? Testosterone during growth, development and maturation; appropriate strength training; and anabolic steroids (15, 16).

Now for a little thought experiment that might lead a scientist or two to engage in useful research. Let’s imagine I’m a man who trains or competes in sport, even at a modest performance level. Well into my 20s, perhaps even into my 30s, I make the big and challenging decision to transition. I follow the IOC rules and take the appropriate hormone treatment such that my testosterone levels fall below the designated limit and I can legally compete against women. Even if I haven’t trained for twelve months or more, I’ve still got all those extra, dormant myonuclei from my physiological development as a man, and even more from being a man who has trained previously. It will be much, much easier for me to become stronger and more powerful than if I’d been born a woman. This permanently higher number of myonuclei may be regarded as a form of robust, cellular ‘male muscle memory’ and it represents a potentially massive transgender advantage in certain sports. The sporting world desperately needs new, good science to clarify this matter.

The IOC and other sport governing bodies need to think far more deeply, critically and scientifically about the transgender issue than they have done so far. At the very least, the IOC needs to listen to other, well-informed voices and consider commissioning studies that look at muscle physiology and strength adaptations pre- and post-transition. As it stands, it would be easy to reach the conclusion, based upon current muscle physiology research, that a physically big man involved in sport, should he decide to transition, has a significant and unfair advantage over women in sports, events and disciplines where size, muscle strength and muscle power largely determine the performance outcome.





4. Heneghan, C. et al (2012) Forty years of sport performance research and little insight gained. British Journal of Sports Medicine [online]. Available from <doi:10.1136/bmj.e4797>

5. Young, S.S. and Karr, A. (2011) Deming, data and observational studies. Significance(The Royal Statistical Society). September, pp. 116–120.

6. Bouchard, C. (2012) Genomic predictors of trainability. Experimental Physiology, 97 (3), pp. 347–352.

7. Harper, J. (2015) Race times for transgender athletes. Journal of Sporting Cultures and Identities. Volume 6 (1), pp. 1–9.







14. Rutherford, O. and Jones, D.A. (1986) The role of learning and co-ordination in strength training. European journal of applied physiology and occupational physiology. 55 (1) pp.100–105.

15. Gundersen, K. (2016) Muscle memory and a new cellular model for muscle hypertrophy and atrophy.

16. Bruusgaard, J.C., et al (2010) Myonuclei acquired by overload exercise precede hypertrophy and are not lost on detraining



Dr Antonia Lee

An elite coach with degrees in science and sports medicine.