Transwomen vs females in sport: What does the science say?
Unfortunately, I need to start this post by clearly stating that I’m not transphobic. It’s actually rather baffling that this even needs to be said, but that’s the current state of affairs. So, I want to make clear from the get-go that I’m not ‘transphobic’ for writing about the scientific evidence surrounding athletic capabilities of transwomen.
The other thing I want to get out of the way is terminology:
- Male and female refer to the biological sex of a person.
- Men and women refer to the gender identify of a person.
- A transwoman is a male (biological sex) who identifies as a woman (gender identity).
- A transman is a female (biological sex) who identifies as a man (gender identity).
It’s nuanced, but it is important, especially as we dive into the research. My focus here will be on how the athletic performance of transwoman (males identifying as woman) compares to females even after gender-affirming therapy, which involves using exogenous hormones to become more like one’s gender identity.
In 2020, Roberts and colleagues published one of the most important studies investigating the impact of gender affirming therapies on athletic performance. They reviewed the records of 46 transwomen military personnel from the US Air Force and compared their physical performance results to the average for all females before, after 1–2 years, and after 2–2.5 years of gender-affirming therapy. The physical assessment included maximum pushups performed in one minute, maximum sit-ups performed in one minute, and the time to complete a 1.5 mile run.
First and foremost, the transwomen were an average of 11 kg (24 lbs) heavier than the females, a difference that remained throughout the 2.5 years of gender-affirming therapy, but were about 6.8 kg (15 lbs) lighter than the males. Thankfully, weight classes in sports take care of this difference.
For push-ups and sit-ups, performance differences disappeared after 2–2.5 years of gender-affirming therapy, but transwomen retained an advantage at the 1–2 year mark, able to perform 25% more pushups and 12% more sit-ups than females. For run times, transwomen were 8% faster after 1–2 years and 12% faster 2–2.5 years compared to females. I summarized this in the image below.
So, based on this study alone, we can say that performance advantages of being born male are retained for at least 2–2.5 years after gender-affirming therapy in transwomen, even if submaximal strength performance differences become insignificant. To give you an idea of how huge this 12% difference in endurance performance is, the difference between the fastest female’s 4 x 400-meter (1 mile in total) sprint and 25th place is about 2.1%. So, this difference would easily wipe the floor with females.
It’s also important to note that this study didn’t assess absolute strength (i.e., 1-rep-max) or explosive strength (e.g., throwing a punch). I was able to find a small study involving 11 transwomen that compared their isometric knee extension and flexion strength to females after one year of gender-affirming therapy, and it showed that strength was significantly higher both on an absolute basis and after adjusting for height differences.
We also have a handful of studies documenting greater handgrip strength in transwomen one year after gender-affirming therapy compared to females.
- In one study, handgrip strength remained around 40 kg, compared to the 75th percentile of females being just 31 kg. The authors note that all the transwomen were above the 95th percentile for females, despite starting below the 50th percentile for males.
- A second study found similar findings, with transwoman retaining grip strength of around 40 kg despite a year of gender-affirming therapy, which was way above the 31-kg average grip strength of the females.
- Lastly, a third study found that grip strength in transwomen after two years of gender-affirming therapy averaged 38 kg. While there weren’t any females to compare to, that’s still notably higher than the female averages from other studies.
So, it seems that what data we do have around muscular strength suggests that transwomen are notably stronger than females for at least a year after gender-affirming therapy, and likely for at least two years. And again, we don’t have any data around explosive power, which means we can’t draw reliable conclusions about the ability of transwomen to compete in female combat sports and related events.
Transwomen are faster and stronger than females for at least two years after gender-affirming therapy, which would give them a clear performance advantage in most (if not all) sports. It’s possible that these advantages disappear after longer periods of time, but we don’t have data investigating this hypothesis.
Transwomen have faced a lot of discrimination, so it is understandable that individuals want to try and make the world more inclusive towards them, sports included. I’m all for this in principle, but we need to go about it without discriminating against other groups of individuals along the way. It’s not fair for females to compete against transwomen that retain performance advantages from being male.
We certainly need more data to determine the point at which performance advantages disappear (assuming that they do), and until then, perhaps the best route of action is to simply create a trans-athlete league where transwomen can compete against other transwomen. That seems (to me, anyway) to be fair to everyone.