Transgender women in sport: Does ‘comparable’ mean ‘equal’?

Summary

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More or Less (BBC Radio 4):

"Transgender women in sport: Does ‘comparable’ mean ‘equal’?"
Date: March 14, 2026
Host: Charlotte MacDonald
Guests: Tom Coles, Professor Alan Williams, Dr. Bruno Gualano

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Episode Overview

This episode of More or Less examines the contentious debate over transgender women’s participation in women’s sports, focusing on a recent systematic review published in the British Journal of Sports Medicine. The hosts scrutinize what the review truly found concerning the physical fitness of transgender women versus cisgender women, question the strength of the data, discuss misunderstandings in the media, and explore what science can – and cannot – currently tell us about fairness in sporting competition.

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Key Discussion Points & Insights

1. Background: The Sex Divide in Sports

• Charlotte MacDonald opens by explaining how, aside from a few mixed events, the Winter Olympics demonstrated the norm of men and women competing separately, usually justified by clear physical differences such as speed, strength, and endurance.
  • (01:17) “Generally, in sport, that is what we consider fair because ... men are faster, more powerful and have greater endurance.”

2. The Study’s Headline: ‘Comparable’ Physical Fitness

• The episode discusses a new systematic review summarized in the media as showing that transgender women have no sporting advantage over cisgender women.

  • (02:19) The term “cisgender” is clarified as referring to women assigned female at birth.

• Tom Coles calls attention to the way the study’s findings were communicated:

  • (02:31) “‘Trans Women in Sport have no advantage over CIS women, study finds’ ... But is this what the study in question really found?”

3. What Did the Scientists Actually Measure?

• The featured research is a systematic review:

  • It collates existing studies comparing physical characteristics and fitness between transgender women and cisgender women.
  • Importantly, it did not conduct new physical tests.

• The review found that transgender women had somewhat more lean mass (muscle) but asserts that their overall “physical fitness” (a bundle of measures including strength and endurance) is “comparable” to cisgender women.

  • Professor Alan Williams points out that, generally, more muscle should correlate to more strength, so this conclusion is counterintuitive.
    • (04:10) “Alan says that that’s counterintuitive, as you’d expect people with more muscle to be stronger.”

4. Flawed Comparisons in Existing Studies

• The example of a Brazilian volleyball study is examined:

  • Only 7–8 participants per group; transgender women trained 4 hours/week, cisgender women 14 hours/week.
  • The transgender women’s group was also shorter, lighter, older, and competed at a lower level.

• Professor Alan Williams:

  • (05:48) “There’s a mountain of evidence that physical training affects these things... if one group is training more than three times more than the other group, we can safely assume that that is affecting the results.”

• Tom Coles underscores that these mismatches undermine meaningful comparison.

5. Statistical Significance vs. Real Differences

• The systematic review lumps together such studies; three out of four showed transgender women stronger, but none found a statistically significant difference.

  • However, the confidence in these findings was “very low” due to poor study quality and small group sizes.

• Charlotte MacDonald:

  • (07:03) “Saying they haven’t found a statistically significant difference isn’t the same as saying there’s no difference, especially when the controls aren’t in place to ensure you’re doing a fair comparison.”

6. Types of Studies: Cross-sectional vs. Longitudinal

• Most included studies were cross-sectional (snapshot at a single point), not tracking changes over time.

• Tom Coles notes what’s really needed are longitudinal studies following transgender women from the onset of hormone treatment to see real long-term physiological effects.

• There are “a handful” of such longitudinal studies, but these show only minor decreases in muscle and strength—or sometimes none at all.

  • Professor Alan Williams:
    • (07:56) “Small increases in body fat and a small reduction in muscle mass and a small reduction in muscle strength, or in several respects, there were no changes.”

• After three years, there wasn’t enough data to analyze absolute muscle mass, upper/lower-body strength, or endurance with confidence.

  • (08:08)

7. Scrutiny of the Conclusion: Is ‘Comparable’ the Right Word?

• So, why did the study describe the groups as ‘comparable’?
  • Professor Alan Williams:
    • (08:26) “My opinion is there are reasons why people haven’t done a systematic review like this before, and that is because there wasn’t a need for a systematic review of such poor evidence. To proceed with a systematic review and conclude then what they have, while partly acknowledging how poor the evidence is, but then be so clear in apparent conclusions is very strange.”

8. What Do the Study’s Authors Say?

• Tom Coles relays feedback from study co-author Dr. Bruno Gualano:

  • The term 'comparable' does not mean the two groups are “the same”; it means no statistically significant differences were found in the existing (imperfect) data.
  • He agrees that high-quality, well-controlled, long-term studies with trained athletes are needed and that their paper calls for exactly that.

• Tom Coles:

  • (08:57) “He says that this description of the groups being comparable should not be taken as meaning the two groups are the same. That interpretation is wrong. It’s rather describing the fact that the analysis did not find statistically significant differences between the groups.”
  • (09:55) “Our paper calls for exactly that” [well-controlled longitudinal studies].

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Notable Quotes & Memorable Moments

• Charlotte MacDonald on the complexity of the issue:
  • (07:03) “Saying they haven’t found a statistically significant difference isn’t the same as saying there’s no difference...”
• Professor Alan Williams on poor evidence:
  • (08:26) “To proceed with a systematic review and conclude then what they have, while partly acknowledging how poor the evidence is, but then be so clear in apparent conclusions is very strange.”
• Dr. Bruno Gualano (via Tom Coles), urging better research:
  • (08:57) “The analysis did not find statistically significant differences... but women well controlled longer term studies, especially in trained athletic populations, would be definitive.”

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Timestamps for Key Segments

• 01:17 – Introduction & framing the issue (sex differences in sport)
• 02:10–02:44 – Headlines vs. the study’s actual claims; systematic review explained
• 05:00–06:20 – Problems with study comparability (Brazil volleyball study)
• 07:00–07:40 – Statistical significance vs. real-world difference; need for better study design
• 07:44–08:20 – Limited longitudinal evidence
• 08:25–08:57 – Scrutiny of review’s conclusion; speaking with study authors

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Conclusion

The More or Less team concludes that the current evidence base for comparing the athletic capacity of transgender women and cisgender women is poor and limited. The systematic review in question provides no clear evidence that the groups are “equal” in sporting terms; rather, it simply did not detect statistically significant differences within the flawed and insufficient available studies. Both critics and the study’s authors agree: robust, long-term, and well-controlled research involving trained athletes is desperately needed to answer these questions more definitively.

Episode takeaway:
Media headlines may overstate or misrepresent the nuanced, limited findings of systematic reviews in this area. The debate cannot be settled until better, more precise and relevant data is produced.

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Transcript

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[Charlotte MacDonald]

Hello and thanks for downloading the More or Less podcast. With the program that looks at the numbers in the news, in life and in systematic reviews, I'm Charlotte MacDonald. The Winter Olympics finished a couple of weeks ago in Italy, and apart from a few mixed team events, for the most part men competed against men and women competed against women. Generally, in sport, that is what we consider fair because as the game showed, men are faster, more powerful and have greater endurance. But increasingly in sport, there's a controversy about transgender women, people who were born male and now identify as women. Is it fair for them to compete against women or do they have an advantage? A recent study in the British Journal of Sports Medicine has weighed into this debate. Here's the headline from their press release,

[Podcast Advertiser]

Physical Fitness of Transgender and Cisgender Women is Comparable. Current evidence suggests the study uses the

[Charlotte MacDonald]

term cisgender to differentiate women who were born female from transgender women who were born male. The study has been written up in online news stories with headlines like Trans

[Podcast Advertiser]

Women in Sport have no advantage over CIS women, study Finds.

[Charlotte MacDonald]

But is this what the study in question really found? Tom Coles has been looking into this one. Hi Tom.

[Tom Coles]

Hello.

[Charlotte MacDonald]

Let's start with the big picture here. The reason men and women don't compete against each other in sport is because that wouldn't be fair on account of physical Differences between the sexes, right?

[Tom Coles]

Yeah, that's right. So let me just introduce Professor Alan Williams, a sports scientist from Manchester Metropolitan University. And let's start with that thing you mentioned, the male advantage in sport.

[Professor Alan Williams]

There's a mountain of existing evidence before this paper appeared that says that there are differences between men and women in terms of their height and other skeletal dimensions, like limb length, in terms of their muscle mass and muscle strength, where, again, men have bigger muscles and stronger muscles.

[Tom Coles]

Now, transgender women are born male and then, as part of their transition, often undergo hormone therapy, among other things, this lowers their testosterone levels and leads to changes in their bodies, including other things being equal, a loss of muscle mass and strength. So the big question is whether the declines in muscle mass and strength are big enough to make it fair for transgender women to compete in the women's sport category.

[Charlotte MacDonald]

Okay. And so the scientific paper we're talking about today says that two groups are comparable. Some people have taken that as meaning that the changes in transgender women's bodies are big enough to mean the two groups are similar. Did the researchers involved go out and. And run tests on people to measure their strength and speed, for instance?

[Tom Coles]

No. No, they didn't. This paper is what's known as a systematic review. The researchers searched out all the scientific papers they could find comparing transgender men and women with other men and women in terms of their height and the amount of muscle and their fitness and strength levels. They then analyzed that in a bunch of different ways to try and draw out overall conclusions from all these different studies. In their summary of this process, they say that while transgender women had more lean mass, that basically means muscle than women. Their physical fitness was comparable. Fitness here is a general term covering upper and lower body strength and endurance. Alan says that that's counterintuitive, as you'd expect people with more muscle to be stronger.

[Charlotte MacDonald]

I mean, that does sound quite strange. Are we sure that the transgender women who are being tested are a good comparison with the women who are being tested?

[Tom Coles]

No, we're not. In some of the papers they use in this analysis, you can quite clearly see that they are definitely not comparing like with like. An extreme example is a paper from Brazil which compared the size and strength of transgender women volleyball players and women volleyball players. There were only seven or eight people in each comparison group, so it was quite a small study. Also, the amount of training done by both groups was quite striking. The transgender women did four hours training a week. The women group did 14 hours per week, over three times as much training as the transgender women.

[Professor Alan Williams]

Yeah.

[Charlotte MacDonald]

That doesn't sound like the comparison is fair.

[Tom Coles]

No. And Professor Alan Williams says training is really important.

[Professor Alan Williams]

There's a mountain of evidence that physical training affects these things. So, yes, if one group is training more than three times more than the other group, we can safely assume that that is affecting the results.

[Tom Coles]

The results in question found that the group of transgender women volleyball players were not as strong as the group of women volleyball players, which is not surprising at all. When you look at the two groups, the transgender women were shorter on average, weighed less and were older. They also played volleyball at a lower level compared to the women in the research who all played in national, not just regional, competitions.

[Charlotte MacDonald]

It doesn't sound to me like you should use a study like that to draw out wider conclusions on this question.

[Tom Coles]

It does seem odd, but that's the point of these systematic reviews. You look at a lot of studies and assess them in various ways to see what you can say. The volleyball study, for example, was used with three others in a comparison of upper body strength. The other three studies found that transgender women were stronger, but the analysis found the difference was not statistically significant. The researchers told me that was still the case when they removed the volleyball pa. At the same time, they also analysed the confidence you should have in this conclusion and found it to be very low.

[Charlotte MacDonald]

Right, but saying they haven't found a statistically significant difference isn't the same as saying there's no difference, especially when the controls aren't in place to ensure you're doing a fair comparison.

[Tom Coles]

No, the trouble with lots of these studies is that they're what's known as cross sectional. They're just comparing two groups at a single point in time. Without carefully controlling all the variables, you're likely to get some fairly meaningless results, which what you really want are longitudinal studies where you take a group of transgender women who are starting hormone treatment and measuring their muscle and strength over time to see if they change by enough to make them comparable to women.

[Charlotte MacDonald]

Yes, that sounds like the kind of studies you'd want. Do they have them?

[Tom Coles]

There are a handful of longitudinal studies included in the analysis, but they didn't show the scale of change in terms of loss of muscle and strength. You'd need to see either there were

[Professor Alan Williams]

small changes, such as a small increase in body fat and a small reduction in muscle mass and a small reduction in muscle strength, or in several respects, there were no changes.

[Tom Coles]

Looking at the effect of three years of hormone treatment, they did not have enough information to analyse absolute muscle mass, upper or lower body strength or endurance.

[Charlotte MacDonald]

So how after all that did they conclude that the strength and fitness of the two groups were comparable?

[Tom Coles]

That is the question.

[Professor Alan Williams]

My opinion is there are reasons why people haven't done a systematic review like this before, and that is because there wasn't a need for a systematic review of such poor evidence. To proceed with a systematic review and conclude then what they have, while partly acknowledging how poor the evidence is, but then be so clear in apparent conclusions is very strange.

[Charlotte MacDonald]

What do the authors of the paper say about this criticism?

[Tom Coles]

Well, I've been talking over email with one of the authors, Bruno Gualano, an associate professor at the School of Medicine of the University of Sao Paulo. He says that this description of the groups being comparable should not be taken as meaning the two groups are the same. That interpretation is wrong. It's rather describing the fact that the analysis did not find statistically significant differences between between the groups. He believes that despite all the problems with the studies they looked at, you would still expect large and robust intrinsic advantages to come through if they were there. Although he does accept the possibility that the weakness of the studies could have interfered with that. It's clear, he says, that after hormone treatment, transgender women do not have the physiological profiles of typical men. And he also told me women well controlled longer term studies, especially in trained athletic populations, would be definitive.

[Podcast Advertiser]

Our paper calls for exactly that.

[Charlotte MacDonald]

I think we can all agree on that one. Thanks Tom and thanks to Professors Alan Williams and Bruno Guarlano. That's all we've got time for this week. If you've seen a number in the news you think we should look at, email more or lessbc.co.uk. goodbye.

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