Why a Case-By-Case Approach to Transwomen’s Participation in Female Sports Won’t Work

A scientific demonstration by Greg Brown

Maybe you, like me, are feeling lots of different feels right now—elation over the very sane sounding Executive Order, suspicion over how easy that was (if something seems too good to be true…), discomfort with the fact that sports and locker rooms are not addressed specifically. On the one hand, it’s like manna from heaven to hear the federal government say it’s wrong to deny biology and use coercive means to wedge men into women’s spaces. This sentence is so true, so painfully, obviously weepingly true: “The erasure of sex in language and policy has a corrosive impact not just on women but on the validity of the entire American system.” There’s a strong hallelujah, sell my clothes vibe.

On the other hand, Pritzker. Gill. Rothblatt. The ACLU. Eddie Ruter. An Executive Order can be legally challenged, and it definitely will be. Twenty-four states adopted Biden’s redefinition of sex as gender identity, so sports participation in schools and colleges in almost half the country is still based on gender identity. Lawyer types should correct me if I’m wrong, but in those states, it’s still up to girls to sue the state for their right to single sex sports. That’s an enormous financial and time cost that few can afford. And of course, an executive order can be reversed with the stroke of a pen. Our troubles are not over. Don’t sell your clothes.

The Executive Order was a big step toward restoring women’s rights, but we’ve got to keep walking, even running. In the name of exposing falsehoods, forward momentum, and putting biologically true statements out in the universe (hiya, hippie mofos), Greg Brown offers a detailed demonstration entitled Why a Case-By-Case Approach to Transwomen’s Participation in Female Sports Won’t Work.

Brown is professor of exercise science in the Physical Activity and Wellness Laboratory of the Department of Kinesiology and Sport Sciences at the University of Nebraska Kearney. He has written scholarly papers, and expert reports for legal cases, affirming the biological differences between males and females, the impact of those differences on sports performance, and the importance of keeping males out of the female sports category.

In November 2021, the International Olympic Committee (IOC) published the trippingly titled Framework on Fairness, Inclusion, and Non-Discrimination on the Basis of Gender Identity and Sex Variations. By any scientific measure, it was a piece of work. To even make a gesture of fairness, the IOC was forced to declare that transwomen, i.e. males, should have “no presumption of advantage” over women. Male, female, the same. Even the IOC felt the need to caveat an absurdity like that. Okay…mumble mumble…meaningful competition…mumble mumble…disproportionate advantage…and case-by-case assessment has been suggested as a possible solution! Here’s the idea behind case-by-case assessment. You know how in a marathon, for example, the elite women will go by, each one 100 pounds of World Championship kick ass, and about two hours later some dudes will totter past, a festival of fallen arches and pizza pockets. The IOC saw this, and said, See? Some men have no advantage over women. And case-by-case eligibility has been casually tossed out as a solution to inclusion of men in the female category by sports organizations and people who identify as scientists with tiresome regularity. BUT THEY NEVER GET INTO THE DETAILS OF HOW THAT WOULD WORK.

AND GREG BROWN DID. It doesn’t work. It’s important to know what real science looks like; it’s important to understand the detailed thought processes necessary for case-by-case assessments, thought processes the IOC and other activists who flog this so-called solution hoped you would never encounter. Brown wrote this demonstration with citations, which follow.

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Greg Brown: There really should be no debate that males possess inherent biologically based athletic advantages when compared to similarly aged, trained, and talented females. In middle school, high school, college, Olympic sports, and even community recreational sports, boys and men typically outperform girls and women by 10% to 30% (1, 2, 3 4). To understand this concept simply look at the boys’ and girls’ results for a local high school track meet, or the men’s and women’s results from a local 5K. Even before the onset of puberty, boys run faster, swim faster, jump farther, and throw farther than similarly aged girls (5, 6, 7, 8). The anatomical and physiological factors that contribute to athletic performance have been extensively researched in countless research projects. When speed, endurance, muscle strength, or power are determinants of sports performance, being male endows a person with advantageous anatomy and physiology that a female simply cannot overcome through desire, dedication, training, or nutrition.

Unfortunately, by declaring that sex doesn’t matter in sports, transgender ideology has convinced many people to disbelieve what they can see with their own eyes. Nowhere is this infiltration of transgender ideology more blatant, and harmful, than in the International Olympic Committee’s (IOC) IOC Framework on Fairness, Inclusion and Non-discrimination on the Basis of Gender Identity and Sex Variations (9), in which it states that there should be “no presumption of advantage” regarding transwomen (i.e. males) competing in the female sports category. “No presumption of advantage” when discussing transwomen in female sports is simply absurd because, by all known biological measures, transwomen are indeed male with the accompanying inherent male biological advantages when compared to similarly aged, trained, and talented females. Just because a transwoman is a mediocre male athlete, he should not be granted entry into female sports. An international group of 26 scholars (including yours truly) wrote a rebuttal to the IOC Framework (10), and in polite academic terms, called bullshit on the IOC.

Can Individual Performance Be Used to Discern the Presence of Male Advantage?

This idea of “no presumption of advantage” suggests that each transwoman must be somehow individually evaluated to determine if they do or do not have male athletic advantages. In essence, a case-by-case approach assumes that those transwomen with male advantages would be excluded from the female sports category (which should be all transwomen because they are all male), while those transwomen who are somehow found not to have male advantages (which should be none, since all transwomen are male) would be included in the female sports category.

But how can one define what is indicative of male advantages and what is not? In a reasonable world, being a member of the male sex would automatically exclude someone from girl’s and women’s sports. But we are not living in a reasonable world, and some scholars and policymakers seem to think that there should be a way to justify including males in girls’ and women’s sports.

Let’s work out the details of the oft proposed case-by-case basis of inclusion for transwomen. In sports where individual performances can be easily quantified, such as swimming, running, throwing, or weightlifting, any athlete whose performance is less than a selected female record could be considered to be lacking male advantage. But defining the female performance range as below a set threshold based on female records would open girls’ and women’s sport to the vast majority of non-elite male athletes. And because an athlete can intentionally underperform, especially if they would derive benefits from doing so, one cannot use competition performance as a determining factor for eligibility in the female category.

Consider the following scenarios: The current women’s world track record at 3200m is 8:55.45 (11). Imagine if a transwoman knew that to be eligible to compete in the women’s 3200m race he would only need to run slower than 8:55.45. Remember, the goal for males who wish to be allowed to run in the female category is to underperform, to come in below a certain standard, at least for evaluation purposes, which is quite easy to do and utterly antithetical to the spirit of sport.

Now consider that the fastest 3200m time for a high school boy in the United States in 2024 was 8:48.08 (notice, 1.40% faster than the women’s world record). Also consider that in 2024 there were three high school boys in the United States who ran faster than 8:55.45. Any of those three boys would then be eligible to compete in the female category, and probably win, if they simply did not put forth their best possible effort. In fact, there were thousands of other high school boys who would be eligible for the women’s 3200m race if the threshold for entry was to be slower than the women’s world record.

The fastest 3200m time for a high school girl in the United States in 2024 was 10:02.42 (11). Imagine that if a transwoman (or transgirl) knew that to be eligible to compete in the high school girls’ 3200m race, he would only need to run slower than 10:02.42. Using that time as a threshold, 1,344 high school boys in the United States would therefore be eligible to compete in the girls’ race, and probably win, while not giving their all-out best effort. And many other thousands of high school boys would be eligible if they gave their best effort. If even just a small percentage of those eligible boys are allowed to run in girls’ races, many girls would be excluded from their own category.

These two scenarios clearly illustrate why one cannot use some kind of competition performance metric as the threshold for eligibility to compete in the female category.

Can Lab Testing Be Used to Discern the Presence of Male Advantage?

Hamilton et al. (12) have put forth the concept of using laboratory-based testing of transwomen to ascertain that they do not have retained male advantages. This approach is as flawed as the idea of using some competition performance threshold to determine eligibility for the female category. One reason is that almost all laboratory tests used to evaluate athletic performance are dependent on the athlete giving a maximal effort (13, 14). So once again, a transwoman could simply hold back and be eligible to compete in the female category, providing an incentive to not give his all-out best effort. Putting that very real possibility aside, let’s delve into just one example of why case-by-case physiologically based laboratory testing of transwomen is not a workable way to ascertain the presence or absence of male athletic advantage.

In the case of endurance running, the physiological determinants of performance are quite well known. As explained by Joyner and Coyle (15), the three main physiological factors that determine endurance running performance are maximal oxygen consumption (VO 2 max), the lactate threshold, and running efficiency. In the interest of brevity, I just want to explore some of the reasons why VO 2 max cannot be used on a case-by-case basis to determine eligibility to compete in the female category.

VO 2 max represents the body’s greatest ability to use oxygen to provide energy to fuel the muscles and other tissues (14). VO 2 max has been extensively researched and used in research for over a century, and there are well established normal ranges for VO 2 max in males and females. But while we can measure a person’s VO 2 max and compare it to normative values for their sex and then classify their level of aerobic fitness, we cannot measure a person’s VO 2 max and then use it to determine their sex. In other words, males generally have higher VO 2 max than females, but having a high VO 2 max does not imply that the athlete is necessarily male. Some women have high VO 2 max, in what would normally be considered the male range.

Having a higher VO 2 max predisposes a person to better endurance performance. Males typically have 10% to 50% higher values for VO 2 max than do similarly aged, trained, and talented females, depending on how VO 2 max it is expressed (1, 2, 3, 4, 14, 15). When VO 2 max is expressed as liters of oxygen per minute (L/min; absolute oxygen consumption), it may be up to 50% higher in men than women due primarily to the larger overall body mass of men along with other factors such as higher hemoglobin levels and larger cardiac output. When VO 2 max is expressed as milliliters of oxygen per kilogram of body mass per minute (ml/kg/min; relative oxygen consumption), which accounts for differences in body mass, VO 2 max may still be 10% to 25% higher in men than in women, largely due to men’s greater muscle mass, higher hemoglobin levels, and greater cardiac output. VO 2 max can also be expressed relative to lean body mass, which then eliminates sex-based differences in muscle mass and erases most of the differences in VO 2 max between males and females. However, expressing VO 2 max relative to lean body mass is largely used only for academic purposes and has very little real-world application for assessing fitness.

This brings us to the first problem with using VO 2 max to determine eligibility to compete in the female category—would it be based on absolute or relative VO 2 max? Absolute VO 2 max gives a better representation of total aerobic power transmitted into propulsion of a bicycle, boat, or canoe. But absolute VO 2 max will be higher in a person with a larger body simply because they have more cells that need oxygen. Thus, using absolute VO 2 max might exclude some females from their own category simply because they have a larger body. Relative VO 2 max gives a good measurement for comparing one person to another and to normative data, but relative VO 2 max will most likely be lower in those with more body fat and may not give a true representation of aerobic power in sports like cycling or rowing (17).

There also remains the problem of how to determine what is within the female range for VO 2 max. For example, a 25-year-old woman with a VO 2 max of 54.4 ml/kg/min would rate in the 99th percentile for females (14) but would rate lower, in the 90th percentile, for males. However, elite female endurance athletes have been documented to have VO 2 max values over 60 ml/kg/min. Does that mean these female athletes should be disqualified from the female category because their VO 2 max is above the 99th percentile for women? Does that mean an average 25-year-old male with a VO 2 max of 43.9 ml/kg/min should be included in the female category because his VO 2 max is within the women’s range?

Another problem with using VO 2 max to determine eligibility to compete in the female category comes down to how the test is administered (14). Values for VO 2 max are typically higher when measured on a treadmill than when measured on a bike, so a bike test could result in a transwoman having a VO 2 max in the female range even when he doesn’t. Furthermore, the principle of specificity indicates that a truer measurement of VO 2 max will be obtained if the test is performed using the same mode of exercise as the athlete’s sport. The principle of specificity therefore indicates that runners should be tested for VO 2 max on a treadmill, cyclists should be tested on a bicycle ergometer, rowers should be tested on a rowing machine, and so forth. But what about swimmers, or canoeists? While most exercise physiology labs will have a bicycle ergometer and a treadmill, and many will even have a rowing machine, it’s pretty rare to find a lab capable of measuring VO 2 max while swimming and I’ve never heard of a canoe specific VO 2 max test. And would transwomen triathletes need to have their VO 2 max measured on a treadmill, a bike, and swimming, with all three measurements then falling within the designated female range? Anyone who has performed a VO 2 max test will tell you it is not something you want to do several times in one day.

Hamilton et al. (12) propose measuring VO 2 max before and again after a period of time of undergoing testosterone suppression and estrogen administration in transwomen, and then using some kind of threshold for the amount of reduction in VO 2 max to determine eligibility for the female category. This is problematic because of the effort dependent nature of VO 2 max testing and the incentive for the transwomen to achieve a lower measured VO 2 max after undergoing testosterone suppression. Furthermore, who determines how much VO 2 max must decline for a transwoman to be eligible to compete in the female category? If we go with a 10% reduction in VO 2 max as the threshold for determining that male advantages have been erased, this may not be sufficient. Sleep deprivation can reduce VO 2 max by up to 6% (17), being slightly dehydrated can reduce VO 2 max by 5% (18), and detraining for just a few weeks can reduce VO 2 max by up to 6% (19). Any of these scenarios could allow the transwoman athlete to give a true maximal effort while still demonstrating a reduction in VO 2 max that is not caused by testosterone suppression. Any of these conditions could also be rapidly remedied, and the athlete’s VO 2 max would then increase to a value that was not in the female range.

Furthermore, while measuring VO 2 max is a very standard technique in exercise physiology, it is not perfect. There are many different protocols for increasing treadmill speed and grade to measure VO 2 max, but which one is the right one to determine if a transwoman is eligible to compete in the female category? The same question can be applied to any VO 2 max test, whether it is on a bicycle ergometer, or rowing machine, or other mode of exercise. There also may be up to 2% test-retest variation in the measurement of VO 2 max if testing occurs under ideal circumstances using the same test in the same laboratory (20). Can you imagine the controversy if a transwoman’s eligibility to compete in the female category was denied based on VO 2 max being 0.5% too high in a test with up to 2% variability? You cannot use part of the VO 2 max test as an “A” sample and then retest another “B” sample for verification of the initialresults, like a urine sample test for doping.

Lastly, much like testing athletes for doping, a laboratory would need to be certified to perform the VO 2 max test for eligibility to compete in the female category. This would probably result in a small number of certified laboratories. So, while a urine sample can be frozen, packaged, and shipped to a certified lab for a relatively small cost, you can’t do that with a person for a VO 2 max test. Who would then bear the costs for an athlete to travel to the testing laboratory? And how would the athlete be screened to ensure they were not dehydrated, sleep deprived, or detrained before their certified VO 2 max testing?

When taken at face value, measuring VO 2 max may seem like a simple and practical way to document that a transwoman has experienced a sufficient reduction in performance to make it fair for him to compete in female sports. But as you dig even a little deeper into measuring VO 2 max, it becomes blatantly obvious that there are innumerable barriers to using VO 2 max as a valid and reliable criterion test for determining the eligibility of transwomen (i.e. males) for female sports.

Conclusion

This essay has focused on the challenges of using laboratory-based measurements of only one physiological determinant of athletic performance (i.e. VO 2 max) for determining the eligibility of transwomen (i.e. males) to compete in female sports on a case-by-case basis. The three main physiological factors that determine endurance running performance are VO 2 max, the lactate threshold, and running efficiency. So, the issues of determining what qualifies to be in the female range, units of measure, test specificity, test protocol, test accuracy, and a certified testing laboratory would apply to all three of these factors. And that’s just for endurance running.

Imagine trying to do this for every individual sport, and every position within every team sport, each with its own combination of factors to be tested. It is important to note that for most sports there is considerable debate about which physiological factors are the most important determinants of success, and which tests best measure those factors. It’s not like we take athletes to a lab, perform tests on them, and then hand out the medals. There are still intangibles that cannot be measured which separate the champions from the rest of the competition. And no matter what kind of drivel is put forth in mainstream media, social media, or scholarly publications, transwomen are male, males have inherent biologically based athletic advantages when compared to similarly aged, trained, and talented females, and those advantages remain unchanged in transwomen, regardless of testosterone suppression, estrogen administration, and surgery.

References

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