Fatal Flaws In the IOC Sponsored Research Study on Transgender Athletes

On every relevant metric, the comparison groups were vastly disparate, akin to comparing apples to oranges.

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About the Authors

Dr. Greg Brown is a professor of Exercise Science at the University of Nebraska at Kearney and Director of the LOPERs General Studies program. He teaches courses in Exercise Physiology and has also taught Anatomy & Physiology, Sports Nutrition, Research Methods, and Professional Development in Exercise Science Sports Nutrition, and more. His research focuses on the effects of nutritional supplements, physiological responses to exercise, and sex differences in sports performance. He has over 50 peer-reviewed publications and serves as a peer reviewer for numerous academic journals. Brown is an active member of several professional organizations, including the ACSM and NSCA. He enjoys running, fishing, and playing pickleball with his wife, Amber, with whom he has two sons and a grandson.

Dr. Mary I. O’Connor, MD, professor emerita of Orthopedic Surgery at Mayo Clinic and former professor at Yale School of Medicine, is a dedicated advocate for diversity and health equity in orthopaedic surgery. She chairs Movement is Life, a national non-profit aimed at addressing health disparities. Dr. O’Connor has been recognized with Diversity Awards from the American Academy of Orthopaedic Surgery and the American Association of Hip and Knee Surgeons. She also writes a quarterly column titled “Equity360: Sex, Gender, Race, and Ethnicity” in Clinical Orthopaedics and Related Research. A staunch supporter of Title IX and women’s rights, Dr. O’Connor famously participated in the 1976 Yale Women's Crew protest, a pivotal moment for Title IX advocacy. She is also a former national collegiate rowing champion and a 1980 U.S. Olympic team member.

See extended author bios below.

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General Overview

On April 10, 2024, the British Journal of Sports Medicine published a research report entitled “Strength, power and aerobic capacity of transgender athletes: a cross-sectional study” that purports to compare the muscle strength, muscle power, and aerobic capacity of transgender athletes to non-transgender athletes [1]. Although the authors and numerous media outlets are portraying this study as evidence that transwomen (males who identify as women) can fairly compete against women, this is simply not the case.

For starters, the transwomen in this study were as tall or slightly taller than the average man and weighed the same or slightly less than the average man. In this study the transwomen were 7.9 inches taller, 51.4 pounds heavier, and had 26.7 pounds more fat-free body mass than the women in the comparison group. Height, weight, and fat-free body mass all provide their own distinct advantages in numerous sports. And no matter how much they train, diet, and even use anabolic steroids, such as testosterone, women cannot increase their body height or fat-free body mass to that of comparably trained men, even men who suppress their testosterone.

Although the authors claim that both the women and transwomen were “athletes,” the authors provide insufficient information on the frequency, duration, intensity, or sports activity habits of the subjects to validate this claim. This alone should be a fatal flaw for this type of research resulting in the paper being rejected by the reviewers and editor.

Compared to tables of physical fitness, the women in this study were stronger than 90% of women, had lower body fat percentage than 80% of women, and had aerobic fitness comparable to elite endurance athletes. So, the women studied were appropriately classified as athletes. On the other hand, the purportedly athletic transwomen had higher percent body fat than 60-70% of men and more body fat than previously researched non-athletic transwomen. The transwomen had lower hand grip strength than 80% of men but had hand grip strength comparable to previously studied non-athletic transwomen. The transwomen did have aerobic fitness that was higher than 60% of men and was higher than in previously studied non-athletic transwomen. Therefore, the transwomen were, at best, engaged in health promoting aerobic exercise but were certainly not training enough to be considered an equally athletic group for comparison to the women.

With that being said, the transwomen in the study still had 18% higher handgrip strength, 15% more jumping power, and 14% higher aerobic capacity than the athletic women. In other words, the transwomen, despite being less athletic, still outperformed the women. The authors attempt to obfuscate these facts by calculating ratios of strength and power relative to body size and fat-free body mass, but this type of statistical deception has no real-world application in sports. If a 5’3” 134-pound basketball guard with a higher strength to mass ratio tries to drive the lane against a 5’11” 185-pound forward, the guard is probably not going to displace the forward enough to get an easy layup.

The women had a vertical jump that was 1.7 inches higher than the transwomen. But here again, a 1.7-inch advantage in vertical jump is irrelevant when the women were on average 7.9 inches shorter than the transwomen. A 5’11” person with a 14.3-inch vertical jump will still be able to grab the rebound in basketball or block the shot in volleyball against a 5’3” person who has a 16-inch vertical jump.

Lastly, the transwomen had 31% higher measurements of lung volume and 20-23% higher measurements of lung function than did the women. These are typical sex-based differences indicating that the transwomen had retained male advantages in lung size and function.

In conclusion, “Strength, power and aerobic capacity of transgender athletes: a cross-sectional study” demonstrates that taller, heavier, and more muscular non-athletic transwomen are stronger and more powerful than athletic women. Don’t be fooled by the statistical deception of the authors when they try to minimize these differences by calculating ratios of strength or power relative to body size or fat-free body mass. A taller, heavier, stronger, and more powerful male athlete has a clear sports performance advantage compared to a similarly aged, trained, and talented female athlete even when the male suppresses his testosterone.

Detailed Analysis

Before delving into more details in this particular study, we think it’s important to remind the reader of a few important facts. The first is that there is no known biological explanation for a person to be transgender [2]. You cannot get a blood test, DNA screening, genetic test, hormone measurement, MRI, DXA scan, CT scan, or any laboratory test to determine if a person is transgender. And even if there were a test, a transgender identity does not negate the empirical fact that transwomen are male and transmen are female.

Another important fact is that the average man is 5 inches (13 cm or 0.13 m) taller and weighs 30 pounds (13.6 kg) more than the average woman [3]. These height and weight differences persist into sports where even greater sex-based disparity between athletes are common [4-7]. In many sports, being tall has inarguable advantages (e.g., basketball, volleyball, high jump, and others). In other sports, particularly contact and collision sports (e.g., soccer, basketball, rugby, American Football, hockey, baseball, lacrosse, and combat sports), having more body mass has advantages because it makes it easier to displace a lighter weight opponent or to resist being displaced.

One of the many reasons for sex-segregated sports is because of the well-known inherent male advantages in body height and body weight when compared to similarly aged, trained, and talented females. To date, no research, including this paper by Hamilton et al., indicates that being transgender, with or without gender affirming hormone therapy (GAHT), results in shorter body height. And we know that GAHT causes little to no reduction in overall body mass [8, 9].

With these basic facts out of the way, we can now begin our detailed analysis of “Strength, power and aerobic capacity of transgender athletes: a cross-sectional study” by Hamilton et al.

The first important point to note is that this was a cross sectional study, meaning it provides a snapshot of the research participants at the time the data were collected. There is zero information about the health, exercise, or sports habits of the subjects for the months and years prior to the time of data collection. We have no idea about the strength, power, aerobic capacity, and exercise habits of the transgender participants before they started gender affirming hormone therapy (GAHT). This makes it very difficult to draw any cause-and-effect conclusions regarding the effects of GAHT on strength, power, or aerobic capacity in these research participants. For all we know the transwomen could have been weak, obese, sedentary men before starting GAHT.

For the sake of discussion, let's accept the findings of this paper at face value and assume that the research participants accurately represent athletic women and athletic transwomen. Below are the body heights and weights of the women and transwomen from the paper. In sports where height plays a significant role, who is more likely to have the advantage: a 5’11” transwoman or a 5’3” woman? In contact or collision sports, who is better equipped to displace their opponent or resist being displaced: a 185-pound transwoman or a 134-pound woman? Thus, even before considering other factors, it's evident that transwomen retain male advantages in body mass and height.

In this research, Hamilton et al. purportedly compared athletic women to athletic transwomen. We say “purportedly” because the authors did not provide sufficient information on the frequency, intensity, duration, exercise, or sports participation of the research subjects to determine if they were athletes or not. All that was required of the participants to be included in this research project was that they must “participate in a sport at a competitive level or undergo physical training three times per week.” This criterion includes pretty much anything from brisk walking three days per week to engaging in recreational league soccer, competitive powerlifting, or marathon running. So, when evaluating the data for strength, power, and aerobic capacity, it appears that this research compared a group of very physically fit women to a group of unfit males who used GAHT.

Below are the results of the body composition, strength, power, and aerobic capacity testing of the women and transwomen from the study.

The Women Were Very Physically Fit

Based on the data for body composition, muscle strength, and aerobic fitness, the 21 women who were research subjects for this project were very fit. These women were of average body height but weighed 10 kg (22 lbs.) less than average women, had a lower body fat percent than 80% of women, and their hand grip strength was higher than 90% of women [10, 11]. As further evidence of the high physical fitness of these women, their maximal oxygen consumption (VO₂max; the gold standard measurement of cardiorespiratory fitness) was 18% higher than the 95th percentile for women, meaning these women’s VO₂max scores were on par with elite female endurance athletes. Comparing the body composition, handgrip strength, and aerobic fitness of these women to reference standards indicates these women were highly fit and most likely can accurately be described as athletes.

The Transwomen Were NOT Physically Fit

The body composition, muscle strength, and aerobic fitness of the 23 transwomen in this project were not in line with what would be expected of athletes. While the authors contend this lack of physical fitness is due to GAHT, we contend it is more likely that the transwomen were not engaged in exercise commensurate with optimizing athletic performance. We reiterate that the authors provide no data on the frequency, intensity, and duration of exercise or sports training of the research participants necessary to demonstrate the truth of their assertion that the transwomen were athletes. Until they do, the more scientifically parsimonious explanation is that the transwomen were simply not very athletic.

The transwomen studied by Hamilton et al. were of average or slightly above average body height for men and were only slightly (1.2 kg; 2.6 lbs.) below average in body mass [12]. The transwomen had a higher body fat percent than 60% of comparably aged men [10] and higher body fat than previously researched non-athletic transwomen [13-15]. The purportedly athletic transwomen studied by Hamilton et al. were well below average (scoring in the 20th percentile) in hand grip strength compared to men [10], but were on par with hand grip strength of non-athletic transwomen [13, 16]. And the VO₂max measurements of the transwomen in Hamilton et al. were slightly above average (scoring in the 60th percentile) when compared to men [10] and were above what has been previously observed in non-athletic transwomen [15].

Taking all of this together, it is reasonable to conclude that Hamilton et al. studied a group of transwomen who may have engaged in health promoting aerobic exercise. However, they were certainly not engaged in vigorous strength training or other exercise programs necessary for competitive athletic success.

Comparing Dissimilar Groups

When evaluating the data on body composition, hand grip strength, and VO₂max of the women and transwomen examined by Hamilton et al., and comparing these findings to reference normative data, it becomes evident that this was a comparison of apples to oranges. The women appeared very athletic based on their low body fat, high hand grip strength, and high VO₂max. Conversely, the transwomen did not appear athletic, evidenced by their high body fat, low handgrip strength, and only slightly above average VO₂max. Because of this, it is not surprising that Hamilton et al. resorted to deceptive statistics to portray the transwomen as equal to or less athletic than the women.

Right from the start we can see that the transwomen were 7.9 inches (0.2 meters) taller, weighed 51.4 pounds (23.3 kg) more, and possessed 26.7 pounds (12.3 kg) more fat-free body mass than the women (fat-free body mass primarily consists of muscle). Besides height and weight, another major factor that separates males from females in sports performance is the larger amount of muscle mass enjoyed by men. Quite simply, more muscle mass equals a greater potential for strength, power, and aerobic capacity. These inherent male advantages retained by the transwomen in body height and muscle mass are simply not attainable for women through efforts such as hard work, diet, or even the use of anabolic steroids like testosterone.

The hand grip strength of the transwomen was 18% higher than the women. Hand grip strength is often used as a proxy for upper body strength, and men typically have more upper body strength than women. While the difference in hand grip strength between the transwomen and women is lower than is typically expected between men and women, the non-athletic transwomen were still stronger than the very fit women. Who is going to be able to grip and swing a golf club or baseball bat better: a woman with a grip strength of 76 pounds or a transwoman with a grip strength of 90 pounds? Who will be better able to hold onto a rugby ball, palm a basketball, or grip an oar in rowing?

To further illustrate this point, anabolic steroids generally increase muscle strength by 5-20% and are almost universally banned in sports because of their performance enhancing effects, which create an unfair competitive field [17]. Yet, by the simple virtue of being biologically male, these non-athletic transwomen have an 18% strength advantage over very athletic women.

The transwomen’s vertical jump height was lower than the women’s by 1.7 inches (4.3 cm). Considering that the transwomen had 51.4 pounds (23.3 kg) more weight to lift off the ground, it’s not surprising that the unfit transwomen had a shorter vertical jump than the athletic women. However, in a sporting context, factoring in the longer arms that come with taller body height, the transwomen would have an almost 10-inch higher reach than the women. Who would win the battle for a rebound or get over the net to block a spike in volleyball: a 5’3” woman who can jump 16” or a 5’11” transwoman who can jump 14”? The transwoman would have the advantage.

To illustrate the difference in strength between women and transwomen even further, even though they did not jump as high as the women, the transwomen produced 831 watts more power during jumping than the women. While 831 watts is difficult to relate to, imagine trying to resist being displaced by someone who can produce 15% more power with their legs than you can while battling for a soccer ball, or trying for a tackle in rugby, or when jockeying for position under the basket. And once again, all indicators suggest that these are not athletic transwomen who have this relatively large power advantage over athletic women.

The authors then present the hand grip strength, vertical jump, and power relative to body mass, fat-free body mass, and hand size to argue that this somehow removes the obvious male advantages. But this is a deceptive statistical practice that has no relevance to sports. In sports, absolute strength is a more important factor than strength relative to body mass. While athletes may be grouped into weight classes in some sports, none classify athletes based on a ratio of muscle strength to fat-free body mass or power relative to body mass. Were this the case, a 265-pound heavyweight wrestler could contend against a 104-pound lightweight wrestler possessing the same strength-to-mass ratio.

The data for aerobic capacity present a bit of a conundrum. Although the transwomen showed a numerically higher VO₂max, this difference was not statistically significant. Typically, males have a VO₂max that is 40-50% higher than females when measured in milliliters per minute [18]. However, in the current data, the transwomen’s VO₂max is only 14% higher than that of the women. This conundrum is most likely due to the exceptionally high aerobic fitness of the women (recall that their VO₂max is on par with elite endurance athletes) and their low body fat, in contrast to the transwomen who exhibited lower aerobic fitness and a higher amount of body fat. Although not statistically different, the 14% higher VO₂max represents a 14% greater power output when pedaling a bike or rowing a boat. When races are often decided by fractions of a second, a 14% male advantage in aerobic power output will be very hard for a woman to overcome.

Lastly, Hamilton et al. measured the lung capacities of their participants (shown in the table below). Forced Vital Capacity measures the amount of air that can be forcefully exhaled, providing an indication of lung size. Forced Expiratory Volume in 1 second measures how much air can be exhaled out in 1 second, reflecting breathing capacity, while Peak Expiratory Flow rate measures the speed of exhaled air, also indicating breathing capacity. All of these measurements indicate male typical advantages in lung size and function.

Overall, the paper by Hamilton et al. is a fatally flawed, offering us little to no insight into the effects of gender-affirming hormone therapy on the athletic ability of transwomen. The inclusion criteria regarding exercise and sports participation were so broad, and the sample size so small, that it’s impossible to draw any meaningful conclusions. Additionally, on every relevant metric, the comparison groups were vastly disparate, akin to comparing 23 apples to 21 oranges.

For example, the comparison group of women were highly athletic and physically fit, well above that of the average woman. Based on the body composition and muscle strength data, the transwomen were not particularly athletic, ranking well below average for men yet still exceeding women in hand grip strength and muscle mass. This demonstrates a retained male advantage in sports performance. In terms of aerobic fitness, the transwomen were somewhat fitter than the average man yet were as fit as women in the 95^th percentile of normative reference data. Moreover, respiratory data indicated that the transwomen retained male-pattern advantages in lung size and function.

Overall, despite attempts by the authors, the IOC, and trans rights activists to spin these data by comparing the results to the statistically misleading metric of fat-free body mass, the data actually show that comparing males to females is not a fair comparison for ensuring a level playing field in sports, regardless of testosterone suppression. Instead, it’s like substituting Navel oranges for Granny Smith apples when trying to bake an apple pie.

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Extended Author Bios

Dr. Greg Brown is a professor of Exercise Science at the University of Nebraska at Kearney where he also serves as the Director of the LOPERs General Studies program. His primary teaching responsibilities are undergraduate and graduate courses in Exercise Physiology, but he has also taught courses in Introductory Anatomy & Physiology, Sports Nutrition, Research Methods, and Professional Development in Exercise Science. His research has evaluated the effects of nutritional supplements on the physiological response to exercise, the physiological responses to various types of exercise, effective teaching in the exercise science program, and sex-based differences in sports performance. He has authored or co-authored over 50 peer reviewed publications and serves as a peer-reviewer for over two dozen academic journals. Two of his most recent publications include research demonstrating that boys run faster than girls before puberty and a criticism of the IOC framework on fairness, inclusion and non-discrimination on the basis of gender identity and sex variations. He is a member of the American College of Sports Medicine (ACSM), the National Strength and Conditioning Association (NSCA), the Association of American Educators (AAE), and the Academic Freedom Alliance. He is one of the founding members of Academics for Academic Freedom at UNK.

He and his wife (Amber) have two adult sons, one daughter-in-law, and one absolutely adorable grandson. His hobbies include running, hunting, fishing, studying history, playing pickleball with his wife, and watching movies.

Mary I. O’Connor, MD is professor emerita of Orthopedic Surgery at Mayo Clinic and past professor of orthopaedics and rehabilitation at Yale School of Medicine. She is chair of Movement is Life, a national non-profit focused on addressing health disparities. Dr. O’Connor has championed diversity in the orthopaedic surgery profession for her entire career. In 2023 she was the recipient of both the American Academy of Orthopaedic Surgery and the American Association of Hip and Knee Surgeons’ Diversity Awards. Dr. O’Connor writes a quarterly column entitled “Equity360: Sex, Gender, Race, and Ethnicity” in Clinical Orthopaedics and Related Research. In her May 2023 column on “Sex and Fairness in Sports,” she advocated for female-only women’s sports to preserve a level playing field for female athletes and has published rebuttals to several letters to the editor from those who support the inclusion of transwomen in women’s sports.

A staunch advocate for Title IX and sex-based women’s rights, Dr. O’Connor was part of the legendary 1976 protest by Yale Women’s Crew over the lack of a locker room for the women at the boathouse. In what is heralded as the first stand for Title IX in college athletes, Dr. O’Connor and 18 of her teammates stripped in front of the Yale athletic director with Title IX written on their bare chests and backs to read a statement that began with, “These are the bodies that Yale is exploiting.”  This story was picked up by The New York Times and International Herald Tribune. By the following spring an addition was completed to the boathouse with a locker room for the women. Dr. O’Connor went on to a successful athletic career as a national collegiate champion, stroke of the bronze medal U.S. National Team Women’s Eight at the 1979 World Rowing Championships (competing against eastern-bloc women who were doping on testosterone), and member of the 1980 U.S. Olympic team. On occasion, she rows with old teammates and they go faster than ever before.

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References

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