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New research has looked at dozens of studies comparing the body composition and fitness of cisgender and transgender people, and it suggests that while there are differences in lean muscle mass on average, there are no significant differences in fitness performances between trans and cis women.
The rest of this article is behind a paywall. Please sign in or subscribe to access the full content.Spurred by politicians and the media, many sports federations have put forward blanket bans on the participation of trans and non-binary people in sports, even at a non-professional level. The bans have often relied on limited evidence, shaky science, or downright sexist assumptions that cis men are naturally better at every competition than women.
One of the most bizarre examples was the International Chess Federation (FIDE) effectively blocking trans competitors from women-only competitions in 2023 – a move that several national chess associations have chosen to ignore as nonsensical.
The scientists looked at 52 studies featuring a total of 6,485 people whose age varied from 14 to 41. Of those, 2943 were transgender women, 2309 were transgender men, 568 were cisgender women, and 665 were cisgender men. The studies were different in focus and approach. For example, only 16 directly assessed physical activity, and only 7 adjusted for influential factors like hormone levels or nutrition. Still, the meta-analysis provides some important insights.
Between one and three years after beginning gender affirming hormone therapy (GAHT), trans men had less fat and more muscle, while trans women had more fat and less muscle. In general, trans women retained more lean mass (a proxy for muscle) compared with the average cis woman, but their fat levels were the same, and the average lean mass for both was well below that of the average cis man.
This is in line with previous work showing that hormone therapy produces strong effects on the body, aligning a person's physiological processes to their gender identity at a cellular level.
In terms of fitness, the study found no observable differences between the upper and lower body strength of cis and trans women. An important measure of cardiorespiratory fitness – known as maximal oxygen consumption (VO₂ max) – also showed no difference.
“The convergence of transgender women’s functional performance with cisgender women, particularly in strength and aerobic capacity, challenges assumptions about inherent athletic advantages derived solely from [gender affirming hormone therapy] or residual lean mass differences,” the researchers wrote in the paper.
According to these findings, it would seem that blanket bans on trans people participating in sports lack solid scientific support. That said, the study does have its limitations. One highlighted by the researchers is the possibility that elite athletes who transition after attaining a high fitness level might retain a higher level of performance.
The problem is that there simply aren't enough trans people reaching those levels in sports to even begin doing that kind of analysis. This leads to a chicken and egg situation: to see if elite trans athlete have an advantage in sport, you actually need trans athletes at those high levels.
“Ideally, to resolve speculation, future long-term, longitudinal studies should prioritise performance-specific metrics in transgender athletes. However, one should be aware of the scarce number of transgender athletes, particularly in the elite sport, which complicates the feasibility of conducting powered studies involving high-performance transgender athletes within specific sport disciplines,” the authors write.
"Although the review has some limitations, such as the lack of studies on elite athletes and the lack of studies on specific sports events, it gives us two clear messages," Adrián Carrasco Munera at the Madrid Society of Family and Community Medicine, who was not involved in the research, told Science Media Centre España. "[T]here is no evidence to support the claims that trans women have greater strength and endurance than cis women, and... exposure to testosterone prior to hormone treatment in trans women does not lead to better physical conditions for sport."
The team calls for more studies to bring additional detail and rigor to this field.
“Considering this context of imperfect evidence and despite the methodological challenges, continued research into physiological as well as psychosocial trajectories among transgender athletes with diverse demographics and clinical characteristics remains essential for developing equitable frameworks that balance justice, inclusion and scientific rigour.”
The research was published in the British Journal of Sports Medicine.
