Transgender women might have more muscle mass than cisgender women 1 to 3 years after hormone therapy, but — this is worth stressing — their physical fitness is comparable.
This is according to a study — “Body composition and physical fitness in transgender versus cisgender individuals: a systematic review with meta-analysis Free” by Sofia Mendes Sieczkowska, Bruna Caruso Mazzolani, Danilo Reis Coimbra, et al — that was published in the British Journal of Sports Medicine.
As such, for the researchers, “while the current body of evidence is of variable quality, and doesn’t look at the potential for any advantage at the elite athlete level, it doesn’t back up prevailing theories about the inherent athletic advantage of transgender women.”
The research deals with an ongoing — i.e. allowing transgender women to compete in sports with those who were assigned female at birth, and, if at all, under what conditions. This is particularly since policies advocating blanket bans on transgender women’s participation in female sports often cite residual advantages from previous testosterone exposure, they add.
Indeed, “previously published studies suggest that hormone therapy may alter body composition in transgender people,” the researchers noted, but added that “the evidence on their functional performance and physical advantage is mixed.”
Here, the researchers scoured research databases for studies comparing the body composition or physical fitness of transgender people before and after hormone therapy with that of cisgender people. In all, 52 studies involving 6,485 people (2,943 transgender women, 2,309 transgender men, 568 cisgender women and 665 cisgender men; age range 14 to 41) were eligible for review.
Pooled data analysis of the findings from 46 of the studies showed that:
- Transgender women’s body composition differs from that of both cisgender men and cisgender women.
- Transgender women have significantly greater amounts of body fat than cisgender men but levels comparable to those of cisgender women.
- While transgender women had more lean mass, a proxy for muscle, there were no observable differences in upper or lower body strength, or in a key measure of cardiorespiratory fitness—maximal oxygen consumption (VO₂ max) — between them and cisgender women.
- Transgender women’s upper and lower body strength and their VO₂ max were also all much lower than they were in cisgender men.
- While hormone therapy was associated with higher amounts of body fat and lower amounts of muscle and less upper body strength 1–3 years after the start of treatment in transgender women, transgender men had less fat, more muscle, and greater strength after hormone therapy.
There may be limitations, noted the researchers, but the findings still allowed them to conclude: “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.”
They added: “Although the current data do not justify blanket bans, critical gaps in literature were found, notably the under-representation of transgender athletes who may retain more ‘muscle memory’.
“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.”
And they emphasized: “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.”
