Reacción a "A review finds no differences in physical performance between trans women and cis women, even though they have more muscle mass"

The work by Sieczkowska and colleagues, to be published in the British Journal of Sports Medicine (part of the BMJ group), consists of a systematic review followed by a meta-analysis of transgender people who underwent gender-affirming hormone treatment for at least three years, comparing them with cisgender men and women using various measures including fat-free body mass and upper and lower limb strength.

In my opinion, the study has two significant flaws, which are only detectable after a thorough and careful reading. Firstly, the study presents a significant discrepancy between the conclusions drawn in the abstract and the limitations acknowledged in the discussion, which is worth highlighting. In the abstract, the authors state that their results ‘do not support theories of inherent athletic advantages in trans women versus cis women’.

This formulation suggests to the reader a strong and general conclusion, with clear implications for public debate. However, in the discussion, the authors themselves explicitly acknowledge that the lean mass and physical performance data do not necessarily come from the same cohorts or study designs, which prevents direct correlations from being established between muscle mass and strength or functional performance.

This acknowledgement invalidates any robust inference about the existence or absence of athletic advantages. From a methodological point of view, the evidence presented does not allow for conclusions in either direction. What the data show is, at most, an absence of detectable differences in certain performance metrics in the short and medium term, but not a refutation of the hypothesis of inherent athletic advantages.

The problem is not the quality of the analysis—which is cautious in its discussion—but the rhetorical shift between sections: a strong conclusion in the abstract, which is what most readers and journalists read, and an admission of substantial uncertainty in the body of the article. This type of formulation can lead to simplified or overgeneralised interpretations that are not fully supported by the data.

In a scientifically complex and socially sensitive field, the distinction between “finding no evidence” and “demonstrating absence of effect” is not a minor nuance, but a basic principle of scientific reasoning. In this case, the study provides relevant information, but does not settle the question that the abstract itself suggests it has resolved.

Secondly, both the introduction and the discussion lack a developmental perspective that is essential in these cases, specifically the three-phase action of testosterone (during gestation, mini-puberty after birth and from puberty onwards), nor do they mention recent studies on the effects of feminisation treatment (estradiol + cyproterone acetate) on the epigenome.