Drawing on 52 studies, this review challenges assumptions about athletic advantage between cis- and transgender athletes, while highlighting major evidence gaps in elite and sport-specific performance.
Study: Body composition and physical fitness in transgender versus cisgender individuals: a systematic review with meta-analysis. Image credit: Shutterstock.AI Generator/Shutterstock.com
Researchers have recently conducted a systematic review and meta-analysis to compare body composition and physical fitness between transgender and cisgender individuals, and published their findings in the British Journal of Sports Medicine.
Long-running debate over transgender inclusion
Transgender women are individuals assigned male at birth who identify and live as women, while cisgender women are those assigned female at birth whose gender identity aligns with that assignment. Women’s sports exist separately to ensure fair competition for cisgender women. For years, the question of transgender women competing in female sports has sparked intense debate. This has led to proposals that transgender athletes should only compete if they don’t create significant competitive imbalances.
Research has challenged some concerns that transgender women would dominate women’s sports, largely because testosterone suppression therapy reduces certain physiological characteristics associated with male puberty. In fact, transgender women remain underrepresented in elite athletics, although the authors note that underrepresentation alone cannot be used to draw conclusions about competitive advantage.
The IOC established a framework prioritizing fairness, inclusion, and non-discrimination, rejecting blanket bans and advocating for sport-specific eligibility criteria. Critics argue this relies on insufficient research and impractical assessments, potentially compromising protections for cisgender female athletes.
Some researchers contend the IOC’s ‘no presumption of advantage’ principle overlooks studies suggesting transgender women may retain muscle mass, strength, and other physical characteristics after testosterone suppression. However, systematic reviews comparing transgender women who underwent gender-affirming hormone therapy and cisgender women have reported mixed and inconsistent findings, highlighting ongoing scientific uncertainty.
Largest synthesis to date of transgender fitness research
The current systematic review with meta-analysis examines existing research on body composition and physical fitness in transgender women compared to cisgender women, with secondary comparisons across other gender groups. It also examined how hormone therapy duration affects outcomes, compared responses between transgender men and women, and explored the impact of puberty suppression.
All relevant articles were obtained from PubMed, Web of Science, Embase, and SportDiscus. Inclusion criteria comprised studies of transgender individuals comparing body composition or physical fitness pre-to-post gender-affirming hormone therapy or versus cisgender controls.
The initial database search identified 1705 studies. After removing duplicates, 1067 publications were screened. A total of 52 studies that fulfilled the eligibility criteria were included in the review, and 43 in the meta-analysis. This analysis included 6485 individuals, 2943 transgender women, 2309 transgender men, 568 cisgender women, and 665 cisgender men.
All participants were between 14 and 41 years of age. Of 52 studies, only 16 assessed physical activity levels, and most did not control for activity status. The selected studies used different methods to assess physical activity, including METs (metabolic equivalents), questionnaires, measures of exercise frequency and duration, and simple activity classifications.
Study designs included 22 prospective cohorts, 9 retrospective cohorts, 17 cross-sectional studies, 3 randomized controlled trials (RCTs), and a quasi-experimental study. Only 7 studies adjusted for confounders, most commonly body composition, age, hormone levels, and nutrient intake.
A significant variation in hormone therapy types and dosages was noted. Transgender women primarily received estradiol, in the form of oral tablets, patches, or gel, often combined with antiandrogens such as cyproterone acetate or spironolactone. Transgender men primarily received testosterone undecanoate or enanthate via injection, with some using gels. Dosing varied by administration route, age, and clinical context.
Therapy duration ranged from 3 months to 14 years, with most studies following participants for 1–3 years. Twelve studies included participants who had undergone gender-affirming surgery, and six reported the use of puberty suppression.
Physical fitness outcomes in transgender women
Compared to cisgender women, transgender women showed no statistically significant differences in relative fat mass, relative lean mass, upper-body strength, lower-body strength, or aerobic capacity. However, the authors emphasized that the quality of evidence ranged from very low to low certainty, with substantial heterogeneity and wide confidence intervals in several analyses, limiting the precision of these estimates.
Despite having slightly higher relative lean mass than cisgender women (standardised mean difference (SMD) 0.19), transgender women showed no significant differences in upper-body strength (SMD 0.54) or lower-body strength (SMD 0.05). Aerobic capacity, measured as maximal oxygen consumption (VO₂ max), was also not significantly different between groups. The authors stress that a lack of statistical significance does not imply identical performance, rather, it indicates that consistent differences were not detected in the available data.
After 1–3 years of hormone therapy, transgender women experienced increased fat mass and decreased lean mass and upper-body strength. The authors noted that, despite persistent differences in lean mass, these changes were not consistently associated with differences in functional performance, suggesting that lean mass alone may not directly translate into strength advantages.
The authors cautioned that lean mass and performance outcomes were often derived from different studies, preventing direct correlations between muscle mass and athletic performance. They also emphasized that the available data largely reflect non-athlete or recreationally active populations, rather than elite competitors.
Physical fitness outcomes in transgender men
Transgender men showed body composition and strength metrics that were intermediate between cisgender women and cisgender men for some outcomes, even after an average of four years of hormone therapy. However, the authors reported that transgender men continued to differ significantly from cisgender men in several measures, including relative lean mass and upper-body strength.
Findings challenge simple claims of inherent advantage
This systematic review and meta-analysis found that while transgender women tend to have higher lean mass than cisgender women, they show no consistent or statistically significant differences in commonly measured physical fitness outcomes, such as strength and aerobic capacity, after 1–3 years of hormone therapy. The authors emphasize that these findings do not demonstrate equivalence in athletic performance and do not directly address sport-specific competition outcomes.
The authors highlighted substantial limitations in the available evidence. Most studies were small, lacked statistical adjustment for key confounders, and rarely assessed physical activity or training status. Elite athletes and sport-specific performance measures were largely absent from the literature.
The authors conclude that future research should include larger, well-controlled, longitudinal studies that follow transgender athletes over time, account for training history and competition level, and assess sport-specific performance outcomes. Such evidence is needed to inform nuanced, sport-specific eligibility policies rather than broad generalizations about advantage or disadvantage.
