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Analysis

Median change after about 12 months of hormone treatment, adult transgender women

After about a year of testosterone suppression and estrogen, how much do testosterone, hemoglobin, muscle size, lean mass and strength change in transgender women?

Coverage: Studies published 1999-2020; Air Force fitness records 2004-2018

Contained in Transgender women on hormones: what changes in a year, and Air Force fitness tests over 2.5 years.

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What this dataset measures

These are the two most-cited bodies of evidence on whether testosterone suppression removes the male athletic advantage: before-and-after clinical studies, gathered in the Harper et al. (2021) systematic review, and the only study of real fitness-test performance over time (Roberts et al. 2021). Using every adult 12-month study group in the review, rather than one study, avoids picking a favorable result.

Geography
United States, Europe
Unit of observation
Study group and measure; fitness measure and time band
Update cadence
As new before-and-after studies are published
Curator
FactHub Research Team

Supporting files

Source snapshots, manifests, quality reports, documentation, and other materials used to produce or review this release.

  • analyses.json Derived table · application/json · 16.7 KB (17,090 bytes)

    Every saved-analysis result in this dataset, as computed by build.js.

  • build.js Transformation manifest · text/javascript · 4.2 KB (4,317 bytes)

    Node.js script that computes every saved analysis from the two curated tables.

Saved analyses

Median change after about 12 months of hormone treatment, adult transgender women

Question: After about a year of testosterone suppression and estrogen, how much do testosterone, hemoglobin, muscle size, lean mass and strength change in transgender women?

Result: Median change after about 12 months: testosterone -95.6% (12 groups), hemoglobin -7%, muscle size -6.4%, lean body mass -4%, strength +0.5% (range -7.1% to +2%).

Operation: For each measure, the median of the percentage changes across included study groups; range = lowest and highest group. Testosterone change computed from each group's before and after values; other changes as printed by Harper et al., or computed from before and after means where not printed.

Scope: Study groups of adult, mostly untrained transgender women in Europe and the U.S., 1999-2020.

Estimates with uncertainty
EstimateValueUncertaintyMethodn
Testosterone -95.6 % change after about 12 months (range -97.8 to -48.8) range Median of the percentage changes in the included study groups; the range is the lowest and highest study group. 12
Hemoglobin (red blood cells) -7 % change after about 12 months (range -14 to -4.6) range Median of the percentage changes in the included study groups; the range is the lowest and highest study group. 5
Muscle size -6.4 % change after about 12 months (range -9.5 to -1.5) range Median of the percentage changes in the included study groups; the range is the lowest and highest study group. 4
Lean body mass -4 % change after about 12 months (range -5.4 to -0.8) range Median of the percentage changes in the included study groups; the range is the lowest and highest study group. 8
Strength 0.5 % change after about 12 months (range -7.1 to 2) range Median of the percentage changes in the included study groups; the range is the lowest and highest study group. 5

View this analysis

  • Participants were adults and mostly untrained; no study measured athletes or adolescents through this design.
  • Small groups (11 to 249 women) and few groups per measure (4 to 12).
  • About 12 months only; Harper et al. found strength, lean mass and muscle area still above women's after 36 months, but with too few studies to chart.

Sources

  1. Harper J, O'Donnell E, Sorouri Khorashad B, McDermott H, Witcomb GL (British Journal of Sports Medicine) Systematic review, Tables 2-5: per-study changes in lean body mass, muscle cross-sectional area, strength and hemoglobin or hematocrit, with each study's testosterone before and after treatment, in transgender women on hormones. Free copy

    Retrieved November 5, 2026. CC BY 4.0. Open access under CC BY 4.0; FactHub republishes the extracted numbers with attribution.

    Reliability: Peer-reviewed study. Peer-reviewed systematic review of 24 studies of non-athletic transgender women, from Loughborough University and partners; no specific funding and no competing interests declared.

  2. Roberts TA, Smalley J, Ahrendt D (British Journal of Sports Medicine) Table 4: U.S. Air Force fitness-test push-ups, sit-ups and 1.5-mile run times of 46 transgender women before and during hormone treatment, compared with the average Air Force woman and man under 30.

    Retrieved November 5, 2026. Copyright BMJ; numbers reported as facts. FactHub republishes the table's means, differences and confidence intervals as facts, with attribution; the article text is not redistributed.

    Reliability: Peer-reviewed study. Peer-reviewed study of U.S. Air Force medical and fitness records, 2004-2018, by military and academic pediatricians; no specific grant. Fitness tests measure endurance, not maximal strength, and the comparison is to an Air Force average, not matched controls.

  3. Scharff M, Wiepjes CM, Klaver M, Schreiner T, T'Sjoen G, den Heijer M (Endocrine Connections) Cross-check of the largest 12-month study group: 249 transgender women in the European ENIGI cohort, grip strength 41.8 kg before and 40.0 kg after 1 year; median testosterone 17.9-18.5 nmol/L before and 0.4-0.8 nmol/L during treatment by clinic (Table 1). Free copy

    Retrieved November 5, 2026. CC BY 4.0. Open access; numbers republished with attribution.

    Reliability: Peer-reviewed study. Multicenter prospective clinical cohort in Amsterdam, Ghent and Oslo; authors declare no conflict of interest.

  4. Wiik A, Lundberg TR, et al. (Journal of Clinical Endocrinology & Metabolism) Cross-check of the Wiik study group: thigh muscle volume fell 5% and quadriceps cross-sectional area 4% in 11 transgender women after 12 months, while strength was maintained.

    Retrieved November 5, 2026. Copyright Endocrine Society; numbers reported as facts. Numbers republished as facts with attribution.

    Reliability: Peer-reviewed study. Prospective study of 11 untrained transgender women at Karolinska Institutet, Stockholm; funded by Stockholm County Council and two foundations; no conflicts declared.

License: FactHub's selection, cleaning and combined tables are licensed under CC BY 4.0. Source data keeps the terms listed above (terms).

Limitations and reproducibility

Reproducible from public sources: Both curated tables are transcribed from published tables (Harper et al. 2021, Tables 2-5; Roberts et al. 2021, Table 4). build.js computes every saved analysis from them. The largest 12-month group (Scharff 2019) and the Wiik 2020 group were cross-checked against the original papers.

  • Nearly all participants were adults, and none were competitive athletes. No before-and-after study has measured athletic performance in transgender girls.
  • The 12-month medians count each study group once, regardless of size, and pool different muscles and strength tests.
  • The Air Force comparison is to an average woman, not to matched women with the same training.
  • Changes after 12 months are not charted; the review found too few studies to say whether losses continue.

Publications using this dataset

Version details

The exact citing versions, and the version of this dataset each cites.

  • Article trans-girls-athletic-advantage — version 3 (published) cites version 1
  • Article trans-girls-athletic-advantage — version 2 (published) cites version 1
  • Chart hormones-year-testosterone-vs-strength — version 1 (published) cites version 1
  • Chart air-force-run-gap-on-hormones — version 1 (published) cites version 1

Node: dataset:testosterone-suppression-athletic-measures:1:analysis:twelve-month-change