Men in Women's Sports: The Biological Advantages That Testosterone Suppression Cannot Erase

Women's sports categories do not exist because women are weaker than men in some vague general sense. They exist because male puberty produces specific, measurable, and largely permanent physiological changes that affect athletic performance — and because absent a protected female category, women and girls would be largely excluded from elite competition. The question of whether trans-identified men should compete in female categories is, at its core, a question about whether those physiological advantages persist after hormone therapy. The evidence says they do.

Testosterone during male puberty drives changes that affect athletic performance:

• Heart size and output: Male hearts are on average 25–30% larger than female hearts relative to body size, enabling greater cardiac output and oxygen delivery
• Lung volume: Males have 10–15% greater lung capacity than females of the same height
• Bone density and structure: Males develop denser, heavier bones — particularly in the hips (narrower, more mechanically efficient for running), shoulder width, and limb length. These changes are structural and largely permanent.
• Muscle mass and fiber type: Testosterone drives development of fast-twitch muscle fibers and greater absolute muscle mass. Males have on average 40–60% more upper body strength than females and 20–30% more lower body strength.
• Hemoglobin and red blood cells: Males have higher hemoglobin concentrations (approximately 15% higher), enabling greater oxygen transport to muscles
• Height: Males are on average 5–6 inches taller than females, conferring biomechanical advantages in many sports

These changes occur during puberty and are not dependent on circulating testosterone continuing at male levels — the structural changes have already been made. Lowering testosterone in adulthood does not rebuild female skeletal architecture, reduce lung volume, or reconstruct muscle fiber distribution.

Hilton & Longman (2020), British Journal of Sports Medicine: Systematic review of 24 studies on hormone therapy in trans-identified men. Findings: after 2 years of feminizing hormone therapy, trans-identified men retained advantages over females in muscle mass, strength, and other performance-relevant parameters. The review concluded that 'the advantage to transwomen [their terminology] is not removed by hormonal therapy.'

Wiik et al. (2022), British Journal of Sports Medicine: Measured muscle strength, size, and body composition in trans-identified men after 12 months of feminizing hormone therapy. Found significant reduction in muscle mass but persistent advantage over biological females. Trans-identified men retained thigh muscle volume approximately 13% greater than female controls.

Roberts et al. (2021), British Journal of Sports Medicine: Study of US Air Force personnel. Found trans-identified men who had undergone hormone therapy retained advantages in push-ups and sit-ups after 2 years — advantages that were 'likely clinically meaningful.'

The pattern across studies: hormone therapy reduces but does not eliminate male athletic advantages. The reduction takes years and is incomplete. At the elite level, where competitions are decided by margins of 1–3%, even a 5% retained advantage is decisive.

Lia Thomas (swimming): Lia Thomas competed as Will Thomas on the University of Pennsylvania men's swimming team, ranked 462nd nationally in the 500-yard freestyle. After two years of hormone therapy, Thomas competed in the women's NCAA division, winning the 500-yard freestyle national championship — defeating Olympians and breaking university records. Riley Gaines tied Thomas in the 200-yard freestyle; Thomas was awarded the trophy, Gaines received a plastic replica.

Brooke Slusser (volleyball, SJSU): San Jose State University volleyball player Brooke Slusser publicly described the distress of being required to share hotel rooms and locker rooms with a male-born teammate during competition travel. The SJSU women's team went 32–1 and won the Mountain West Conference championship; multiple opponents forfeited rather than compete against a male-bodied player.

Multiple swimming and cycling records: A trans-identified cyclist in Canada, Veronica Ivy, held multiple world records in age-group cycling while competing as female. Multiple female swimmers have had records broken by trans-identified male competitors who had not previously held records at comparable levels in male competition.

HeCheated.org maintains a comprehensive, continuously updated database of competitions, scholarships, records, and opportunities that female athletes have lost to male-born competitors. It is the primary documentation resource for this issue.

Women's sports categories were created specifically to give female athletes equal opportunity to compete at their biological performance level — because without protected female categories, the sex-based performance gap means females would be systematically excluded from the top tiers of competition in almost every sport.

If the purpose of the female category is to ensure female athletes have competitive opportunities, then including male-born athletes in the female category defeats that purpose, regardless of those athletes' gender identity. This is not a complicated argument. It does not depend on hostility toward trans-identified individuals. It depends only on the reason female categories exist.

The question 'Why shouldn't trans women be allowed to compete as women?' obscures this. The clearer framing: 'Why should men be allowed to compete in women's sports?' — where 'men' refers to the biological category that underwent male puberty — makes the issue immediately visible. The answer that male puberty creates irreversible athletic advantages that make female competition unfair is the same answer whether the man in question is trans-identified or not.