Blocking Puberty Doesn’t Block Biology

A flawed assumption about puberty is reshaping sports policy and putting children at risk.

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About the Author

Dr. Colin Wright is an evolutionary biology PhD, Manhattan Institute Fellow, and CEO/Editor-in-Chief of Reality’s Last Stand. His writing has appeared in The Wall Street Journal, The Times, the New York Post, Newsweek, City Journal, Quillette, Queer Majority, and other major news outlets and peer-reviewed journals.

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Debates over transgender inclusion in female sports have focused heavily on the question of fairness. Mounting scientific evidence—including several comprehensive reviews—has established beyond a doubt that males who undergo typical male puberty retain a lasting athletic advantage over females, even if they later suppress testosterone. This advantage is due to irreversible structural and physiological changes triggered by puberty, such as increased bone size, muscle mass, and aerobic capacity. In response, activists and some sports governing bodies have shifted their argument. They now claim that fairness can be preserved if trans-identifying males begin medical transition early enough to avoid male puberty entirely.

This idea has gained ground in policy. In 2022, World Athletics updated its eligibility criteria for the female category to permit “male-to-female transgender athletes” to compete, provided they “have not experienced any part of male puberty beyond Tanner Stage 2 or before age 12, whichever is later,” and have “since continuously maintained their testosterone levels in serum (or plasma) below 2.5 nmol/L.” The policy reflects the widely held belief that male athletic advantage arises only with puberty, and that if puberty is blocked early enough then males can compete on equal footing with females.

A new study published in the journal Exercise, Sport, and Movement directly challenges this foundational claim. Titled “Sex Differences in 1600-m Running Performance and Participation for Children Aged 6–12 yr,” the study offers some of the clearest evidence to date that boys outperform girls in running events well before the onset of puberty.

Researchers Mandy W. Christensen and Christine M. Griffiths set out to answer two important questions: Do sex-based differences in aerobic running performance exist in prepubescent children? And if so, are these differences best explained by innate biology or the fact that girls tend to participate in sports at lower rates than boys? These questions have real policy relevance, especially as sports organizations increasingly rely on assumptions about developmental biology to shape eligibility criteria.