Biological Differences Between Men and Women Matter in Sports

When comparing similarly aged, gifted, and trained males and females, males’ inherent biological advantages tip the playing field unalterably in their favor.

Written by

Alliance Defending Freedom

Published June 27, 2023

Editor's note: The following piece was written by Dr. Gregory Brown, professor of exercise science in the physical activity and wellness laboratory of the Department of Kinesiology and Sport Sciences at the University of Nebraska Kearney. It originally appeared at National Review.

As schools across the country are closing one calendar year and preparing for the next, state legislatures are battling a question that will have repercussions both inside and outside school walls: Should schools keep sports separate by biological sex or allow students to compete based on one’s gender identity?

Currently, 22 states (most recently, Missouri, just this month) have passed laws requiring that only those who are of the female sex can participate in girls’ and women’s sports. And while states such as Connecticut are being challenged in court for allowing biological males to compete against females, states such as West Virginia and Idaho are on the opposite end of the equation, facing lawsuits for standing up for women and girls in sports. In the case of West Virginia, the ACLU is representing a young male student who wants to compete in girls’ sports. Even at a prepubescent age, does this student have inherent biological advantages?

As an exercise physiologist, my focus is on the biological factors that influence health and human performance. The nervous, muscular, cardiovascular, respiratory, endocrine, and other systems all influence how a person adapts to exercise and can ultimately determine how someone will perform in sports. But one of the most important factors that influences adaptations to training and performance in sports is sex, because sex influences every system and every cell in our body.

The sex-based anatomical and physiological differences between males and females give males athletic advantages when compared to similarly aged, gifted, and trained females — no matter the age range. Records from USA Track & Field show in the eight-and-under age group and the nine-to-ten-year-old age group, boys run faster, jump longer, and throw farther than similarly aged girls in every event. Evaluations of fitness testing from around the world in children as young as three years old show that boys perform better than girls of the same age on tests of throwing, muscular strength, muscular endurance, and aerobic fitness. Prepubertal sex-based differences are smaller than the differences after puberty but are still meaningful in competition.

Puberty magnifies the sex-based differences in performance, with teenage boys and adult men outperforming girls and women by 10–15 percent in running, 15–20 percent in jumping, and 30–60 percent in strength. None of this is owing to better training, nutrition, coaching, or motivation. Males have inherent biological advantages, such as taller body height, more lean body mass, more muscle mass, greater muscle strength, larger hearts and lungs, higher maximal oxygen consumption, and stronger bones than similarly aged, gifted, and trained females.

Even after a male has undergone hormone therapy, research shows that, while those biological advantages decrease, they are still far more prominent than similarly aged and trained women. Men have 30–60 percent higher muscle strength than women, and undergoing testosterone suppression decreases that strength by only 0–9 percent — a far cry from an even playing field for even the strongest female athletes.

Yes, some women are taller than some men. Some women are stronger and can run faster than some men. But the tallest women are shorter than the tallest men, the most muscular men have significantly more muscle mass than the most muscular women, the strongest men are much stronger than the strongest women, and the fastest men are much faster than the fastest women. When comparing similarly aged, gifted, and trained males and females, the males’ inherent biological advantages tip the playing field unalterably in their favor.

A person cannot have a blood test, CT scan, MRI, genetic screening, or any other standard or specialized laboratory test to determine a transgender identity. Therefore, if a male identifies as a girl or woman, biological sex is still present, and it is reasonable to conclude that he still has inherent male athletic advantages. Based on information in four different scholarly review papers by four different groups of scholars; separate reviews conducted by World Rugby, FINA, World Athletics, and the Sports Councils of the United Kingdom; and 27 peer-reviewed primary-research papers from many different research groups around the world, the current evidence indicates that identifying as transgender — with or without the use of puberty blockers, testosterone suppression, and/or cross-sex hormones — does not erase the inherent male athletic advantages.

Many of these truths have been articulated in legal briefs and expert declarations filed in the lawsuits occurring around the country to protect women’s sports, including in one heard by the Second Circuit Court of Appeals on June 6, in which I myself submitted a declaration. My hope is that the judges who will decide these cases will fully consider the clear biological evidence in favor of fairness for women and girls in sports.

Alliance Defending Freedom

ADF team members contributed to the writing and publication of this article.

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