When 22-year-old Lia Thomas splashed into the pool at the NCAA Championships in 2022, the ripples extended far beyond the water. The transgender swimmer’s win sparked a wave of debate that’s yet to settle.
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Now, with former President Donald Trump wading into the row—issuing threats to strip funding from states that allow trans athletes to compete—the issue of who gets to play is no longer just about sports. It’s about science, politics, and how society defines fairness.
“This is about protecting women’s sport,” Trump said at a recent rally, repeating a claim that trans women have an unfair edge over cisgender female athletes.
But do they?
The truth, according to scientists, is more complicated.
A Question of Numbers – and Visibility
Transgender athletes make up a tiny fraction of competitors. Fewer than a dozen have ever qualified for the Olympics since the International Olympic Committee changed its rules in 2003. Only one openly trans woman, New Zealand weightlifter Laurel Hubbard, has competed—and she didn’t complete a single lift.
In the United States, the NCAA says “less than 10” trans athletes currently compete in its league of over 500,000. That’s fewer than 0.002%.
Still, the presence of high-profile athletes like Thomas has prompted over half of U.S. states to pass laws banning trans women and girls from competing in line with their gender identity. Critics say those bans are based more on politics than on evidence.
What the Science Actually Says
Dr. Joanna Harper, a British scientist and former competitive runner, has studied this issue for years. She’s also a trans woman herself.
“After two years of hormone therapy, trans women’s performance tends to align closely with cis women in many sports,” she told The New York Times. “But not all advantages go away.”
Puberty plays a role. For those who went through male puberty, testosterone typically leads to bigger bones, greater lung capacity, and more muscle mass.
“Testosterone is powerful,” said Dr. Bradley Anawalt, an endocrinologist at the University of Washington. “Before puberty, boys and girls can compete evenly. After puberty, differences in strength and speed become clear.”
Even with hormone therapy, some of those physical changes—like height or bone structure—don’t fully reverse.
But does that amount to an unfair advantage?
“We don’t know enough yet,” said Dr. Ada Cheung of the University of Melbourne, who advises several sports bodies. “We need more studies, and we need them across different sports.”
One 2021 study of U.S. Air Force personnel found that trans women lost muscle strength after starting hormone treatment. By year two, run times were on par with cisgender women, though some upper-body strength remained slightly higher.
“It’s clear that performance drops,” Harper said. “But how much it drops—and how that affects competition—isn’t always clear-cut.”
More Than Muscle
Supporters of trans athletes argue that sport has never been completely “fair.” Some people are naturally taller, stronger, or faster. Others train with better coaches or have access to better nutrition.
“No one’s suggesting banning tall women from basketball,” said Cheung. “So why single out trans women?”
She believes the debate is less about science and more about values.
“Sports are about inclusion, health, and identity too,” she said.
Still, many women athletes worry about losing out on medals, scholarships, and spots on elite teams.
“It’s about fairness and protecting a level playing field,” swimmer Riley Gaines, a vocal critic of trans inclusion, said last year. “Women fought for these rights.”
Searching for Common Ground
Caught in the crossfire are sports organisations trying to write policy with incomplete data. The NCAA and World Athletics have tightened eligibility for trans women, while the International Olympic Committee now asks individual sports to decide for themselves.
“This is one of those cultural debates where science alone can’t solve it,” Dr. Safer, a hormone expert at Mount Sinai in New York, said. “The question is: what kind of world do we want sport to reflect?”
Even researchers admit the science won’t satisfy everyone.
“There’s no perfect solution,” Anawalt said. “It comes down to deciding what kind of fairness we value—and who we’re willing to include.”
As the debate rages on, one thing is clear: this is no longer just a question of physical strength. It’s a test of society’s willingness to make space—for difference, for data, and for dialogue.
