LONDON, March 5 (Thomson Reuters Foundation) — British female Olympians lined up to criticize the inclusion of male-born transgender athletes in women’s sport on Tuesday, as debate rages over whether male-to-female athletes retain unfair physical advantages after taking cross-sex hormones.

The row over who should compete in women’s sport exploded in October when Rachel McKinnon became the first male-born transgender athlete to win a track cycling world title and was reignited when Martina Navratilova criticized the inclusion of trans women last month.

“I believe it is unfair in the extreme to expect women simply to move over and make way for male-to-female (MtF) transitioning athletes,” Sharron Davies, who won a silver medal at the 1980 Olympics, wrote on Twitter on Tuesday.

“I don’t think you can deny that young boys that have gone through puberty have certain advantages that women will not ever get,” Paula Radcliffe, who holds the women’s world record in the marathon, told the BBC on Tuesday.

Since 2016 the International Olympic Committee (IOC) has allowed male-to-female athletes to compete if their testosterone levels remain below a certain level for a year.

The hormone increases muscle mass, strength and the capacity of the blood to carry oxygen.

When male-to-female athletes take cross-sex hormones their body fat increases and muscle mass decreases, while production of testosterone falls.

But some campaigners and athletes have argued that they retain advantages in strength, height, bone structure and red blood cells — the main source of disagreement.

McKinnon, the cyclist, said such claims were “not based in fact.” “Not one trans person has ever qualified for an Olympics, let alone won a medal,” she told the Thomson Reuters Foundation.

In 2004 the IOC allowed trans athletes in the Olympics if they had had gender reassignment surgery, and female-to-male trans athletes can now take part without restrictions.

But there is little scientific research into trans people in sport.

A 2015 study of eight male to female trans runners by medical physicist and trans woman Joanna Harper found their race times slowed so much that they retained no advantage over non-trans women.

Navratilova, who campaigns for gay rights and suffered abuse when she came out in the 1980s, said on Sunday she was sorry for using the word “cheating” to describe trans sportswomen in a British newspaper two weeks ago.

“All I am trying to do is to make sure girls and women who were born female are competing on as level a playing field as possible within their sport,” Navratilova wrote on her website.

Reporting by Rachel Savage @rachelmsavage; Editing by Claire Cozens. A work of the Thomson Reuters Foundation, the charitable arm of Thomson Reuters, that covers humanitarian news, women’s and LGBT+ rights, human trafficking, property rights, and climate change. Visit http://news.trust.org.

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