Trans sportswomen hit back at Martina Navratilova, after the tennis champion said "its insane and it's cheating" for transgender women to be allowed to compete in women's sport.
"A man can decide to be female, take hormones if required by whatever sporting organisation is concerned, win everything in sight and perhaps earn a small fortune, and then reverse his decision and go back to making babies if he so desires," 18-times Grand Slam winner Navratilova wrote in The Sunday Times.
Navratilova's comments are "disturbing, upsetting, and deeply transphobic," said Rachel McKinnon, who in 2018 became the first transgender woman to win a world track cycling title, reigniting a debate over whether trans women have unfair physical advantages in sport.
Under rules brought in by International Olympic Committee (IOC) in 2016, athletes transitioning from female to male can now participate without restrictions.
Male to female competitors must have kept their levels of testosterone, a hormone that increases muscle mass, strength and haemoglobin, which affects endurance, below a certain level for at least 12 months.
The Wimbledon champion, who has campaigned for gay rights and suffered abuse when she came out in the 1980s, argued trans women have unfair physical advantages.
"A man builds up muscle and bone density, as well as a greater number of oxygen-carrying red blood cells, from childhood," she said.
The Duchess of Cambridge speaks with ex tennis players Kim Clijsters (second from right) and Martina Navratilova (right) on day one of the Wimbledon Championships at The All England Lawn Tennis and Croquet Club, Wimbledon.
Jul 14, 2018; London, United Kingdom; Julia Lemigova, Martina Navratilova, Billie Jean King, Ilana Kloss, Philip Brook, HRH The Duchess of Cambridge and HRH The Duchess of Sussex react in the Royal Box during the Novak Djokovic (SRB) and Rafael Nadal (ESP) match on day 12 at All England Lawn and Croquet Club. Mandatory Credit: Susan Mullane-USA TODAY Sports
Stephen Fry with Martina Navratilova (right) in the Royal Box on day day Ten of the Wimbledon Championships at the All England Lawn Tennis and Croquet Club, Wimbledon.
La extenista Martina Navratilova. EFE/Archivo
BEVERLY HILLS - FEBRUARY 11: Martina Navratilova and Julia Lemigova at the 2017 Clive Davis Pre-Grammy Gala at the Beverly Hilton Hotel on February 11, 2017 in Beverly Hills, California. (Photo by Scott Kirkland/PictureGroup)BEVERLY HILLS - FEBRUARY 11: Martina Navratilova at the 2017 Clive Davis Pre-Grammy Gala at the Beverly Hilton Hotel on February 11, 2017 in Beverly Hills, California. (Photo by Scott Kirkland/PictureGroup) *** Please Use Credit from Credit Field ***
Martina Navratilova and Julia Lemigova on day twelve of the Wimbledon Championships at the All England Lawn Tennis and Croquet Club, Wimbledon.
Serena Williams and Lucie Safarova with their trophies alongside Martina Navratilova after the women's singles final on day fourteen of the French Open at Roland Garros on June 6th, 2015 in Paris, France
Martina Navratilova (left) arriving for the Sports Personality of the Year Awards 2012, at the ExCel Arena, London.
Prime Minister David Cameron talks to tennis player Martina Navratilova during a reception for the 2012 Laureus Awards in 10 Downing Street, central London.
Britain's Prime Minister David Cameron (front row centre) poses for a photograph with sports personalities (back row left-right) Sean Fitzpatrick, Gary Player, Nadia Comaneci, Novak Djokovic, Boris Becker, Oscar Pistorius, Steve Regrave, Mark Spitz, (front row left-right) Kelly Holmes, Tanni Grey-Thompson, David Cameron, Edwin Moses and Martina Navratilova, during a reception for the 2012 Laureus Awards in 10 Downing Street, central London.
USA's Martina Navratilova during the match with her partner Czech Republic's Jana Novotna against USA's Lindsay Davenport and Switzerland's Martina Hingis in the Ladies' Invitation Doubles final on day thirteen of the 2011 Wimbledon Championships at the All England Lawn Tennis Club, Wimbledon.
Former tennis player Martina Navratilova and Sir Richard Branson watch the match between Belarus' Victoria Azarenka and Czech Republic's Petra Kvitova on day ten of the 2011 Wimbledon Championships at the All England Lawn Tennis and Croquet Club, Wimbledon.
USA's Martina Navratilova during the Ladies' Invitation Doubles final.
Martina Navratilova in the Royal Box on Centre Court
Martina Navratilova greets Queen Elizabeth II as she attends the Wimbledon Lawn Tennis Championships on Day 4 at the All England Lawn Tennis and Croquet Club in London.
Sunderland Chairman Niall Quinn (right) and former Women's Tennis Champion Martina Navratilova in the stands
Sir Richard Branson and Martina Navratilova watch the Ladies final between Venus and Serena Williams during the 2009 Wimbledon Championships at the All England Lawn Tennis and Croquet Club, Wimbledon, London.
Martina Navratilova (left) and Rula Lenska during The All England Lawn Tennis Championship at Wimbledon.
Tennis ace Martina Navratilova ahead of her appearance in the Liverpool International Tennis tournament.
Tennis star Martina Navratilova (left) arrives with actress Rula Lenska for the 50th Sports Personality of the Year awards presentation at the BBC Centre, London.
Martina Navratilova (r) is presented with her trophy by The Duke of Edinburgh (l) afterr winning in the mixed doubles final
NO COMMERCIAL USE: Former Wimbledon champion Martina Navratilova (right) receives her Waterford Crystal plate from HRH The Duchess of Gloucester during the Champions Parade at Wimbledon.
NO COMMERCIAL USE: Former Wimbledon champions Martina Navratilova (left) and Chris Evert share a joke during the Champions Parade at Wimbledon.
Martina Navratilova and Chris Evert
Martina Navratilova sings along with Sir Cliff Richard on Centre Court this afternoon (Wednesday) as rain stopped play in the men's quarter finals. Photo by Adam Butler/PA.
The Princess of Wales and her son Princess William applaud Conchita Martinez and Martina Navratilova after the Womens' Singles Final at Wimbledon, London.
REFEREE ALAN MILLS ESCORTS MARTINA
NAVRATILOVA AND CONCHITA MARTINEZ ONTO
THE CENTRE COURT FOR THE LADIES FINAL.
25-JUN-93 ... Wimbledon Tennis ... Martina Navratilova, Czechoslovakia
MARTINA NAVRATILOVA AND MARK WOODFORDE
HOLD UP THEIR WIMBLEDON MIXED DOUBLES
TROPHY ON CENTRE COURT. IT IS MISS
NAVRATILOVA'S 18TH WIMBLEDON TITLE.
Martina Navratilova of the USA in action
Ladies Singles Champion for a record ninth time Martina Navratilova holds aloft the trohy on the centre court.
Ladies' Singles champion Martina Navratilova (l) shows off the trophy, as runner up Steffi Graf has to be content with a bouquet of flowers
Martina Navratilova celebrates victory
Martina Navratilova admires the trophy as she holds it aloft
Czech-born American Tennis star Martina Navratilova, about to play at Surbiton.
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Navratilova "trades on age-old stereotypes and stigma against trans women, treating us as men just pretending to be real women," McKinnon told the Thomson Reuters Foundation.
Scientific research into trans people in sport is rare. A 2015 study of eight male to female trans runners found their race times slowed down to an extent that they retained no advantage over non-trans women.
Jen Wagner-Assali, who finished third to McKinnon in the 35-44 year-old category world championship race, argued the Canadian's victory was not fair. McKinnon said her rival had previously beaten her in 10 of 12 events.
"This idea that men will transition or pretend to transition to enter women's sport is offensive," Natalie Washington, a trans activist who plays amateur women's football in Britain, told the Thomson Reuters Foundation.
"It misrepresents the huge struggle that the vast majority of trans people have to go through."
Navratilova expressed support for Caster Semenya, the two-time 800-metre Olympic women's champion, in her case against the International Association of Athletics Federations (IAAF), which is being heard at the Court of Arbitration for Sport this week.
The IAAF introduced a rule in April 2018 that would have forced women with naturally-high testosterone levels to take hormone therapy to lower them to compete in track events from 400 metres to one mile, had it not been challenged by her and Athletics South Africa.
Semenya, who was forced to take a gender test when she won the world championship at the age of 18 in 2009, has hyperandrogenism, a condition characterised by higher than usual testosterone levels.
"Leaving out sprints and longer distances seems to me to be a clear case of discrimination by targeting Semenya," Navratilova said.