Women's tennis legend Martina Navratilova. (Getty Images)

Martina Navratilova, who won multiple Wimbledon and U.S. Open titles and is considered among the best female tennis players in history, denounced the idea that transgender females -- men who claim they are women -- can compete fairly in women's sports, stating "it's insane and it's cheating."

"[I]t is surely unfair on women who have to compete against people who, biologically, are still men," she wrote in The Sunday Times on Feb. 17. "[F]airness should always be valued and strived for" and "unfairness introduced through human action and chemical means should be condemned and outlawed."

Transgender "female" Rachel McKinnon, who won the women's Masters Track cycling world championship in October 2018. (YouTube)

Navratilova, who came out as a lesbian in 1981, wrote her commentary on transgender athletes partly in response to being criticized by transgender "female" cyclist Rachel McKinnon, a biological male who won the women's Masters Track cycling world championship in October 2018.

Navratilova had also been attacked for tweeting, “You can’t just proclaim yourself a female and be able to compete against women. There must be some standards, and having a penis and competing as a woman would not fit that standard.”

The tennis legend explains that, after the criticism, she researched the topic of transgenderism at length and found that the evidence only confirmed her views.

"[I]f anything, my views have strengthened," she wrote in The Times. "To put the argument at its most basic: 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."

"It’s insane and it’s cheating," said Navratilova. "I am happy to address a transgender woman in whatever form she prefers, but I would not be happy to compete against her. It would not be fair."

Tennis champion Martina Navratilova. (YouTube)

"Simply reducing hormone levels — the prescription most sports have adopted — does not solve the problem," she wrote. "A man builds up muscle and bone density, as well as a greater number of oxygen-carrying red blood cells, from childhood. Training increases the discrepancy. Indeed, if a male were to change gender in such a way as to eliminate any accumulated advantage, he would have to begin hormone treatment before puberty. For me, that is unthinkable."

Navratilova continued, "Hundreds of athletes who have changed gender by declaration and limited hormone treatment have already achieved honours as women that were beyond their capabilities as men, especially in sports in which power rather than skill is paramount. McKinnon is just one example."

"That may uphold the International Olympic Committee’s charter, which holds that 'the practice of sport is a human right,' but it is surely unfair on women who have to compete against people who, biologically, are still men, she said.

Transgender "female" Rachel McKinnon, center, a biological male who won a women's cycling championship.

"I still believe that fairness should always be valued and strived for, and that unfairness introduced through human action and chemical means should be condemned and outlawed," said Navratilova, who won nine Wimbledon titles (Grand Slam Singles), four U.S. Open titles, and two French Open titles.

Navratilova, 62 and a U.S. citizen, also denounced the "tyranny" of the politically correct gender police. "I also deplore what seems to be a growing tendency among transgender activists to denounce anyone who argues against them and to label them all as 'transphobes,'" she wrote. "That’s just another form of tyranny. I’m relatively tough and was able to stand up for myself in my Twitter exchange with McKinnon, but I worry that others may be cowed into silence or submission."

She continued, "Here’s how I concluded my Twitter spat: 'Rachel [McKinnon], you may be an expert on all things trans, but you are one nasty human being. Attack, attack, attack. I will not take it from you. You did not engage; you bullied."