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FINA, world swimming's governing body, has voted 71.5% in favor of new rules on transgender athletes, ruling that only those who transitioned before the age of 12 will be permitted to participate in women's competitions. According a report by the Associated Press, the new rules will apply to all events beginning on Monday.

The new rules come amid controversy over the advantage some say transgender women have over biological women, and the ensuing effect it has on the integrity of women's sports. At the governing body level, calls for changes to policy have centered around the testosterone levels of transgender women and exactly how long it takes for the awaited adaptations in muscle mass, strength and power to occur.

Though the new policy bars transgender women from elite competition -- most notably University of Pennsylvania swimmer Lia Thomas -- the new policy calls for the creation of an "open competition" category that would permit transgender women who do not fall under the new criteria.

"No one quite knows how this is going to work. And we need to include a lot of different people, including transgender athletes, to work out how it would work," James Pearce, spokesman for FINA president Husain Al-Musallam, told the AP. "So there are no details of how that would work. The open category is something that will start being discussed tomorrow."

FINA's vote occurred after hearing presentations from three specialist groups -- an athlete group, a science and medicine group, and a legal and human rights group -- who have been working together to form the policy. Such work began after the International Olympic Committee gave new recommendations on the matter of transgender women last November.

Although the focus of such issues had been on testosterone levels up to that point, the IOC's new advice called for evidence as to where and when a performance advantage exists.

The issue of transgender women in swimming was highlighted when Thomas, an Olympic hopeful, won the NCAA swimming championship in the 500-yard freestyle in March.