I don’t know if it has changed or not, but in the sport of figure skating, where males have a definite advantage over females because of their male bodies’ center of gravity which allows them to be able to jump higher and complete more revolutions in the air, the rules required that a male transitioning into a female had to wait until they completed quite a lengthy time on female hormones (several years?? can’t remember exactly how long) before registering to compete as a female.
In other words, a male figure skater can’t just declare himself a female and enter a competition because they would almost certainly decimate the female entrants.
I’m very glad of this. The sport has a very small number of participants at the high levels in the U.S. and the numbers are decreasing as the sport has less visibility on the television (and most people are not watching it, but are streaming made-for-TV movies and series on non-network channels), and to allow males to simply declare themselves female and compete would be a public relations disaster for the sport.
Also, figure skaters are required to complete a series of figure skating tests which increase in difficulty through the highest test, the Senior Test. Two types of tests are required to be allowed to compete in freeskating (which is what you see on TV)–Moves in the Field Senior Test, and Freeskate Senior Test. (Before they Senior test, the test levels that must be completed are Pre-Preliminary, Preliminary, Juvenile, Intermediate, Novice, Junior, and finally Senior–these tests take a typical figure skater years to prepare for, and many skaters have to attempt the tests several times before passing.
The tests are also expensive–the lower-level tests are around $25 or so, but the higher level tests cost several hundred dollars because the judges who are qualified to judge that level must be flown in to the rink where the skater is testing.).
Both males and females take the same tests, so there is no requirement for the transitioning skater to re-take tests that they have already passed. But I’m guessing that trying to pass the higher-level tests while transitioning is a challenge as the body is constantly changing and elements that were learned as one sex would have to be re-learned. So transitioning while trying to complete the tests would discourage a lot of skaters.
At the adult level, I know that there are several trans skaters who have completed their transition. But it’s hard for them. Adults have a harder time with the sport in general because it’s very hard to maintain the high fitness level that a younger skater has, and adult maladies like osteoarthritis, hearing issues, sight issues, weight gain, and aches and pains of aging tend to make it hard to maintain a high technical level. Plus, there’s that annoying job that gets in the way of practice time!