So which approach is most fair? “Fair is a very subjective word,” says Joanna Harper, a transgender woman, distance runner, and researcher who served on the IOC committee that developed that organization’s current rules. It boils down to whom you’re trying to be fair to, Harper says. “To billions of typical women who cannot compete with men at high levels of sport?” Or “a very repressed minority in transgender people who only want to enjoy the same things that everybody else does, including participation in sports?”. Transgender women’s performances generally decline as their testosterone does. But not every male advantage dissipates when testosterone drops. Some advantages, such as their bigger bone structure, greater lung capacity, and larger heart size remain, says Alison Heather, a physiologist at the Back and body hurts shirt of Otago in New Zealand. Testosterone also promotes muscle memory—an ability to regain muscle mass after a period of detraining—by increasing the number of nuclei in muscles and these added nuclei don’t go away. So transgender women have a heightened ability to build strength even after the transition, Heather says. These folks said it better than I can. Sometimes being fair to one group harms another. Vladimir Afonin Did you specifically study HRT in transwomen? If not, you might want to check it out. Mostly cause this is where most of the research on HRT have focused, not on useful things like improving the health and wellness of trans people. Long story short, it decreases their bone density to that of cis women. Also, fun fact, there is a variety of bone density across sex groups. If you studied physiology I hope you appreciate the variety in human physiology.