The entire losing muscle mass thing seems to vary from tranny to tranny, but those who lose enough to compare to cis women often had little to no muscle to begin with. AKA not people who were athletes prior to transition. Does HRT effect muscle mass? Sure. But it takes a long fucking time. And having male bone structure would always provide an advantage. Do I think trans people should be disallowed from participating in sports? God no, too many of them are fat, some exercise and fresh air would probably do them a lot of good. They should just have their own category. We do the same for lots of disabled people, the special olympics is honestly quite inspiring when you think about it