Men on average have an advantage over women running 5K because they have larger heart and lungs
And that's still true. I probably do have a larger heart and lungs, because hormones don't really change that. But they do change every other part of my cardiovascular system. My red blood cell count is reduced, my VO2Max is reduced and my blood oxygen levels are reduced.
As I understand it, my heart and lungs don't give me an advantage here, because the other parts of my cardiovascular system become the limiting factor.
much higher muscle ratio, lower body fat percentage (even for overweight men) and a different bone structure.
All of this changes with hormones! I used to have 15% body fat. I haven't changed weight during my transition, but my body fat is now at 20%, and is located in traditionally female locations. My thighs rub together when I run now! And the reason my body fat has gone up, but my weight hasn't changed, is because I've lost muscle mass. My strength is greatly reduced, especially in my upper body.
And my body fat levels still aren't at the levels they will ultimately end up at. It's still slowly increasing
Cross sex hormones might have a minimal affect on body fat but very little.
It's more than minimal!
And ultimately, the reason I don't mark my runs as assisted anymore is because I have done the research and looked at my own results and I am confident I am not carrying an unfair advantage over other women. If I believed for a second that I was, I'd change all of my results to assisted in a heartbeat.
I do understand that not everyone agrees with me, whether they doubt my right to run as a woman, or simply believe that I do have an advantage. But all I can do is what I believe to be the right and fair thing. And that's what I'm doing. Even if you do disagree with me, this was a choice I made after a lot of personal consideration. My historical pre-transition runs are all marked as assisted precisely because it was the right thing to do.
But, I am a woman, and I will run as a woman. I won't let other people decide my identity for me, though I do acknowledge their right to disagree with me. And as long as the evidence continues to suggest that I'm running without advantage, I will continue to run openly with and as a woman.