Martina Navratilova has long advocated against the inclusion of transgender athletes in the female category for obvious reasons, one of which is a competitive advantage.
The issue of transgenders in sports is becoming a widespread problem due to many being of the opinion that they should compete in a separate category. The biggest issue is when people who were assigned male at birth compete now as females considering anatomical differences in the bodies of men and women which gives the former men a competitive advantage.
It was proven in practice when a few athletes that competed as males before started competing as females and immediately broke records which stood for years. It's clear that Navratilova is arguing for something that is more than just a personal opinion but rather a fact. Speaking to the Times, Navratilova once again explained her stance:
"I think the best idea would be to have “biological female” and “biological girls” categories and then an “open” category. It would be a category for all-comers: men who identify as men; women who identify as women; women who identify as men; men who identify as women; non-binary — it would be a catch-all."
One of many biological advances men have is lung capacity with men having a larger one which is one of the examples she cited. She also cited a generally bigger frame, bigger muscles, stronger muscles etc. There have been others who also support a similar stance to Navratilova.