Transgender athlete Joanna Harper explains what happened after her transition:
In 2005, nine months after starting HRT, I was running 12% slower than I had run with male T levels; women run 10-12% slower than men over a wide range of distances. In 2006 I met another trans woman runner and the she had the same experience. I later discovered that, if aging is factored in, this 10-12% loss of speed is standard among trans women endurance athletes. The realization that one can take a male distance runner, make that runner hormonally female, and wind up with a female distance runner of the same relative capability was life changing for me.