I run 25-30 miles a week. When I started HRT, within a week my times got much slower so I had to readjust my form to be more efficient. It seemed like I lost a lot of strength, but not the proportional muscle mass. After a few weeks on HRT, I started getting some visible muscle mass loss, especially in the arms and legs. My chest, shoulders, and back seem about the same as pre-HRT, though.