As far as fitness goes, things change some but it's not hard at all to stay fit. For me, running got a little slower, but not really harder as long as I compare equal effort levels. Strength wise I have gotten a lot stronger although to be fair I was pretty out of shape when I started HRT.
You cannot be too fit although if you keep your bodyfat level really low then you'll stay slender and changes might be less than they would at a higher bodyfat level.
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