deapee

You sure about that?
So your theory is that two twins - one an endurance athlete, one a sedentary individual - will have no difference in testosterone levels throughout their bodies?

I think endurance training, as part of an active lifestyle, will absolutely ensure that your T is at a level where it's 'supposed to be.'
I think too much or too little endurance training can have a negative impact on hormone levels.
And I also think that unless there is something *else* causing concern, you shouldn't worry about what riding a bike does to your T levels. That being said, if something else is causing concern, you should probably discuss it with your doctor...