A typical ride is simply out the driveway and down the road. It's fairly rural and totally flat. I generally ride with my HR at 140-150. I'm not fast, due to other health/heart issues (heart infection years ago). So, going slower is not what I'd like, as it would mean I'm below 13MPH and that's too slow! I'll put it this way, my legs never get tired. But my heart does get fatigued after 2 or so hours.
I was thinking about trying sprints or pushing harder. Not sure.