HILLS/FLATS/TRACK/TRAILS APPLIED TO GENERAL TRAINING

I am writing an article about the general use of hills, running on flat terrain such as the Canal, track workouts and Trail Running and how runners training for competition, factor this different type of terrain/elevation, etc when running their mileage throughout the week. I know there are many theories and lots of opinions on this but I am sure some of the runners on the team choose their running routes due to the fact that they do not have hills, are hilly, are soft surface, are trails only, etc.

I am simply trying to collect some sample answers/comments from people who take these factors strongly into consideration.

If you have an opinion that can be supported with some sound reasoning and you think others might benefit or it has helped you with your training please feel free to comment.

thank you

Max