I recently completed my first double century (STP), and it wiped me out, even though I have done back-to-back-to-back-to-back... centuries during tours without too much trouble. My new goal is to be able to do back-to-back double centuries a year from now, but I don't know what the best training approach is. Should I just keep doing back-to-back long rides on the weekends, and slowly dial up the mileage, or would it be better to concentrate on extremely long one-day rides with a recovery day afterward?
Also, how much does interval training help for long-distance rides? I teach high school, so the amount of time I have to train will dramatically decrease come August, and if anyone here has any suggestions for using short rides to train for very long rides, I would appreciate it.