A podcast that I just listened to discusses the benefit of increasing threshold interval lengths. As I understand it, the goal is to increase training stimulus by increasing the interval lengths, as opposed to increasing the intensity above FTP. Increasing duration is used for progressive overload.
The question I still have is if I’m at the point where I can do 3x20 SS, should I ever bother with 6x10 SS? I see how changing interval lengths gets you a nice progression, but if the first part of the progression is ‘too easy’, is doing those leaving some adaptations on the table?