It started out as an experiment , I had a good hunch my ftp was around 260-270 , so , I thought I’d start conservatively and used 4 min @290 , 8 min @260 and 16 min @240 . These were roughly a bit over , at , and under threshold . I managed these fine so just tweeted up a bit and was at 250/280 and 300 before I “ lost focus” . I think the heart rate is a useful metric because youcan keep track of drifting as you progress through the intervals .Quoting Seiler , “ it’s just about collecting minutes at the high work rate “, which obviously boils down to being consistent. He also encourages you to ride your slower / steady rides easier than you’re probably used to , so I have been enjoying pooling around paths , canals etc on gravel bike. All in all it’s a recipe that I am enjoying .