I'm doing the ZA rides and workouts too. Did Workout 2 as a lone workout yesterday morning (because it's been withdrawn from the group workout schedule), and Workout 3 as a group workout last night. Oh my word, that was tough! 1.5 mins at 275W and 1.5mins at 315W, which should have felt easy compared with what the Gorbies I was doing in the summer, but with so little time to recover in between I just found it utterly nails. I came out as a sprinter (haha, 6'3", 11st and can't do a chin-up!) which I think just reflects that my endurance is rubbish.