I just did a 1 hour zone 2 workout on the trainer. The first 40 minutes I felt like I was pedaling at near threshold, despite being in low zone 2 (60% FTP). My breathing felt like threshold as well, open mouthed and all. Then suddenly, at around the 40 minute mark my RPE dropped like a stone and 70% FTP felt like I was doing a recovery ride. My breathing also changed and I was nose breathing through the rest of the workout. Strangely my HR remained pretty stable through the whole workout.
I didn’t take in any nutrition during the ride (my lack of preparation in fact) and this has been a relatively stressful week, training and everything else included. Any idea why my RPE would be so high for 40 minutes and then just plummet? If I can prepare for that I think I could plan out my workouts better.