From the beginning of this year I’ve started building my cycling form using Zwift. I tried «Build me up». But soon realise that long intervals at 3-4 power levels completely drain me out. My HR was steady during first interval but rose to red zone in the end of last 3 interval. I had to reduce difficulty just to finish the workouts!
So I went for 12 weeks «FTP Builder». I found it much easier.
Now I have 5-6 hour of trainings each week. But I’m facing the same problem: can’t keep same HR in aerobic workouts. Yesterday I tried simple (as I thought) TT Tune-Up - Aerobic 12s in Zwift. Everything was fine for 40 minutes: HR zone 2, same power. But in the last 20 min HR goes to zone 4. What’s wrong with me? Poor muscle endurance? Symptoms of health issues (lack of iron)? Poor hydration or overheating? Or maybe nothing special: I should just keep training?