How hard should VO2 max training be?

Hi — I just tried one of the vo2 max workouts and was in comfortable zone 4 (heart rate). How hard is it supposed to be? I thought it was supposed to be hard cardio and it wasn’t. It was a good but not brutal leg workout. Is my FTP too low or is it not supposed to be too hard in terms of cardio?

You should hit zone 5. When was your last ftp test?

Ok. Good to know. It’s been 2+ months since my last FTP test.

Sounds like it’s been a productive couple of months!