This is awesome, thank you for the detailed explanation!! Now I better understand what I've been doing in spin classes the last 5 years π
We do a "PTP" at the start of class, which is 2 minutes as hard and heavy as we can. This sets our "zone 5" for the ride (we call it red zone). My max heart rate varies 176-181 during that period (age 43).
Then during the ride we do various lengths in different zones (using colors instead of numbers). Usually 30 seonds to 3 minutes in length. I also do some HIIT training classes during the week.
So, perhaps I've been training to increase my VO2 max and didn't even realize it.
Thank you, I really appreciate this.