Starting a new thread as this topic has come up in a number of different threads, mostly discussing polarised training, vo2 sessions, or Seiler intervals.

One metric for measuring work is not the amount of time at a particular power, but the amount of time accumulated over a certain heart rate - i.e. the best approximation of time at actual vo2 max.

So I took a few recent rides, and added up the number of seconds spent above 90% of my max heart rate. I picked ones that were a struggle to finish, but have a variety of interval lengths.

*[Disclaimer - heart rate massively subject to variability; I canâ€™t guarantee the temperature was the same on all these rides, or that I was equally rested]*

5x5mins @ 112% w/3min rests (was supposed to be 6x5 but 5 was enough!)

1020 seconds above 90% HRmax

40/20s (3 blocks of 12 @120%. I think it might have been hot on this day.)

1205 seconds above 90% HRmax

Shortoff +4 (9x3min @ 120% with 3min rests, in 3 blocks of 3. NB this is a 90 minute session)

1256 seconds above 90% HRmax

Would be interested to see what other people can come up with. I havenâ€™t done the Seiler 4x8min intervals yet but Iâ€™ll make that comparison when I come to it.