Doing some VO2 structure for first time in a year, and not totally sure how to approach the target zones in my scenario. And not in the AT beta, nor is it clear that it’s ready to solve my HR-related question 
After 5 years cycling, last year was a massive increase in structured volume for me - responded way better than any prior training, launched by doing TR SSB HV2 outside. It has been great for long endurance, TTs, and even helped short end of my power curve significantly - but my max HR is down about 10 points.
I understand we typically expect to lose ~1BPM/year with age. But I’m seeing a much bigger drop - specifically, some max efforts over past year:
- 2020 April (pre-SSB HV) - 192 - ramp test
- 2020 Dec - 184 - all out 1 min uphill sprint KOM efforts done multiple days, multiple each day
- 2021 - rarely hit 180 - max 182, despite many power PRs in online races in the 10+ min range
Another point that confounds this for me - on 1 hour fairly steady FTP effort, I plateaued around 173BPM - took about 40 mins to get there, and then stayed around that for 20 mins until a surge at the very end got me up to 177. Which makes me think threshold is still up around 175 - main difference being it takes me WAY longer to get there now than prior years. Just 3 years ago, I used to crack 180 on pretty much any TR O/U workout probably thanks to a too-high ramp test FTP.
With that context, I’ve recently done Mills and Spanish Needle, peaking at 172 and 174 HR respectively using the 120% default power target. They were not “easy” - but also not the post-ramp test completely dead feeling at the end - I did some high Z2 for a half hour or so after each of them. This is about 94-95% of my 2021 peak HR, but barely 90% of the ~190-191 I’d expect to be at based on aging.
Would you:
- Say good enough % of demonstrated recent max HR to be productive intensity and stay as planned?
- HTFU and try pushing power up to make sure I’m spending more time in at least the high 170 BPM range, maybe cracking 180, and not pay attention to the power target as much? I have hesitated doing so because if it implodes the workouts two intervals in, I’m not sure that’s a gain… hard to know what is “enough”
- Go outside and hammer some segments as hard as possible to re-validate max HR?
- Get off the bike and sprint up a hill to validate max HR where I have zero fitness? (could be dangerously stupid…)
Other ideas?