@WillRunForPizza I use the Heart Rate Reserve formula which exactly matches
@Dopey 2020's Karvonen formula. For me, I use the following zones that come from Daniels:
In real life, my 5k average pace is never 171-173. Rather I may see my HR hit 171-173 at the very end of a 5k race. It's important to note that it's realistic for your maximum HR to drop over time. So what was 173 bpm today, may not be 173 bpm 5-10 years from now. In practical terms, my HR average for M is usually around 145-150, and HM is around 148-154.
For me, I use HR data as a secondary measure. I focus on effort during the run, knowing I have goal paces that are adjusted based on hills and T+D. Post-run, I'll look at HR as a secondary measure to help confirm my internal feelings about the pace. If my HR drifts too much from past experiences, then I adjust my effort level for the next subsequent runs. Otherwise, I use HR data as a means to evaluate gains in fitness in a zoomed out manner (which I recently previously dove into earlier in this thread).
As for max HRs in the 200s, I've seen it from some other runners. So it can certainly be realistic. All you need is for the watch to be precise. If doesn't matter if the watch is accurate as long as under the same conditions it gives you the same value output. For our purposes as recreational runners, that's good enough to be able to use it to track changes within a run or between runs for the use in zones.
