This discussion has been locked.
You can no longer post new replies to this discussion. If you have a question you can start a new discussion

Performance condition vs VO2max and elevation

My apologies if I'm rambling in this post - I'm trying to make sense of the P.C. vs VO2max and the effect of trail runs vs flat runs on these metrics. I don't really have a specific main question here. Any comments to any of my statements/questions, or corrections of misconceptions, are welcome and hopefully some useful experiences could emerge.

I think I've understood the basics of the P.C. - it's a real-time assessment of my performance compared to my VO2max.

- As it's a real-time assessment, it would be normal that the PC is higher at the beginning of a run than it is at the end when fatigue starts to show. (This development is always true for me at least)

- I usually get my PC score after about 1 km of running. After about a year of running with this metric I've never once scored more than +4 or less than -4. I guess that could be an indication that the VO2max estimated by the FR945 is quite close to my real VO2max - or is it just an indication that the watch algorithms for PC and VO2max are aligned? 

- Until the most recent FW update, my PC and VO2max scores have been based on Running activities only - which are mostly low intensity asphalt runs with the occasional hill. My current VO2max is 52 and my 1km PC score on these flat runs is almost always in the range from 0 to +3. 

- However, I do most of my exercising using the Trail run activity, on trails with mostly uphill running. I've only done one such run after the FW update that enables Trail VO2max (a 7x2min zone 5) and my PC score was -1. It remains to see if the scores continue to be negative, and if so, I expect my VO2max to be adjusted down; in that case the PC should adjust as well giving me less negative scores on trail runs and very positive scores on flat runs?

I also use Runalyze to calculate effective VO2max for my runs. Runalyze always gives lower scores than Firstbeat/Garmin, but the trend is the same: Lower scores (32-38) on hilly trail runs and higher scores (42-46) on flat runs.

This huge difference in the scores from Runalyze vs Garmin makes me wonder which numbers are most correct. (Runalyze 6mo average is around 40 and Garmin estimate is 52) I do realise the VO2max is not an accurate measurement, more like an indication of my fitness in different types of exercises. But I had expected them to be more aligned than this. Anyone with similar experiences?

Looking at Garmin only and the difference in PC scores on flat vs uphill/trail runs, I also wonder how well Garmin's VO2max estimation represents my fitness. Just to give some rough numbers, on flat runs, I can stay within zone 2 for an hour of running at avg 6:00 min/km, while in my typical uphill/trail run I'll be in zone 3 from just a few minutes in, at avg 7:00 min/km. I guess it's hard to say without a laboratory test.

  • One way to doublecheck Firstbeat/Garmin's estimation of Vo2max is to check the comparable race times they provide, do they look realistic?

    I also use Runalyze and it always scores my Vo2max lower than Firstbeat/Garmin, in some cases far lower.  It *seems* to me that Runalyze's estimation is less sophisticated and takes less into account that Garmin's does.  For example, I did a treadmill incline "run" with the Stryd Workout app (coded as "run" per garmin) where the incline was 14% throughout.  I maintained an effort that would be equivalent to a Zone 2 to 3 "run" even though my pace was far slower than it would be on flat terrain.  Firstbeat/Garmin estimated that Vo2max pretty much inline with what I would expect (51) whereas Runalyze apparently didn't take the incline into account and scored it around 26.  So for me at least, I "trust" the Firstbeat/Garmin numbers a bit mroe than Runalyze in this instance.

  • I haven't delved into VO2Max and Trail Running specifically, but PC doesn't seem to adjust for much - it's a pretty raw calculation. VO2Max (which is calculated only at the end of a run) does take more into account.

    For example, in normal conditions, PC starts positive, and gradually declines, if it's too negative, I see a drop in VO2Max. If I do a hot run in summer, PC can be strongly negative (HR is much higher due to the heat), but the heat acclimation feature means I don't see a drop in VO2Max.

    Also, on a long run, PC will go negative as fatigue accumulates. But when the VO2Max calculation happens at the end, the watch says "Hey, that was a long run, and while you experienced fatigue, it was less than expected given the duration, so here, have a positive bump in VO2Max."

    So based on this, I wouldn't necessarily expect PC to reflect heavy trail conditions, even if VO2Max does. Or put another way, just because PC is negative, that doesn't mean VO2Max will be as well.