Garmin FR955 unreliable for running competitions

Thanks for your help! Except for a few moments, it's fairly accurate. Despite pulse measurement.

The reason I'm asking is that both VO2max and race predictions are quite dependent on correctly set max heart rate. (And the default age-based formula the watch uses is not accurate.) I was just thinking that could skew the race prediction.

Well, it was all on "automatic". But for now I removed sports running and added it again. Maybe it changes something?

I personally would suggest that you try to estimate your max heart rate yourself and enter the value manually. For example, my max heart rate would be 166 according to the 220-age formula (I'm 54). But in an unofficial max heart rate test, my max heart rate was 177 about 2 years ago, so probably 176 now (haven't had time to do the test again). That difference is huge and would have completely changed my VO2max estimate and race prediction. (For me, the race prediction from my Fenix 5+ is credible, as it's a little faster than I have raced those distances.) And if you allow the watch to set the max heart rate based on maximum measured heart rate during runs, it could be wrong in either distance (you don't reach your max heart rate in typical runs, and on the other hand an error in HR measurement could produce a too high value as well).

The method I used for my max heart rate testing was from Polar's blog: https://www.polar.com/blog/calculate-maximum-heart-rate-running/ (but there are many others as well).

My 965 and stryd race predictions for the half marathon are usually within 2 minutes of each other. I didn't know garmin was more dependent on the max hr like Bitti mentioned. I didn't mess with any settings in garmin, but maybe that's it.

Stryd does not care about your HR at all, it bases its predictions on your critical power.

Garmin, like basically all the other brands and platforms, estimates your performance based on VO2max, which itself is an estimate from the ratio between your HR (as a percentage of your maxHR) at a given pace. Thus, if you have set your maxHR too high or too low, the watch thinks you have too work easier or harder to maintain a given pace and the race predictions won't be accurate

My guess is that Max HR is one of the most important factors. I'm going to pin it to the most likely (measured last year in a test). I don't understand why it has been so extremely wrong since the switch to the FR955. I've been running with the FR955 since June 2022. And what I already mentioned, VO2Max has only changed 1 point, the predictions have really gotten worse and I'm not even talking about measuring sleep. But I'll leave that aside :-)

And yes, I am now also a big fan of Stryd because of its simplicity, accuracy and training plans. But I understand that you can't compare Stryd with all the possibilities that the FR955 offers. But I would expect Garmin to make their "flagship" of sports watches work accurately.

Race prediction is pretty good here... 10k within a minute, hm within a minute of the time I plan on runnig in 1.5 weeks (for a pr}, marathon within 3-4 minutes.

But yeah, it's all depending on proper heartrate aettings and measurements which can be tricky with the watch.

Btw, if you look at the vo2max in the training status widget you can see the more subtle changes (so it might not seem to change based on the rounded value, it might change in the background. 63.55 and 64.45 will show 64 for example)

Another place where you can see VO2max with decimals is to connect your Garmin account to Runalyze, and look at the VO2max there. (Although I don't know how useful it is to stare at the VO2max value too often, after all it's a number that isn't and shouldn't change quickly, and there's unevitably noise in the number, since it's inferred from other stats, not measured directly.)