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Race predictions way off

I have switched from Forerunner 245 to Forerunner 965 recently (yes, Christmas present :)). On the day that I switched, the race predictions dropped enormously. Now, ten days later, the predictions are still way off, they are worse than all my PR's.

Does the Forerunner 965 use a different algorithm than the 245? And why does a newer model show worse predictions?

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S.M.R. over 1 year ago +1

In my view - and recollection - the calculations were changed on the FW a while back (More than a year ago at least on the 955 if I recall - can't see it on the graphs now as they only go out a year) and…
Etupes25 over 1 year ago +1

peterdb said:
On the day that I switched, the race predictions dropped enormously

The first suspect is your HR Max value. Your new watch can estimate your HR Max based on your training history. The accuracy…
Etupes25 over 1 year ago in reply to FlowState +1

FlowState said:
I changed the manual value to be 50 beats lower and saw no immediate change in my VO2 Max or race predictions.

Obviously, you have to get a new VO2 Max value: just changing the HR Max value…

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0 Etupes25 over 1 year ago in reply to FlowState

I found some information about the algorithm that could be used here.

As you can see in the article and patent, weight is not a parameter

Only age is an input, for the purpose of deriving the HR Max based on 210-0.65age formula.

According to the Firstbeat patent, the VO2 formulas are based on pace, power and gradient depending on the activity. Again, the key of the algorithm is to select qualifying data, then applying formulas.

"Walking and Pole Walking: Theoretical VO2 (ml/kg/min)=1.78*speed*16.67[tan(inclination)+0.073]
Running on a Level Ground: Theoretical VO2 (ml/kg/min)=3.5 speed
Running in a Hilly Terrain: Theoretical VO2 (ml/kg/min)=3.33*speed+15*tan(inclination)*speed+3.5
Cycling: Theoretical VO2 (ml/kg/min)=(12.35*Power+300)/person’s weight
Rowing (Indoor): Theoretical VO2 (ml/kg/min)=(14.72*Power+250.39)/person’s weight Unit of speed=kilometers per hour (km/h)
Unit of inclination=degrees)(°)
Unit of power=watts (W)
Unit of weight=kilograms (kg)"

https://sites.udel.edu/coe-engex/2019/03/16/how-accurate-is-your-garmins-vo2max-estimate/

The HRV minimum tis then used o calculate VO2 Max and HR Max from VO2 at HRV minimum.

"Of course, it is possible to estimate person's HRmax based on person's exercise induced HRV response only. Minimum value of HRV is usually reached at about 75-85% of HRmax (respiratory compensation threshold, RCT), and therefore HRmax≈HR_at_RCT/0.80. Similarly when RCT is expressed as % VO2max it is usually reached at about 70-80% VO2max and therefore VO2max≈VO2_at_RCT/0.75."

https://patents.google.com/patent/US20110040193A1/en

0 Bitti over 1 year ago in reply to Etupes25

I'm hesitant to chime in (since there are already soooo many people in this guessgame), but oh well: I have a feeling that the reason weight is so confusing here is because it as cancelled out in the calculations.

To get the relative VO2max (ml/kg/min) from absolute VO2max you need to know the weight. But in the calculation of absolute VO2max you need power (to estimate energy consumption which causes the oxygen consumption). And the power is derived (among other things) from pace. And that calculation from pace to power also depends on weight (the more you weight, the more power you need to produce for the same pace).

So, since both of those dependencies on weight are more or less linear, they cancel each other out and you don't actually need to know the weight to get from HR + pace to relative VO2max (pace to power requires multiplying by weight, from absolute VO2max to relative VO2max requires dividing by weight).