[timanderson]

Experience of those race predictions varies! Mine are over-optimistic but not by that much, a friend is the other way round and Garmin continued to predict a slower time even when he actually recorded races in faster times.

[dpz]

I think its more potential, my 5k/10k are quite accurate but my half and full are quite off - which makes sense as they're the distances I train for. It also doesn't take other factors into account like running on track vs road

[rojeee]

That makes sense. If you do longer runs (and long fast runs) then your half/marathon time will be more accurate. In general, the issue with using VO2max to priduct race performance is that it doesn't take into account account running economy which is a massive factor in determining performance for longer distances. Same with lactate threshold, which has a big impact on all distances. E.g. at what point do you go from a metabolic steady state to an unsustainable state. It's the most important factor in distance running in my opinion. The threshold can be at quite a slow pace even for someone with a high VO2max if they are not doing the right training. E.g. think of someone who is excellent at HIIT and has a VO2max of 60+ but can't run a fast 10km.

[iamacyborg]

Pretty sure garmin do take other factors into account for their race predictions as they’ll update when your lactate threshold does, even if your vo2max remains the same.

[rojeee]

I think you are right regarding lactate threshold but im not sure how they factor in running economy as it's difficult to calculate. You need an accurate VO2 measurement. I guess they use HR as a proxy but in practise I find HR isn't such a good measure of metabolic output for various reasons; hills, unrelated stressors, heat, aerobic decoupling, etc.

[iamacyborg]

No one except elite athletes are looking at running economy, there are far too many confounding variables.

[rojeee]

Well.. a crude estimate of relative running economy is pace/heart rate and tracking it over time. Seeing the number go upwards means your economy is increasing and vice versa.

A fair amount of people track this because it's a feature of pretty much every training/coaching app.