How does Garmin Connect calculate VO2 Max?

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Sam Jelfs Jan 2021 3:49pm, 8 Jan 2021 856 posts	0 Sam Jelfs I think something might be going a little wrong in metric land
fetcheveryone Jan 2021 3:53pm, 8 Jan 2021 25,341 posts	0 fetcheveryone Fixed it Sam.
Sam Jelfs Jan 2021 3:53pm, 8 Jan 2021 857 posts	0 Sam Jelfs You're quicker than I could try a few things and write a feedback message :D
Sam Jelfs Jan 2021 3:54pm, 8 Jan 2021 858 posts	0 Sam Jelfs Oh and it matches what Garmin predicts for me.
larkim Jan 2021 3:54pm, 8 Jan 2021 13,137 posts	0 larkim VO2max (mL· kg−1 ·min−1)=58.687 + (7.520 × Gender; 0=woman and 1=man) + (4.334 × mph) − (0.211 × kg) − (0.148 × HR) − (0.107 × Age) I think is the formula in use based on the link in the blog. I can't critique the formula, but it doesn't seem to return a normal value for a flat out race. The biggest adjusting factor is the speed and the HR as a base calculation. Every 40-45s per mile pace difference would make 4.3 difference to the calc, but every 10bpm average would only change the outcome by about 1.5. Weight would constantly bring down the calc by 15.46 for me and age by about 5.1, and every 4.7kg in mass difference would make a difference of 1 to the overall calculation, every 9.35 years also make a difference of 1.
fetcheveryone Jan 2021 4:00pm, 8 Jan 2021 25,342 posts	0 fetcheveryone Larkim - I was thinking about the implication of the formula that weight gain would cause a drop in VO2max. The units of VO2max are mL/kg/min - so it kind of makes sense to me that if everything else remained constant, an increase in kg would reduce the value of VO2max.
Sigh Jan 2021 4:06pm, 8 Jan 2021 8,258 posts	0 Sigh My experience backs that up, Fetch. I was at my lightest last May, and my highest VO2 Max.
larkim Jan 2021 4:11pm, 8 Jan 2021 13,138 posts	0 larkim Yes, I suppose I can see that - same amount of O2 for an increasing mass reduces VO2Max in those units. But the correlation of maximal effort to VO2Max does seem to be fairly well agreed on, so I'm surprised there's such a gulf between the Vers and George paper and my figures. I don't think I'm a unique physical specimen 😉 But I'd have to weigh over 110kg to bring the calc in line for me as a 47yo-already-top-of-BMI-weighing-normal-HR-possessing runner over about a 10k distance.
SPR Jan 2021 4:22pm, 8 Jan 2021 32,879 posts	0 SPR If your weight changed, you'd run slower. VO2 max is per kg anyway which implies to maintain the same pace as weight increases you'd have to consume more oxygen. That's why I'm surprised that weight is a needed variable. Age basically the same, I can't obviously see from the formula what it's assuming via age but almost certainly it'll be some factor related to max HR and a assumed declining performance capacity as you age. I'll see if I can read the paper later.
larkim Jan 2021 4:24pm, 8 Jan 2021 13,139 posts	0 larkim For an experiment - 10k race, 38:30 time for a 40yo with HR average 175 (so in line with the wrong, but commonly quoted 220-age formula) weighing 70kg (11stone - not unusual?). Calc comes out at 63.3. That feels too high, doesn't it? Though I'm being unfair in that the calculator is intended to work for non-maximal efforts. The outcomes feel better at low effort figures. Still think it comes out too high for me, but then the paper itself presents its results as having a fairly wide band of outcomes. If I assumed my measured V02Max was close to the race derived figure (54.5 or so) then the graph suggests they'd have seen results in the range 47-58 or so, which is pretty wide. If I understood statistics I'm sure I'd be able to see some sort of standard deviation figure that validates that in their results - the graph is fairly clear though - above and below the formulaic predictions line there is a fairly constant spread.