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How the hell is VO2-max actually calculated with the AW?

S

Spindel

macrumors 6502a
Original poster
Oct 5, 2020
521
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OK OK hear me out (since I know there are a fair share of VO2-max threads being made on this forum).

I fully understand that the presented absolute value from AW should be taken with a grain of salt. But I have used it more as a relative value tracking my progress (as in watching it increase with my exercise over time).

But today I became really puzzled. I just finished a run (8,73 km) and by every quantitive and subjective metric except one this run both felt better and was better than my previous run of 8,5 km a couple of days ago. And still the estimated VO2-max value calculated dropped by 1 compared to the previous run. A small variability down or the same value as the previous run wouldn't have really bothered me but a drop of 1 was a bit steep, also if I look at the general trend I've had for the last year.

The only metric in this run that was a bit "worse" compared to the previous run was my heart rate. This time around my average heart rate was 171 bpm (170 bpm on the previous run) and max heart rate was 182 bpm (180 bpm on the previous run). But this was very much a product of my daily shape being a bit better today and the weather a bit colder so I could push my self a wee little bit harder (with also resulted in a bit higher cadence and a better overall time).

It just feels backwards that I get a significant drop in VO2-max when everything both felt better and was better except for a very slight increase in heart rate.

DISCLAIMER
Before people jump on me to seek out a doctor about my heart rate being high I can assure you I'm perfectly healthy and have no problems. This is normal for me when exercising (when it's not too warm, under warm conditions I have a hard time pushing beyond an average heart rate of 155 bpm) and just how I'm wired. Resting heart rate is fairly low etc it's just that I (as long as I'm not ill) feel no adverse effects of straining myself to high heart rates over extended periods of time.
 
StumpyBloke said:
I don’t know how it is calculated on my series 6, but since installing watchOS 8 beta my readings have dropped by 3% instantly. In my opinion it is absolute garbage and not worth anything.
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Sounds like the strange jump I got when installing WOS 7.2 got fixed :p

Made a thread about it doing a significant jump here: https://forums.macrumors.com/threads/watchos-changed-vo2-max-algorithm.2275537/

But this that I talk about in the OP is not the same since I have not done any update etc between todays run and my previous run. And even if the absolute value has always been questionable the trend I've had has felt fair. Just todays drop that puzzled me.
 
Spindel said:
But today I became really puzzled. I just finished a run (8,73 km) and by every quantitive and subjective metric except one this run both felt better and was better than my previous run of 8,5 km a couple of days ago. And still the estimated VO2-max value calculated dropped by 1 compared to the previous run. A small variability down or the same value as the previous run wouldn't have really bothered me but a drop of 1 was a bit steep, also if I look at the general trend I've had for the last year.
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I know you said you know to take the figure with a grain of salt, but do remember it's an estimated figure based on indirect measurements. As such, the occasional outlier is to be expected.

Just my opinion but I would ignore a single reading that's at variance to your prior trend.

BTW - check out https://www.apple.com/healthcare/do...h_to_Estimate_Cardio_Fitness_with_VO2_max.pdf
 
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I also noticed unexpected changes in VO2max. When I pushed myself beyond the max exercising heart rate for my age, my calculated VO2max was below average. When I started keeping my heart rate below the recommended max, my VO2max went to above average. Perhaps your higher heart rate implies you have to pump more blood for a given activity, thus implying you are not transferring O2 as efficiently. Only a guess since the equation used is a mystery.
 
deeddawg said:
I know you said you know to take the figure with a grain of salt, but do remember it's an estimated figure based on indirect measurements. As such, the occasional outlier is to be expected.

Just my opinion but I would ignore a single reading that's at variance to your prior trend.

BTW - check out https://www.apple.com/healthcare/do...h_to_Estimate_Cardio_Fitness_with_VO2_max.pdf
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That document actually explain pretty well how the AW is calculating VO2-max.


Thirio2 said:
I also noticed unexpected changes in VO2max. When I pushed myself beyond the max exercising heart rate for my age, my calculated VO2max was below average. When I started keeping my heart rate below the recommended max, my VO2max went to above average. Perhaps your higher heart rate implies you have to pump more blood for a given activity, thus implying you are not transferring O2 as efficiently. Only a guess since the equation used is a mystery.
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So if I was to run slow and keeping my heart rate down I probably would get an increase in reading of VO2 max by the apple watch. Still if I where to run at the recommended heart rate range for my age it wouldn't feel like exercise for me. I mean as it is now I'm tired after finishing my run, but not that tired and I bounce back really quick. But then again this should only impact the absolute value and does not explain the drop I observed in a run that, as I said, by every metric felt better than the previous run.
 
Spindel said:
That document actually explain pretty well how the AW is calculating VO2-max.




So if I was to run slow and keeping my heart rate down I probably would get an increase in reading of VO2 max by the apple watch. Still if I where to run at the recommended heart rate range for my age it wouldn't feel like exercise for me. I mean as it is now I'm tired after finishing my run, but not that tired and I bounce back really quick. But then again this should only impact the absolute value and does not explain the drop I observed in a run that, as I said, by every metric felt better than the previous run.
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Would you use your height to find what shoe size to buy based on the average shoe size for people your height?

No? So why use your age to come up with your maxHR and HR ranges?

The various formulas using age are giving the population averages and ignore individual variance.

To find *your* maxHR and thus your appropriate HR ranges you're gonna need to sweat a bit. Go all out at the end of a 5K race. Find a hill near the end of your next run and push up it until you're nearly ready to hurl. (of course, get clearance from your doctor if you're not already regularly active or have any concerns)

Then with your estimated HRmax and your measured resting HR (HRrest), check out the Karvonen formula/method for using Heart Rate Reserve to estimate your HR training zones. More info here (not an endorsement for the site, just one I found for you to have more info): https://runandbeyond.com/karvonen-heart-rate/

Couple of decent articles:

Maximum Heart Rate - How to Find it.

Maximum Heart Rate and Running - Tips on How to Find it. The Max test, Sub-max and Formulas
www.marathon-training-schedule.com www.marathon-training-schedule.com
 
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I find that as long as you let it settle, it reflects your current health situation - whether or not it was an accurate V02 Max reading, I have no idea - I just know it goes up and down based on my ability to run miles faster/slower depending on my health/fitness level - and it does that fairly well.

Late last year (November 2020) I had a health event that dropped my V02 Max from 46 to 34. I was out for a month - unable to exercise, unable to sleep, etc. It has taken me most of this year to get back up to a 40 V02 Max. I went from a 11 min mile to barely being able to jog 16 min miles without stopping constantly. Over this year I've gotten it back down to 12 minutes - I've run 178 miles this year to date. (I am not a small person (230 pounds - 5'11)).

So <shrug> lol. I'm not a health nut or runner so just observations from my life. I hope to get it back up to 46 by end of this year! :D
 
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Spindel said:
This time around my average heart rate was 171 bpm (170 bpm on the previous run) and max heart rate was 182 bpm (180 bpm on the previous run).
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The problem with a 180 b/m heart rate is that, for some reason, you are losing pumping (stroke) volume with a rate that high -- too short a myocardial repolarization time? -- , then compensating for that through an increased heart rate. You may have an physiological anomaly, but you might also have a pumping and/or coronary arterial perfusion problem. Seeing a cardiologist might be a good idea; "perfectly healthy", or not. Better to be safe.
 
Mine has calculated VO2 max exactly 3 times in 2 years. Not sure what the deal is.
 
Spindel said:
Just for the record I have never used the breathe app and I get VO2 max value from every run or walk i register.
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Same, I never use the breathe app either. lol. I get a VO2 Max reading every time I put in a good run of at least a mile.
 
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