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Comment by MPSimmons | Hacker News Reader

The Apple watch has a decent cardio fitness monitor. The absolute values aren't precise (since it uses VO2Max estimates, which is really only accurate if you're doing a metabolic stress test), but it's good to keep an eye on trends.

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I wonder how it estimates VO2Max and how often depending on the model. On my Series 3, it seems to make a data point two or three times a month and it’s concerning to me because it seems like it isn’t trending up even though I have started to do more cardio exercises. Instead, it has consistently reported a range that it says is below average.

Could it be that it’s just pretty difficult to improve VO2Max in general? Some people’s hearts have to beat harder or they breathe in less than fitter people?

VO2 Max is highly trainable, up to a point. But in order to see any significant improvement you're going to have to spend months consistently doing a mix of hard intervals and long zone 2 workouts.

There are major differences between individuals in terms of training response and achievable upper limit.

Series 5 does it post every Cardio exercise

According to Apple[0] it is only after the specific activities of: Outdoor Walk, Outdoor Run, and Hiking. Which explains why my estimated VO2 max goes down significantly in the winter months when I'm mainly doing cardio indoors and only taking leisurely walks with the dog outdoors.

[0] https://support.apple.com/en-us/108790#:~:text=Apple%20Watch....

I wonder why they can’t track cardio indoors. Perhaps because the watch doesn’t link up to most / any treadmills and is generally totally inaccurate with respect to distance and speed?

it's just the V02 max estimate which is only validated for those scenarios

That's correct, distance plays a role in the estimate somehow so they limit it to when they can verify via GPS. They don't seem confidant on their distance relative to running on a treadmill. I find my watch is pretty close to the treadmill readout most of the time except when I start getting tired and holding onto the handles, then it begins to diverge.

I have a mii band fit; it only calculates vo² max when you run for longer than 10 minutes reach a heart rate over 150

The FitBit vo2max estimate is fairly crude, at least for my model.

It requires a ten minute run on level ground at a certain heart rate to "calibrate" but tries to estimate it from other exercise too.

It leads to the number fluctuating quite a bit between runs and other exercises.

I'd argue that how you feel during a run or hard cardio training is a better metric. You can fairly easily judge progress week to week, completely subjectively.

I've also been wondering this. Mine reports a number that's way below what I get from other trackers.

I suspect it might use the age and gender predicted max heart rate in the calculations instead of the values set by the user in the workout settings. My MHR has been roughly 25 beats above the average throughout my adult life. As far as I know, above average MHR is not an indicator of poor cardio fitness in it self (even though being fit affects heart rate response).

The discussion part of this paper lists some causes for incorrect VO2MAX prediction, and has a line that may support my thesis https://www.apple.com/healthcare/docs/site/Using_Apple_Watch...

> In addition to chronotropic incompetence, other medical conditions can also decrease the accuracy of VO2 max estimates on Apple Watch ... medical conditions that severely limit exercise tolerance, preventing patients from reaching heart rates close to their predicted maximum heart rate

> I wonder how it estimates VO2Max and how often depending on the model. On my Series 3, it seems to make a data point two or three times a month and it’s concerning to me because it seems like it isn’t trending up even though I have started to do more cardio exercises.

The description in the Health App under Cardio Fitness (the one that shows VO2 Max) says that it measure it only for outdoor walks, hikes and runs. If you don’t do these outdoor activities, it won’t measure or record VO2 Max. I’ve seen this reflected in my measurements. I do HIIT and cardio workouts at home, and it certainly doesn’t measure or record VO2 Max.

Note that there's lots of complaints about the VO2Max estimates on Apple Watch. For example, this reddit thread:

https://old.reddit.com/r/AppleWatch/comments/m5q7yx/cardio_f...

https://old.reddit.com/r/AppleWatch/comments/yte3zd/the_vo2_...

Cardio still counts even if you don't measure it and share it with Apple.

Come on now. If it's not on Strava then it didn't happen.

Strava is not enough. You should make a tiktok livestream while exercising. Otherwise it's not a real workout

I think that Apple end-to-end encrypts fitness data.

Does Apple get your cardio data? It's my understanding is that is encrypted, even when it goes to iCloud for backup.

The poor VO2Max estimates on the Apple Watch is why I'm phasing out of wearing one.

I track my actual VO2Max measurements in Apple Health via a shortcut, and I don't need a daily made-up number messing up my data.

As the OP mentioned, absolute numbers are garbage, but trends are useful. Once a year just get an actual VO2Max test to peg the watch values too.

Where do you get a VO2Max test?

I just googled around and there were plenty of testing facility options in my metro area (Boston). Cost was reasonable too, typically less than <$100.

The trends aren’t really useful either unless you are recording strenuous exercise with the watch. I do a lot of cycling and my fitness in terms of how much power I can put out and for how long and my average heart rate for the same power has increased vastly, yet according to Apple my VO2 max has stayed consistent at around 45 for years since I only record walking exercises with it. I guess there’s not much it can tell if you only hit the mid 80s bpm at most during an exercise.

I realise it’s also another estimate but based on my cycling exercises Garmin is estimating my VO2 max at 55 and it does show a progression in my values.

The trends are garbage too. According to my watch my VO2Max has swung wildly between 55 and 45 over the last year, while every other measurement points to my fitness staying mostly steady.

Mine swings around as well, and I attribute it to the fact that Apple only uses Outdoor Walk, Outdoor Run, and Hiking to estimate VO2Max. Mine trends down in the winter months when most of my intense cardio is happening indoors on the treadmill or elliptical machine, and most of my outdoor activities are leisurely walks with the dog in poor conditions.

I find that my scores are mostly determined by how well I sleep the night before I do the workout.

Tracks with my numbers. I oscillate between 48 and 36, but my fitness is the same, I am just doing different activities.

I would love to see how this works. Where can I learn more? I’ve been pretty dissatisfied with the VO2Max on the watch overall.

You can create a shortcut that prompts you for text input, then appends the current datetime, and saves it to the health metric of your choice. You then export this to your home screen.

So when you get good data for your VO2Max (or anything else, really), you can easily save it and look at it on the Apple Health graphs.

The only way to get the Watch to stop messing it up with its daily hallucinated number is to turn off all fitness tracking (in the Privacy settings of all places).

But then half the reason for having the watch goes away.

How often do you do metabolic stress tests?

Why is Vo2Max important for people who aren't professional athletes? It's not that I'm not curious about my number I'm just not sure how helpful it is going to be - I need to understand what pace I can hold 5k, 10k, 21k and eventually 42k. I think the best way to know that is racing again and again and getting a good feel for your aerobic / threshold zone. Whether my Vo2max is 51 or 52 - does it matter to me?

To me it's a measurement of roughly how not-dead I am

Unless you're getting it tested in a lab, the number is not very accurate. Genetics also plays a large part in how much you can raise it.

For most casual people it's just a single data point that seems all encompassing so they go:

number goes up = good.

Most professional athletes don't really care about vo2 max all that much.

> looking at VO2 max in relation to all-cause mortality, we see a very clear trend. Simply bringing your VO2 max from ‘low’ (bottom 25th percentile) to ‘below average’ (25th to 50th percentile) is associated with a 50% reduction in all-cause mortality. When you go from ‘low’ to ‘above average’ (50th to 75th percentile) the risk reduction is closer to 70%!

https://peterattiamd.com/category/exercise/vo2-max/

But isn't it one of those things where someone with a higher VO2 is likely doing healthy things that they have lower risk. Rather than a lower risk simply because their VO2 is higher.

I've been seeing strange downtrends on my VO2Max numbers with Apple Watch: they have dropped from 40's to 20's over a matter of a few days and have been steadily trending down. I haven't changed my exercise patterns at all for years now. There are others on the Apple forum facing similar abrupt drops, anyone else here seeing it? I'm hoping it's the watch messing up and not my health!

I love my Garmin Fenix 6 pro.

VO2 max is also exercise dependent. If you trained riding bike for 3 months, then went to run down the street, your VO2 max would not transfer over.

Is that true? Back when I was a crew gremlin, my VO2 max as measured via erging was off the charts. But I could apply that cardio capacity to things like running/biking/swimming pretty effectively.

It's true in the sense that you'll be better optimized towards the activities you train in most intensely in regularly, but you do develop transferable gains as well. It's just not 100% transferable.

I think the GP's comment is just easy to misread.

There's famous studies about people testing VO2 max with one leg trained exercises,then looking at VO2 max with non-trained leg.

https://onlinelibrary.wiley.com/doi/10.1111/j.1748-1716.1976...

That's why there are separate Cycling and Running VO2 indicators

You won't be a 55 Vo2 runner if you're a 55 Vo2 Cyclist, but cardiovascular fitness does cross between those activities to an extent

Your indicators will be different, but your actual O2 uptake should be essentially similar. Any difference should be due to technique (if you've optimized your breathing/rhythm/etc for one but not the other).

This is incorrect. VO2max is influenced mostly by muscle recruitment - different muscle group trained would be a hindrance if anything

"VO2max is influenced mostly by muscle recruitment"

This is incorrect - the primary factor is heart and lung function. Yes, muscle training can play a factor, but is relatively minor compared to that.

Lung capacity is genetic and heart is only trainable up to a small limit bc there’s a layer of fascia around it preventing further expansion. That’s the “supply” side of vo2. The “demand” side is the recruitment and efficiencies you’ve developed which are exercise dependent. This is why you dont see a lot of cross training (except for recovery) and a lot of z4 work in the professional training programs

VO2 max is a measure of oxygen uptake and distribution. Your VO2 max will transfer over. However, if you're measuring VO2 max in some ancillary way (not a stress test machine) then it will appear differently since you're level of effort will vary based on your technique dor the chosen exercises.

My VO2 max from running definitely transfers to cycling. Doesn't mean I'm an amazing cyclist but at least cardio isn't my limiting factor.

It transfers to an extent. Lance Armstrong marathon PR is 3 hours from what I read, which is a great result for an amateur runner but totally unimpressive for a professional endurance athlete, let alone one of the best in history. I was actually a bit surprised that's the fastest Lance could do and to me it shows it doesn't cross over that well.

Not surprising at all. Vo2 in general is not great metric for elites and specificity is king. Which is why you rarely ever see elites cross train much

I wonder if running crosses better to cycling than vice versa, I think it might cross a bit better because running involves more (pretty much all) muscle groups. On the other hand there might be a lot of technique in cycling that takes a while to learn so idk.

Running down the street at top speed, i.e. for a minute or so, is an anaerobic activity.

Even sprinting 100m takes 60% ! energy from aerobic system.

But do you really need a botnet on your arm to get motivated to do sports once a week? Weird society

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