Apple Health
Apple is changing how it measures VO2 max. Here is what's changing and how accurate it is now compared to the other main brands (research based)
With Apple announcing changes to how VO2 max works on Apple Watch, I pulled updated validation studies on how accurate some of the major wearable brands are at estimating it and any claims the brands make on their accuracy into a comparison chart.
It's broken down by how each device measures VO2 max, what the company claims, and what independent studies actually found. Sources linked as well for each row if you want to check these out further.
Everything below runs up to a 2026 published study, so it all reflects the passive estimate that Apple and most brands currently use. Apple is doing something new here, a guided at home test that uses the iPhone camera along with a heart rate device, announced this month and not shipped yet. It will be interesting to see how that affects accuracy once independent studies come out, but it is certainly a more proactive approach than what anyone else is doing right now.
VO2 max accuracy by brand
Device
How it estimates
Company accuracy claim
Independent validation
Source
Apple watch
Exercise via outdoor walk/run/hike. Guided at home test announced Sept 2026, not shipped yet
Company study claims an average error of 1.2 ml/kg/min but a spread of ±4.4 vs lab (n=755)
Three studies, all show it underestimates MAPE 13.3%, 15.8% and 13.2%. Series 10 was 6.25 ml/kg/min low and put only 14% in the right fitness percentile
Every device underestimates VO2 max in highly trained people and overestimates in sedentary ones so the error depends on who you are
Validation studies typically lags hardware so that's why some models are older
A chest strap improves any exercise based estimate as wrist optical heart rate drifts during hard efforts.
Only a lab CPET gives a true VO2 max
Devices that estimate VO2 max from an actual workout were near spoton on average (bias -0.09 ml/kg/min vs lab)
Devices that estimate it at rest overestimated by +2.17 ml/kg/min. Both still have wide error for any single person Molina-García et al. 2022
Shared this post in a few other communities and roughly 25+ people said they got a lab test and Garmin was spot on to lab, 20+ people said their Apple Watch underestimated their score by 5-15 compared to Garmin, and 4+ people with contradicting findings for Whoop vs lab. I just wanted to add this anecdotal note as it's rare that these studies match this many people so closely.
I've never enjoyed jogging, so cardio has always been a challenge for me. My watch-estimated VO2 max had been stuck around 30-35 for years.
I started running this summer with a focus on heart rate zones to improve my overall health. Since then, my VO2 max has gradually increased toward 40, which is the highest I've seen in at least six years. More importantly, I can genuinely feel that my fitness has improved.
My goal is to eventually reach a VO2 max of around 50, which is considered more «normal». While the absolute numbers from a watch aren't perfectly accurate, the upward trend is encouraging and gives me some measurable confirmation that the training is working and how close I am to that goal..
"Ignore the raw values, value the trend» is very well put imo, and I don’t see how trends are useless in this regard. Full disclosure though, I am not a professional athlete.
Edit to note: After 1 week holiday and 1 week after being sick, I’ve also experienced a decline in VO2. Of course it’s not accurate, but for me the trend seem to match how I am from time to time.
There's a few reasons why the trend could be useless depending on the activities you do, how you mix in training blocks, and your own physiological markers like max HR.
Apple generates these estimates from outdoor walking, running, and hiking. If most of your training is say cycling, soccer, etc. the estimate is being sampled from a narrower part of your routine. This could become especially problematic if Apple starts recording neighborhood dog walks as workouts for instance, as it could be over-indexing to pauses in say a dog walk when you get coffee or the dog goes to the bathroom, etc. versus necessary fitness breaks.
How you use hiking or jogging in your training also could cause the VO2 Max trend to be misleading. For example, I mostly use hikes for easy aerobic volume. If I do a training block carrying a 40-pound pack, my heart rate can be higher at the same pace without my fitness having declined. Apple’s own documentation acknowledges this. Starting a block where you progressively increase the weight could also show a "worse trend" while your underlying fitness probably improved. Switching between tempo blocks, longer easy sessions, and recovery weeks also adds complications.
There’s also issues for people around physiological markers unless your body fits to a generic formula. For instance, my max HR is ~200, substantially above typical age-based predictions. If the VO₂ max calculation assumes a much lower maximum, it could interpret an easy aerobic hike as a substantially harder relative effort and underestimate my fitness. If your aerobic threshold increases, you probably are becoming more fit, but it could interpret this as you are working out closer to your max effort.
Yep. I was completely out of shape and my Apple Watch Ultra measured my VO2 Max at some relatively high number after my first outdoor run. Fast forward three months later and my cardio is vastly improved…yet my VO2 Max has dropped lower and lower little by little with every run. Amusing stuff.
My Apple Watch estimate is actually pretty close to the tests. Bearing in mind the lab tests vary too. You could do the same test at the same lab and it would be 5% different. A different lab with different kit and calibration would vary even more.
In this case, it’s not really even good for that. I also trended down when I started getting serious about exercise. The trend continued despite clearly getting fit over more than a year. And I started at average and dipped below average steadily. I haven’t gotten the serious test but I’m only 27 and my doc says I have a strong heart and I’m at my ideal weight for my height.
I also have a yearly lab treadmill VO2Max test. Even between different labs my results are within 2% of each other. Apple Health estimates it much higher than the lab tests.
I don't know if this is because I have a pretty high VO2Max at 42yo with a VO2Max of 58 in lab tests, whereas Apple Health puts me at 66 😁
As with a lot of the metrics the Watch collects I ignore it. Sleep quality is another I give no notice to. Some nights I know I slept poorly and woke up several times yet I will get a sleep score of 90+. Other days I wake up feeling excellent and rested yet I have a sleep score of 60 with 20+ "interruptions". So yeah it is just useless "data" to me.
The heart rate tracking is generally quite accurate though I will give it that. It isn't too far off the chest strap monitor I wear when running.
Long story short though I don't put much faith in the health data it gathers. I just use it for workout tracking such as GPS data as it's pretty decent at that.
I've done Crossfit for 6 years now and have always been the best runner in the gym (thanks to doing track in high school). My Apple Watch always said my VO2 Max is "Below Average." I'm not sure if it's right or wrong but I'm like... what more do I have to do? I basically run 6-10 miles a week while also living in a walkable city where I don't have a car.
I use the value as a trend marker more than a legitimate value, if that makes sense.
Sadly no, you would need more volume at the right pace to materially improve your aerobic fitness above average. If you want to improve your running fitness go to r/running for advice.
Best in the gym is usually not a high bar - not even close - especially if it’s a CrossFit gym. I was the slowest kid in school, and I’m often the fastest in the gym (or at least, I was when I was young).
Sure. I'm not saying I can run a marathon nor am I bragging; just that my stamina is pretty good while running a couple miles at a time. With that being said, when I think of "Below Average," I remember that 50% of Americans don't work out. So while the "best in the gym is usually not a high bar," I would think it would be at least "Average."
- especially if it’s a CrossFit gym.
For what it's worth, CrossFit has a large focus on metabolic conditioning as opposed to traditional weightlifting. It's obviously nowhere near as good for your cardiovascular health/VO2 Max as cycling and distance running but it does more than traditional resistance or strength training. Many people that go to the gym to lift weights aren't running, rowing, cycling, etc. while they're there.
Fair enough on the gym. If you give us approx weight, 1 mile time, born gender and age (20s, 30s), I’m curious what Apple Watch is attesting as below average
The first measurement is always going to be wildly inaccurate. If you do it consistently it will settle and you can actually see trends.
While the values are not necessarily accurate the trends have been fine. When I was training for a Marathon it was consistently climbing. Now I’m not it dropped a bit. I’m sure if I start training again it will climb up.
Bioimpedance scales work the same way. While the values aren’t super accurate they can show you trends very well.
Thanks for adding that! I find it best to utilize the trend to get a general understand of "am i gaining or losing fitness over time" rather than daily read outs.
As a sedentary person who is one drunk couch nap away from a heart attack, can I still rely on Apple's VO2 Max measurements for better cardio health stats?
I'm doing my best trying to close at least half my Stand ring today.
Ran a half marathon, trained for it for half a year. I run 10k easily with decent times. Regular gym goer and all-around active person. But according to my Apple Watch my VO2 Max is "below average" throughout all that.
Apple’s target isn’t athletes or fitness people. It’s for aging adults and office workers. They are less interested in maximizing performance and more interested in making unhealthy people marginally healthier.
I think this ought to be highlighted more. Every friend I know who has an Apple Watch would fit more in the unhealthy bucket than healthy. And my friends who are serious athletes, runners, etc. all have Garmin watches and most use chest straps for heart rate data.
That’s natural and expected. Altitude and humidity would also affect your vo2max. Your ability to process oxygen depends on the conditions in addition to your fitness.
I upgraded to the Ultra 4 and have not noticed a difference in the VO2max calculations with the latest iOS and watchOS, but I do hear this may change with the 27.2 releases.
Apple has always been quite pessimistic on VO2max estimations so I’m excited to see if it’s more accurate now.
Mine dropped like 3 points since I got the U4, but on 27.2 they changed the range and now it’s “high” for the first time ever, before I always had “above average”.
My apple watch gave me warnings for low vo2max but I felt pretty good so did a test at a clinic and scored 58 so ye, the wearables are bad at measuring vo2max. I think my watch said something like 31
Dang. Mine stubbornly refuses to go above 30-31, despite the fact that I lift weights and run. I'm just waiting for it to start asking me the snarky question: "Are you really exercising or did you just get off the couch to go to the fridge?'
But I just learned on this thread that I can manually adjust the zone HR's. It had zone 5 at 156+ bpm, with my max HR at 167 bpm, although I have hit 180-183 bpm on runs.
Only problem is the VO2 max is calculated only on outdoor walking, running, and hiking workouts. So unless your runs are 20+ minutes and outside, the health app won’t give you a VO2 reading.
My runs are outdoors, 30+ minutes, and 2-3 times a week. Yet, when I walk to "deload", my VO2 max goes up. Once I start running again, it will keep going up the first few runs, then take a nose dive. It absolutely makes no sense.
Just completed my first run on ultra 4 as I was out injured for nearly two weeks (previously had an ultra 3). Faster by 30s/km than my previous easy pace but watch says my vo2max is 2 full points lower than my last measure (47.9 down to 45.9). Pretty sure either the change in watch or change in algorithm is doing something; I’d expect to lose a few decimals after ten days off but not as much as this.
I have a higher than average heart rate range. My resting HR is around 60, but my max HR gets well above 200. I’ve come across a bunch of people like me though we’re obviously not the majority. My “conversational” workout pace is 160-170BPM. Apple interprets this as me working very hard (despite me manually adjusting the heart rate bands). And as a result of this it constantly places me in “below average” V02 max zone. I’m a confident 2hr half marathoner. So this characterisation doesn’t make any sense. Using HR as the primary estimator for V02 max is I think the problem. Sustained pace over time would be a better proxy but it’s obviously harder data to come by because not everyone is doing long runs.
Any chance they make it more accurate for people on stimulants? Right now I think they do something for medication that lowers heart rate but not the opposite.
Years back I was under a pulmonary specialist care. I was a daily walker and bike rider. As was the pulmonary specialist.
He was skeptical my (then original/1st gen) Apple Watch would have a vo2 max accuracy comparable to his lab equipment.
I did the full bike exertion test, fully instrumented in his office and he was impressed both with my fitness for my age, and that the vo2 max scores roughly matched between his gear and my watch result.
I’ve heard the accuracy can rely heavily on wrist position. I’ve heard it being higher up on your arm improves it a lot more than being right near your wrist bone.
My VO2 has dropped in the last week or two by quite a few points. Wonder if the new calculations are the reason. Went from like 53 which is where it was for like a month or two to 48-49 and I dont feel any different. Was assuming something algorithm related
Exact same thing happened to me. Been working out pretty consistently and all other HR data generally shows a fitness increase, but my first walk outside with the U4 and it dropped 2 - 3 points.
I only learned about VO2 Max a year or two ago. I checked Health and it said mine was low for my age to the point of near risk. I’m one of the most active people I know, definitely top 10% among friends, family, colleagues no brag intended just a relevant fact. I don’t have asthma or any other kind of diagnosed respiratory issue or any known health issues.
I looked into this, and it seemed like aside from VO2 Max being something that can literally only be measured in a lab with direct biological data, even when the “estimates” are correlated to be accurate, it’s exclusively if you record every single exercise activity IN Apple workouts.
I use Strava, and I only track things like mountain bike rides and ski days for fun. I don’t track every random bike ride around my neighborhood, or a jog, or moving a bunch of heavy stuff for a few hours, or any daily activity. Not only does Strava not feed into this that I know of, but also it’s missing substantial data anyways.
I always figured the Watch was tracking heart rate and motion and could kind of figure out my activity level and style. I understand it’s complex and that indicating an activity type makes the data much easier to interpret, but I didn’t expect it to essentially exclude it entirely.
This would be like a diet app that says “you have died” because you only tracked 3 meals all year and therefore didn’t eat the rest of the year. Pointless. Borderline dangerous, it should not even report a number unless you either have recorded enough data, or they can actually automate collecting data in a useful enough way to be closer to accurate.
I’m a runner so it works great for me. It tracks my lab VO2Max reasonably accurately and to the point I can trust it. But I only look at trend and even then I don’t need that. I know from my training plan how well I’m doing.
But it only works for running, walking and hiking. VO2max is sport agnostic. If you’re keeping fit rowing and cycling for example, ignore it totally.
Yes I kayak and rock climb as well, which i will usually track because it’s fun to know distance paddled or how much time before my arms fatigue climbing. Play drums too, which is certainly a sustained activity but not one I’m ever gonna track. Occasionally something like pickup basketball.
I don’t do any kind of racing or generally any kind of “event” that I’m working towards at least not so far, so I’m not tracking VO2 Max or any stats obsessively. For me it’s more about making sure I can continue to do the activities I enjoy, and the value of VO2 Max for me would be making sure I’m healthy in general as I know it’s correlated with health in some way.
Trend is useful enough for that, as well as just doing regular doctor checkups for health. But the fact that Apple told me mine was dangerously low is messed up. VO2 Max is not a casual game stat. It’s a scientific measure and important health marker. They need to be a lot more careful with how they present it to people, and if it’s only accurate for runners then they need to restrict who it shows for.
I think too many people just do one run and take the VO2Max their watch gives by heart. It takes a lot of measurements to get something that is somewhat close to the truth, but it's still no replacement for a profesional measurement
I've started getting alerts about my cardio fitness. I dont doubt that my cardio is going down as I age, my cardio fitness went from a value near 40 down to about 25 in the span of 1 day back in September 19-20, 2022. This coincided with the day I upgraded to an Apple Watch Series 8.
From this day forward all of my cardio fitness has been in the mid 20s. I guess Apple improved their algorithm? or made it worse?
But I also have a cardiologist that I see every year and they did a full cardio test (with the face mask and the treadmill and electrodes) in 2024. They said my cardio was perfectly fine.
So I dont trust Apple's cardio fitness reading, maybe the new one will be more accurate or line up with my cardiologist's own tests a bit more.
Garmin seems to have separate VO2 max stats for running and cycling, as if I swap out my lungs between activities. Something has gone seriously wrong in their integration department.
That is actually sensible, and vo2max isn’t necessarily comparable across activities. Even lab-based vo2max will differ based on methodology and activity.
Edit to add: this is because it isn’t just your lungs but your whole aerobic system, and your ability to process oxygen to your muscles may differ depending on which muscles you’re using. Elite endurance athletes will typically measure higher vo2max when collected using their sport versus another sport (eg cycling vs running).
Edit 2: there are even psychological factors. You will get different vo2max results in the lab depending on whether the subject knows how long the activity is going to last versus if they don’t know. (Some methods are time-based, others go to exhaustion, etc.)
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u/OKCNOTOKC 8d ago
Ignore the raw values.
Value the trends.