Are Apple Watch cardio fitness readings reliable?

Having just updated to iOS 14.3 and watchOS 7.2, I saw the stuff about being able to check your cardio fitness levels in the Health app. I've had my series 4 watch for more than a year now, but the first cardio fitness data point I can see was recorded just 4 months ago. And in those 4 months, I’ve gone from being above average to low, with no data points in between. Nothing has changed in that time – since I got the watch I’ve been doing the same bike workouts at the same pace, and I feel the same; heart rate data has been stable. So I don’t understand why I don’t have any estimated VO2 max data points until a year after I bought the watch, and why the readings are all over the place. Anyone else had this issue?

I should say that I don’t use Apple’s Workout app – all my bike rides are logged with Strava.

Thanks.

Apple Watch Series 4, watchOS 7

Posted on Dec 15, 2020 3:19 AM

Top-ranking reply

RichardLim Author

Level 1

98 points

Posted on Apr 18, 2021 2:02 PM

As the originator of this thread, I can state that I've now solved my problem, although some might say I've cheated. My solution? Don't tell your iPhone that you're taking medication. It turns out that the reason my VO2 max reading fell off a cliff at some point was that I told my phone that I take one of the drugs that the Health app considers capable of affecting your heart rate. I am, in fact, on the lowest possible dose and I have been for years; most people would have been moved on to a higher dose quite early.

I suspected that entering the drug into the Health app some months ago might have triggered my low readings, so I eventually I tried deleting the drug. The very next VO2 max reading soared – suddenly, I was back into average territory. My fitness is not great, but I never expected it to be. I think I deserve to be average, not low.

One other thing I've noticed is that because I never used to log my walks with the Activity app, my Watch would try to do a VO2 max estimate once a week using any plausible walking data it could find. Because we've mostly been in lockdown, my walks have tended to involve going to and from neighbourhood shops, sometimes with a mask on and lugging groceries. In the past few weeks I've deliberately logged a few half-hour brisk walks without a mask and without carrying anything heavy, and my numbers are inching up all the time, as if the Watch is changing its opinion.

What I have I learned? Sharing your medication with your phone could lead to a huge VO2 max hit, even though your phone has no idea what dose you're on. And even if the VO2 max values are meant to be an estimate, they are crude because the algorithm might opportunistically scrape any activity data it can find, without knowing whether that was affected by carrying heavy gear or a gale-force head wind. Maybe Apple needs to add a setting such that only activities logged through the Activity app can generate VO2 max readings.

PS: I'll be happiest if and when Apple finally adds cycling to the list of activities that can generate VO2 max values, because cycling is 90% of my exercise. It ought to be possible to enter the weight of your bike and gear into the Activity app for a more refined estimate.

View in context

Are Apple Watch cardio fitness readings reliable?

Similar questions