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

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.

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.

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.