Your Apple Watch Is Lying to you about your VO2 Max — Here's What a Real Test Costs and Where to Get One in the South Bay

Everyone's watch has an opinion about your VO2 max now. Garmin, WHOOP, Oura, Apple Watch — pull up the app and there it is, a number supposedly telling you how fit you are.

Turns out that number is mostly a guess.

Your watch doesn't, and physically cannot, measure VO2 max. Instead, it estimates it using your heart rate and your pace. A real VO2 max test measures the actual gas you're breathing in and out while you work at your cardiometabolic limit. Your watch has none of that ability; it's just pattern-matching.

How far off is the guess? One validation study on the Apple Watch Series 7 found a mean absolute percentage error of about 15.8% against real lab testing, which is significant. That's the difference between having an "average" VO2max and "poor".

Why does this matter? Isn't it good enough?

Depends on your goals. If you're training based on VO2max, you don't want to be comparing yourself to other people's numbers and sometimes making real decisions — like how hard to push a race — based on a guess that can be off by double digits. That said, tracking the relative number over time will give you a general idea if your maximum fitness is increasing or decreasing.

But if you want a number you can actually set zones from, compare to a real baseline, and retest after a block of training to see if something worked, the watch estimate isn't built for that job.

So what to do about it? Use the watch for the trend but get the real test for the baseline.

If you're in Los Angeles, we offer lab-grade VO2 max testing at the Movement Performance Institute in El Segundo both stand-alone and as part of our Activate Your Age longevity test. Contact us to find out more and book your test.