Is my watch's VO2 max reading actually accurate?

Your watch estimates VO2 max from heart rate and movement data rather than actually measuring your oxygen intake, so it's not lab-accurate. Independent testing shows quality devices can be within about 6-7 ml/kg/min of lab values on average, which is close enough to track trends but not precise enough to obsess over exact numbers.

Why does my VO2 max change from day to day on my watch?

Single-day fluctuations can be caused by environmental factors like heat, altitude, fatigue, illness, or even incorrect resting heart rate measurements. The trend over several months matters far more than daily variations—track the direction rather than worrying about individual readings.

What's a good VO2 max number for my age?

It depends on your age and sex, but average sedentary adults typically sit in the 30s or 40s, whilst elite endurance athletes are often in the 60s or 70s. That said, comparing yourself to others is less useful than tracking your own trend—if your number is rising or holding steady as you age, that's what matters.

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The Number on Your Wrist: Making Sense of Estimated VO2 Max

Your watch estimates your aerobic fitness using heart rate and GPS, not actual breath analysis. Here's what that score really tells you—and what it leaves out.

1 November 20269 min read