I Took a $200 VO2 Max Test. How It Compared to My Apple Watch’s Score.

One statistic the Apple Watch tracks is an estimate of my VO2 max, the maximum amount of oxygen consumed during intense exercise. Many health experts consider it the single best indicator of cardiorespiratory fitness, and research has found that it correlates to longevity as well. In fact, the American Heart Association says fitness level should be considered a vital sign.

VO2 max is measured in milliliters of oxygen a minute per kilogram of body weight. To know your true number, you have to exercise intensely while wearing a mask that measures oxygen consumption. The more oxygen you burn, the fitter you are.

The Apple Watch, of course, doesn’t include an oxygen mask. Instead, it looks at heart rate, weight, age, other personal information, and walking or running speed to make an estimate of VO2 max. My watch tells me I have a VO2 max of 39.4, which it says is high for a 66-year-old man. Higher is better for this score, so that sounds good to me.

A resting person consumes 3.5 milliliters of oxygen per kilogram, which is called a MET. According to my Apple Watch score, I am capable of burning nearly 11.2 times that amount, or 11.2 METs. The more you can burn, the better your fitness. Apple says its estimates are accurate on average within one MET.

I should have stopped there, but I didn’t. I wanted to test out the Apple Watch’s accuracy. So I took an actual VO2 max test at a local sports medicine center for $200. No, insurance didn’t cover it.

The woman administering the test attached EKG clips to my chest, put a mask over my face, and told me to walk on a treadmill. She gradually increased the speed to five miles an hour, and then she began increasing the incline. I lasted 11 minutes, until it was at a 12% slope. I could have gone another minute if I really needed to, but it was getting hard. My legs still felt tired hours later.

I thought I had done well. True confession: Vain man that I am, I also was hoping my measured VO2 max would be even better than Apple’s estimated score.

But the test isn’t just measuring effort, it is measuring how high your oxygen consumption goes before it plateaus. Mine stopped rising at 34.6 milliliters per kilogram of weight, below the 39.4 score estimated by my watch.  

Whereas I was hoping my Apple Watch had underestimated my fitness, it had actually overestimated it by roughly 1.3 METs. That is a bit more than the average error cited by Apple, but still in the ballpark.

Bottom line: My fitness level is above average, but it’s nothing stellar either. According to the Marathoner handbook table, I’m in the 75^th percentile for my age. That means I’m in good health (knock on wood), but my fitness is way below the levels of a competitive endurance athlete my age. 

Oh, well. Easy come, easy go.

Write to Neal Templin at [email protected]