Maybe your smartwatch has been telling you your VO2 max for a while now, but you’re not sure how accurate it is. Or maybe you’ve recently been targeted by social media ads for fancy running labs offering VO2 max testing complete with face masks and state-of-the-art treadmills. Or maybe you just saw that the Oura Ring launched a new “cardio capacity” a.k.a. VO2 max feature, and you’re curious how a little ring can generate such a metric.
But because they’re relying on sensor data rather than actual oxygen consumption like in the lab test, accuracy varies, especially when it comes to the more day-to-day changes, like if your device suddenly tells you you’re less fit today than you were yesterday, Milton says. Wearables also don’t typically account for environmental factors, like humidity, temperature, and even barometric pressure, which can be better controlled in a lab setting, per Milton.