VO2 max has become the latest fitness metric getting a lot of attention among runners. The theory is that it’s an indicator of how efficient you are at burning aerobic energy – in other words, the higher your VO2 max, the better your running fitness. This new data point is being touted by running watch manufacturers like Polar, Garmin, and Apple Watch.

The best way to get a true reading of your best watch for vo2 max is by testing it directly in a lab, where you’re hooked up to a breathing machine that analyzes the composition of your inspired and expired air during progressive runs towards exhaustion. This can be expensive, and not everyone can afford to do it on a regular basis. This is why some smartwatch makers have started including VO2 max estimates on their devices.

Peak Performance on Your Wrist: Choosing the Perfect Watch for VO2 Max Optimization

Most of these estimates are based on heart rate data, with the more accurate the data, the more accurate the estimate will be. But wrist-based heart rate is only accurate to a certain degree, so there are other factors that can affect the accuracy of a VO2 max estimate as well, such as running surface, weather conditions (like heat and altitude), and other variables.

That’s why most experts recommend relying on chest strap heart rate monitoring when running for the most precise VO2 max estimates. This can ensure that you aren’t influenced by factors that can throw off the calculation.