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.

The through-line here is that VO2 max is buzzy in the world of elite and recreational runners (and other athletes for that matter) alike — and for good reason. Not only is VO2 max a good indicator of your endurance performance, it’s also a marker of your overall health, according to Heather Milton, exercise physiologist supervisor at NYU Langone’s Sports Performance Center. In other words, this is a number to keep an eye on and strive to improve for the sake of your running performance and general wellbeing.

So, what’s the best way to calculate your VO2 max? And how can you improve it? We talked to Milton and other pros to bring you the answers to these questions and beyond — below.

“The higher your VO2 max, the more fit you are,” adds D Dr Dimitris Spathis, a visiting researcher at the University of Cambridge who recently developed a novel approach for estimating VO2 max using artificial intelligence (AI) models trained on raw sensor data from wearable devices. “Runners should know their VO2 max to understand their current fitness level and track improvements over time.” In fact, research shows that VO2 max and running economy are two of the main determinants of running performance.

Factors like age, gender, and even elevation can all play a role in your current VO2 max. So, too, can body composition, with more lean muscle mass typically meaning higher VO2 max. And resting heart rate is inversely related to VO2max: “Generally, the lower your resting heart rate, the higher your VO2 max,” Spathis says.

Lab Testing
Experts agree that a lab test, during which you run on a treadmill (or cycle on an exercise bike) donning a mask and incrementally increase your effort, is the “gold standard” for testing your VO2 max.

“In the lab, what we’re doing is measuring the oxygen you are breathing in and the carbon dioxide you’re breathing out, and that gives us that inference of what’s happening at the muscular level,” says Milton. Basically, when you cross over into not being able to use oxygen for energy anymore, that’s your anaerobic threshold or when you start to use your glycogen stores within your muscle, which means you will get very fatigued quickly. A VO2 max test helps to determine that threshold and therefore when your body stops turning to oxygen.

The downside here is that these tests can be expensive and inaccessible, says Spathis.

Wearables
Whether you’re team Apple Watch or Garmin, or prefer another brand or even a ring like Oura, most smart devices these days promise to predict your VO2 max — and they can, to some degree of accuracy. “If you’re looking at week to week, month to month, over the course of a year, you can absolutely use a watch to see progression of your fitness” and VO2 max, says Milton.

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. “There are some innate limitations in all of them,” she says.

If you look to data from the companies themselves, Apple published a whitepaper in 2021 that details research the company conducted to validate the watch’s VO2 max estimates. They had participants complete treadmill or cycle ergometer VO2 max tests while wearing Apple Watch, and concluded that the watch’s estimates are very close to the lab test, with slight deviations.

Meanwhile, the algorithms used by Garmin (from FirstBeat analytics, owned by Garmin) have been shown to be up to 95 percent accurate in past lab tests, according to the company.

“OURA recently announced a VO2 max feature, and the blog post was authored by Marco Altini, an experienced scientist in VO2 max estimation, so I am confident they are following proper protocols,” Spathis says. The blog acknowledges that this estimate is not as accurate as a lab test, but that users can “utilise this information to inform your current cardiorespiratory fitness and track how it changes over time.”

In short, use VO2 max data from your wearable to track trends over time rather than obsessing over a one-off estimate. And if it’s 100-percent accuracy you’re after, schedule a lab test.

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