How to Calculate VO2 Max

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.

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, C.S.C.S., 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.

In the simplest terms possible, your VO2 max is how much oxygen you’re taking in and the max rate at which you’re able to use it, Milton explains. Oxygen, which gets carried through your bloodstream to working muscles, helps them contract and relax, so it follows that the faster your body is able to use oxygen, the longer you’ll be able to maintain a faster pace.

“The higher your VO2 max, the more fit you are,” adds Dimitris Spathis, Ph.D., 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.

Here’s a breakdown of the primary ways to measure and keep tabs on this metric, ranked from most to least accurate:

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.

But because they’re relying on sensor data (like your heart rate at a certain running or walking pace as well as stats like your age, height, weight, and gender) 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. “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 “utilize 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.

Spathis’s team developed an AI model that can estimate VO2 max from wearables leveraging heart rate and movement data (like intensity levels) collected during activities like walking or even sleeping. He says this is unique compared to currently available wearables on the market because it doesn’t require GPS or for the user to complete any specific testing protocols (e.g. Oura Ring’s new feature has you complete a walking test). While this specific tech is not publicly available, it may be one day soon. In fact, one major watch developer has already expressed interest in Spathis’s team’s work.

Online VO2 Max Calculators

A quick Google search will reveal many options for quickly calculating your number by entering a few personal metrics, like your heart rate while walking, your gender, age, and weight. If only it were that simple! “These formulas have limited accuracy and don’t take advantage of the rich data captured by modern wearables,” says Spathis. “In our work we compared some of these formulas against ground truth VO2 max and we found they performed poorly.”

“The prediction equations aren’t really looking at [oxygen consumption], nor are they looking at finding what your peak heart rate is and all of those other variables that are good to know as well,” adds Milton.

Spathis also explains that these formulas don’t take into account how these variables (gender, age, weight, heart rate) interact with each other. “On the other hand, modern wearables use some sort of machine learning model trained on large populations. These models learn more complex relationships that explain better the variance of the underlying data,” he explains.

Milton says that for elite athletes, “anywhere between 60 to 80 ml per kg per minute is known to be a good VO2 max, and our targets for recreational athletes would be looking toward getting [them] in the lower end of that elite range.”

When asked for their number-one tip for increasing VO2 max, both Spathis and Milton provided similar answers: Mix up the intensity of your training! “There are so many people right now reading about zone 2 training and trying to stay in very low and steady heart rates, but we need to challenge ourselves enough to get adaptations and to improve our cardiac output,” Milton says, which means going into other heart rate zones, too.

“The best way to improve your VO2 max is through a mix of long slow distance and high-intensity interval training,” Spathis says. “Runners can generally expect some improvement in VO2 max after three to six months of dedicated training, with beginners seeing larger gains.”