Apple Watch Vo2 Max Accuracy, Tested: Is It Accurate?

Apple Watch VO2 max can be ascertained during an Outdoor Walk, Outdoor Run, or Hiking workout in the Workout app.

But, is Apple Watch VO2 max accurate? What is the VO2 max accuracy percentage or margin of error? Can you trust Apple Watch VO2 max to be accurate?

In this Apple Watch VO2 max accuracy guide, we will discuss how Apple Watch measures VO2 max and Apple Watch VO2 max accuracy according to testing.

We will cover: 

• How Does Apple Watch Measure VO2 Max?
• How Accurate Is Apple Watch VO2 Max
• How to Improve Apple Watch VO2 Max Accuracy

Let’s dive in!

How Does Apple Watch Measure VO2 Max?

Apple Watch VO2 estimates are considered a measure of your cardio fitness level, which you can then compare to others in your same age group and sex, as well as all ages and sexes when you navigate to the Health app on your iPhone.

Any Apple Watch Series 3 or later can estimate VO2 max.

The way that Apple Watch VO2 max recordings and estimations are captured and provided is by using the heart and motion sensors during an Outdoor Walk, Outdoor Run, or Hiking workout in the Workout app. 

Then, to estimate your VO2 max and cardio fitness level via Apple Watch, the Apple Watch considers this submaximal heart rate data in conjunction with your sex, age, weight, height, and any medications that may affect your heart rate that you have entered into the Apple Health app or your Apple Watch settings.

Note that you will not be able to get an Apple Watch VO2 max estimate right off the bat.

After an initial minimum of wearing your Apple Watch 24 hours, it still takes several reordered Outdoor Walk, Outdoor Run, or Hiking workouts and passive measurements with your Apple Watch for the first Apple Watch VO2 max estimate to be provided.

Apple considers VO2 max your “cardio fitness data.“ 

To find your VO2 max from Apple Watch workouts, follow the procedure below:

1. Open the Health app on your iPhone.
2. Tap Browse, then Heart, and then Cardio Fitness.
3. You can then tap D, W, or Y to view your average “Apple Watch cardio fitness level” for the Day, Week, or Year.
4. Your Apple Watch VO2 max scores will appear when you tap “Show All Cardio Fitness Levels.”
5. If you then tap on the VO2 max number presented, you can compare your Apple Watch VO2 max to the VO2 max for other fitness levels based on your age and sex.
6. There is also a “Show Information button” in the upper-right to view the average cardio fitness levels for all ages and sexes or Females and Males separately.

How Accurate Is Apple Watch VO2 Max?

So, is apple watch VO2 max accurate?

In order to understand Apple Watch VO2 max accuracy, we have to know what an accurate Apple Watch VO2 max means.

In other words, how is Apple Watch VO2 max accuracy determined? 

The accuracy of Apple Watch VO2 max, much like any fitness watch VO2 max scores such as Garmin VO2 max, refers to how closely associated the Apple Watch VO2 max score is relative to the true VO2 max value for the individual.

The gold standard VO2 max test is a graded exercise test performed in an exercise physiology lab or another setting where a metabolic cart is used to assess respiratory gasses and other physiological markers to help determine when the athlete’s true VO2 max has been reached.

Therefore, we use the specific VO2 max laboratory protocols to be a measure of the most accurate or true VO2 max.

So determining if Apple Watch VO2 max is accurate is a matter of comparing the Apple Watch VO2 max scores to the VO2 max scores for the same athlete achieved through the gold standard VO2 max laboratory exercise test.

Unfortunately, this is an interesting paradox because the main reason why the Apple Watch VO2 max capabilities are so valuable to everyday athletes is that the technology finally brings what was previously only available to elite athletes to recreational and competitive athletes training at home without access to a lab for true VO2 max testing.

While this helps the masses of everyday athletes have access to this valuable aerobic exercise training metric, it also means that on an individual basis, we won’t be able to readily test Apple Watch VO2 max accuracy with a head-to-head comparison of the Apple Watch VO2 max vs true VO2 max measured in a lab.

After all, most recreational runners or endurance athletes cannot get to an exercise physiology lab or afford VO2 max testing, let alone regularly.

Therefore, determining Apple Watch VO2 max accuracy can only be estimated or approximated based on individual case studies where a true T test—or head-to-head comparison of VO2 max values for the athlete—has been tested.

That said, while you likely won’t be able to access your own personal Apple Watch VO2 max accuracy, we can certainly look to the data collected from other individuals who have compared Apple Watch VO2 max vs. measured VO2 to get a sense of whether the Apple Watch VO2 max is accurate, or the percentage of error.

There have been very few if any, independent research studies that have tried to evaluate Apple Watch VO2 max accuracy.

However, most case studies have consistently found that the Apple Watch VO2 max scores consistently overestimate true VO2 max values.

These findings are consistent with a study that looked at Fitbit VO2 max accuracy.

The Fitbit Charge was consistent with VO2 max scores for an individual, but they were statistically significantly higher than lab-measured VO2 max for both men and women.

The average measured VO2 max was 49.91ml/kg/min vs Fitbit VO2 max of 52.53 ml/kg/min.

In fact, even a non-exercise VO2 max prediction equation was found to more accurately estimate VO2 max than the Fitbit VO2 max results relative to the true measured VO2 max for the subjects.

Fitbit VO2 max calculations use a similar process to estimate VO2 max as Apple Watch—using submaximal heart rate data to predict VO2 max.

This study also showed that Fitbit overestimated VO2 max values for both men and women.

Several factors can impact the accuracy of Apple Watch VO2 max measurements.

For one, the Apple Watch supports a VO2 max range of 14-65 mL/kg/min that is validated for users 20 years or older.

This means that any VO2 max score above this value will not be properly measured or presented; however, the good news here is that a VO2 max of 65 mL/kg/min would rate your aerobic fitness as “Elite,” which is the highest-ranking category for VO2 max standards.

That said, if you are in the “elite VO2 max category,“ you are likely still plenty invested in improving your VO2 max, as you will be a competitive athlete in your respective sport.

Therefore, being unable to accurately gauge improvements in your VO2 max through training will be understandably frustrating and is certainly a limitation of the Apple Watch VO2 max feature for highly-trained endurance athletes.

According to Apple documentation, “VO2 max estimation by Apple Watch is accurate and reliable relative to commonly used methods of measuring VO2 max, with an average error of less than 1 MET and an ICC of more than 0.85.”

Apple also reports that the Apple Watch VO2 is more reliable and consistent than submaximal treadmill testing, stating: “With test-retest reliability, VO2 max on Apple Watch has an ICC of 0.87 compared with 0.75 in submaximal treadmill testing.”

How to Improve Apple Watch VO2 Max Accuracy

The more Apple Watch outdoor workouts you accrue, the better Apple Watch VO2 max accuracy will become.

The Apple Watch will continually adjust your VO2 max estimate based on your changing workout data and passive recordings garnered while wearing your Apple Watch.

Here are some tips to improve Apple Watch VO2 max accuracy:

• Make sure the Apple Watch is tight around your wrist: Users suggest tightening the watch by one to two notches when you want to capture a VO2 max on Apple Watch workouts relative to how you wear the watch for general wear or casual workouts. 

This helps ensure that the wrist-based optical heart rate monitoring is as accurate as possible with little interference from the motion of the watch sliding or missed heartbeats due to the watch not sitting firmly against your skin.

• Pause your watch any time you take a break in a workout, such as stopping to use the bathroom or standing still at a traffic light before you can cross the street.
• Stop the watch when the main portion of your workout is over before you have begun a gentle cool down. Then, switch to the “cool down“ or Apple Watch walking workout settings.
• Ensure your biometrics are up-to-date on the Apple Watch or iPhone health app, mainly your current body weight, height, age, and biological sex.
• Recalibrate your Apple Watch periodically to ensure that VO2 max accuracy is as good as possible. You can learn how to recalibrate Apple Watch operations here.

One important thing to remember is that while the Apple Watch VO2 max may not be particularly accurate and is likely overestimating your actual VO2 max, you can still use your scores to inform your training by examining how it changes over time.

In other words, even if your Apple Watch VO2 max is inflated, since it does seem like the algorithm is consistent, you can trust improvements in your Apple Watch VO2 max score.

Ultimately, increasing your VO2 max is what matters most, not the exact number.

To learn more about how to improve your VO2 max, check out our article here.