How Accurate Is Garmin VO2 Max?

These days, Garmin GPS watches can provide workout stats that runners a couple of decades ago would have never imagined possible.

Besides basic running metrics such as your pace, distance, and time, many of the Garmin GPS running watches offer advanced data like your heart rate zones, vertical oscillation, stride length, and ground contact time. There are even more impressive analytics, such as a race predictor, lactate threshold, and VO2 max.

The Garmin VO2 max estimate can be quite helpful for distance runners, as VO2 max is arguably the best measurement of your aerobic capacity. Moreover, actually getting your VO2 max tested requires going to an exercise physiology laboratory, getting hooked up to a breathing mask, and running on a treadmill nearly to exhaustion.

But how accurate is Garmin VO2 max? Is the accuracy of Garmin VO2 max estimates decent enough to rely on what your watch reports?

In this article, we will delve into Garmin VO2 max accuracy and answer questions like, “How does Garmin measure VO2 max” and “How accurate is Garmin VO2 max?

We will cover: 

• What Is VO2 Max?

• Which Garmin Watches Have VO2 Max?

• How to Measure VO2 Max On a Garmin Watch

• How Does Garmin Calculate VO2 Max?

• Is Garmin VO2 Max Accurate?

• How Accurate is Garmin VO2 Max?

• Tips to Improve Garmin VO2 Max Accuracy

Let’s get started!

What Is VO2 Max?

VO2 max refers to the maximum volume of oxygen (in milliliters) you are able to use per minute per kilogram of body weight when running. 

Essentially, VO2 max is a number that encapsulates the maximum rate at which you can take in oxygen (through the respiratory system), transport it to muscles (via the circulatory system), extract it from the blood, and use it efficiently for aerobic energy production (via aerobic metabolic pathways in the mitochondria in muscles).

VO2 max is considered the gold standard measurement of your aerobic fitness, and there are established norms for VO2 max measurements based on age and sex.

These norms can help you assess how fit you are relative to the general population and elite athletes.

The higher your VO2 max, the better your aerobic fitness level and the more “highly trained” you are from an aerobic exercise standpoint.

VO2 max is modifiable through consistent training and workouts that challenge your cardiovascular fitness. Therefore, monitoring your VO2 max is a good way to keep tabs on improvements in your aerobic fitness.

Which Garmin Watches Have VO2 Max?

Although not an exhaustive list, the following Garmin watches have VO2 max: Garmin Forerunner 45, 55, 245, 745, and 945, all Garmin Fenix watches, and Garmin Vivoactive 4/Venu watches.

The owner’s manual for your particular Garmin watch model can tell you if your Garmin watch has VO2 max.

How to Measure VO2 Max On a Garmin Watch

On most Garmin running watches with VO2 capabilities, you can calculate your V02 max by navigating to the Run activity profile.

You must run for a minimum of 10 minutes (15 minutes for Vivosport watches), and your activity must be recorded outdoors where you have a consistent GPS signal.

Garmin VO2 max measurement also requires consistent heart rate data, but this can be from either a built-in optical heart rate sensor or from an ANT+-connected chest strap.

Also, in order for you to get a Garmin VO2 max calculation from your run, your heart rate must be elevated to at least 70% of your maximum heart rate without dropping below this intensity for a minimum of 10 minutes (15 minutes for Vivosport watches).

Some Garmin running watches have VO2 estimates under the Trail Running or Ultra Running activity profiles as well. Examples include the Garmin Enduro, Fenix 6, Fenix 7, and the Forerunner series starting with the 245 and above. 

Note that to improve the accuracy of Garmin VO2 max estimates, it’s important that you have accurate and updated personal info in your Garmin profile, including your sex, age, height, and weight.

VO2 max is measured relative to your body size, and comparisons are made based on age- and sex-matched peers, so this data must be correct.

How Does Garmin Calculate VO2 Max?

Before we can assess Garmin VO2 max accuracy, it’s important to understand how Garmin calculates VO2 max.

VO2 max on Garmin watches is calculated by evaluating the relationship between your pace and heart rate. The faster you can run at a relatively lower heart rate, the higher your Garmin VO2 max score will be.

Garmin captures speed data from reliable segments of your run (the segments are 20-30 seconds), and then this information is integrated into a formula for calculating VO2 max.

These VO2 max formulas calculate your theoretical VO2 max based on compiled VO2 max testing data from laboratory settings.

• For running on level ground, the VO2 max formula used is: Theoretical VO2 (ml/kg/min) = 3.5 x your running speed.

• For running on hilly terrain, the VO2 max formula used is: Theoretical VO2 (ml/kg/min) = 3.3 x your running speed + 15 x tan(inclination) x speed + 3.5.

Additionally, for Garmin VO2 max estimates, your effort level over different segments of the 10-minute data-capturing window is evaluated based on your heart rate during these segments relative to your heart rate zones (which are determined based on your user info).

Then, these assessments of your effort level are used to determine the theoretical VO2 you are working at as a percentage of your VO2 max. 

For example, if it’s determined that you are running 8 min/mile and working at 90% of your max effort level based on your maximum heart rate, the VO2 that correlates with that fitness level is 90% of your VO2 max.

From there, VO2 max can easily be calculated.

Is Garmin VO2 Max Accurate?

It’s crucial to establish that Garmin VO2 max estimates are simply that—estimates.

Calling back to what VO2 max actually is, it’s a measurement of how much oxygen you can take in and use efficiently and effectively at maximal effort.

This is why a standard laboratory testing for VO2 max involves wearing a breathing mask attached to tubes that analyze the composition of your inspired and expired respiratory gasses as you perform progressive running towards exhaustion.

A machine is precisely measuring how much oxygen you’re taking in relative to how much carbon dioxide you’re breathing out, as this shows your capacity to consume oxygen and use it while you run.

Your Garmin watch isn’t able to analyze the composition of your inspired and exhaled breaths.

Therefore, at a fundamental level, Garmin VO2 max isn’t measuring VO2 max.

The more runs you do with your Garman watch above that 70% maximum heart rate threshold for a continuous 10-15 minutes, the more accurate your Garmin VO2 max estimate will be. 

This is because the algorithm has more data to pull from, minimizing the effect of outliers and better capturing how your heart rate and speed trend together.

How Accurate Is Garmin VO2 Max?

Garmin’s Firstbeat Analytics is the unit of the Garmin company that developed and tested the Garmin VO2 max technology.

They conducted a study to measure Garmin VO2 max accuracy wherein they looked at the Garmin VO2 max estimates from 79 different runners over the course of a total of 2,690 for the group.

Each of the runners had previously had their VO2 max tested in a laboratory setting four times during a 6-9 month period. 

After comparing the Garmin VO2 max estimates with each runner’s laboratory values, results demonstrated that Garmin’s VO2 max estimation was 95% correct, with a margin of error of less than 3.5ml/kg/min (which is equal to 1 MET).

These results indicate that the accuracy of Garmin VO2 max is quite impressive.

However, there’s an important caveat here: the accuracy of your estimated maximum heart rate on your Garmin device will greatly affect the accuracy of your VO2 max estimate on your Garmin.

Evidence suggests that the Garmin VO2 accuracy drops to about 91% for runners who underestimate their maximum heart rate by 15 beats/min and 93% for runners who overestimate their maximum heart rate by 15 beats/min.

Therefore, it’s really important to try to have the most accurate number to use for your maximum heart rate.

A simple formula like 220 – your age will not suffice if you want to improve the accuracy of Garmin VO2 max estimates.

An independent research group also took on the question of how accurate is Garmin VO2 max by comparing the Garmin VO2 max estimate and a Polar watch VO2 max estimate to laboratory measurements.

Although the error for the Polar device was significant, the researchers found that the Garmin VO2 max estimate was highly accurate.

Although the Garmin VO2 max was consistently slightly higher than the actual measured VO2 max for men and women, this overestimation was not statistically nor clinically significant.

It was also less than the 3.5 ml/kg/min margin of error found by Firstbeat’s study.

Tips to Improve Garmin VO2 Max Accuracy

Although some of these points have been mentioned already, the following are useful tips to improve the accuracy of Garmin VO2 max estimates:

• Make sure your height, weight, age, and sex data in your profile are current and accurate.

• Measure your true maximum heart rate rather than using a formula to estimate it.

• Run more with your Garmin watch.

• Make sure you run where the GPS signal is clear and consistent the whole time.

• Wear a chest strap heart rate monitor because they tend to be more accurate.

• If you do rely solely on the optical heart rate sensing in your wristwatch, make sure the watch is appropriately tight, and your skin isn’t particularly wet.

How do you stack up to others with your VO2 max? Check out our comparative table on VO2 max averages based on age and sex.