A new study has quantified the accuracy of Garmin Vo2Max readings. It turns out they are not too far off the mark.

Anyone with a Garmin watch knows the device on their wrist has the ability to spit out a Vo2Max value. We won’t go too much into what this is. You can read our separate piece on this and the benefits of tracking the metric with wearables.

For the purposes of this article, let’s just say that Vo2Max is a measurement of how well your body uses oxygen when you’re working out at your hardest. It reflects the aerobic physical fitness of the individual, and is an important determinant of their endurance capacity during prolonged exercise. The higher your reading, the better.

Essential reading: Top fitness trackers and health gadgets

The best way to quantify your Vo2Max is by getting tested in a traditional lab setting. But this can be quite pricey and is not very convenient. Companies such as Garmin aim to simplify the process with fitness trackers and smartwatches. This makes the info accessible to all, it allows for more frequent readings and that type of info is used to prescribe exercise intensity.

To arrive at the estimate, Garmin starts off by combining info on your resting heart rate, age, gender, weight and other personal data. This is supplemented by information gathered during exercise analysing the relationship between your pace and heart rate. Properly defining your heart rate zones is important as speed data from “reliable” segments is used to calculate Vo2Max. On newer watches heart rate variability info is also used.

Here’s how Garmin groups the Vo2Max scores. The first table is for men, the second for women. Where do you fit in?

A new study published in the International Journal of Sports Medicine aims to quantify the accuracy of Garmin devices when it comes to estimating Vo2Max. For the research the scientists equipped 23 runners (11 male and 12 female) with a Forerunner 245 watch. This is one of Garmin’s more popular devices for runners.

The study participants visited the laboratory twice during the observation period to determine their Vo2Max during a treadmill ramp test. This information was compared with three outdoor runs where the metric was tracked by the Garmin watch.

So what do the results show?

The good news is that for runners that fall in the Vo2Max range between 44 mL/kg/min and 55 mL/kg/min, the mean absolute percentage error when validating against lab tests was just 4.1%. The criterion measure revealed a coefficient of variation of 3.5% in this range.

The bad news is that the results were less accurate (discrepancy of 7.1%) for runners with lower (below 45 mL/kg/min) or higher (above 55 mL/kg/min) Vo2Max. Which means these individuals should judge the Vo2Max value dished out by their Garmin watch with more caution.

On average, the Forerunner 245 showed an overall discrepancy of 5.7%. This leads to the conclusion that the watch can be used to track changes in Vo2Max. However, using this measurement to prescribe exercise intensity has limited application. This is because of the variations in accuracy that appear depending on the actual value of an individual’s reading.

These figures broadly correlate with other studies. Research from a few years ago used similar procedures to estimate the efficacy of the Garmin Forerunner 920XZ when it comes to dishing out Vo2Max values. They observed a 7.3% discrepancy against lab tests.

Another paper published in 2021 in the International Journal of Exercise Science utilised the Fenix 6S. This showed similar results.

Firstbeat Analytics, which is now under Garmin’s wing, also conducted a study. They monitored 79 individuals during 2690 runs over a 9 month period. Garmin’s Vo2Max estimates were compared with four lab tests. The results show that there was a 5% error on average (less than 3.5ml/kg/min) between the readings.

The caveat of that study was that the accuracy largely depended on how accurate a person has set their HRMax. If it is underestimated by 15 bpm, the Vo2Max error climbs to 9%. Overestimating by the same amount leads to a 7% error. So make sure you have this value set correctly.

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