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Can Your Garmin Accurately Measure Your VO2 Max?

By Jiri Kaloc

Getting your VO2 max measured requires expensive laboratory equipment and it’s not really cheap or convenient to do it often. Garmin promises to estimate your VO2 max just by having you wear a watch while exercising. How accurate are Garmin devices when it comes to VO2 max?

VO2 max measures your fitness

VO2 max tells you how well your body uses oxygen during exercise. It’s a measure of aerobic fitness and endurance capacity. The higher VO2 max you have, the better. Just for reference, most Tour de France riders have a VO2 max above 70 ml/min/kg and general classification winners have above 80 ml/min/kg. Untrained people would measure at between 25-35 ml/min/kg, but seasoned amateur cyclists could push their VO2 max into the high 50s. If you want to know what a good VO2 max for your age and gender is, you can check out Garmin’s spread sheet here.

How does Garmin measure your VO2 max?

Garmin devices allow you to have your VO2 max measured frequently and for no extra cost. Garmin’s partner, Firstbeat Analytics, developed a method for estimating VO2 max just using data from your watch. Your Garmin combines several stats that it directly measures, or asks you to input.

  • Pace and heart rate during exercise
  • Resting heart rate
  • Heart rate variability
  • Age
  • Gender
  • Weight

Scientists test Garmin device accuracy

With every new feature from a smartwatch, it’s natural to wonder how accurate and reliable it is. Researchers from the University of Würzburg, Germany decided to answer that question by putting the Garmin Forerunner 245 to the test against gold-standard laboratory equipment. They recruited 23 runners (11 male, 12 female) and determined their VO2 max in the lab during a treadmill ramp test. They compared this info with three outdoor runs, where VO2 max was tracked by the Garmin watch.

Garmin was 5.7% off

The study found that overall the Garmin Forerunner 245 was off by 5.7% when compared to laboratory measurements. The watch was more accurate in runners who had a VO2 max in the range of 44 – 55 ml/min/kg, with an error of only 4.1%. For runners below or above these values the discrepancy was higher. The study shows that the Garmin watch is accurate enough to track changes in VO2 max. But it might not be accurate enough to prescribe exercise intensity based on the VO2 max measurement.

The results of this new study are very similar to past research. A study that looked at the Garmin Forerunner 920XZ showed a 7.3% discrepancy against lab tests. Another study that used the Garmin Fenix 6S watch also found similar numbers. Firstbeat Analytics conducted their own study and found a 5% error, which was equivalent to 3.5 ml/min/kg.

Make sure to input accurate HRMax

The one thing we know from these studies is that the accuracy depends a lot on how accurate a person sets their max heart rate value HRMax into the watch. Underestimating by 15 bpm results in the VO2 max error reaching 9%, and overestimating by 15 bpm leads to a 7% error. So, if you want the most accurate VO2 max measurement from your Garmin, make sure to do an accurate maximal heart rate test and use that value to define your heart rate zones in your Garmin settings.