How Polar Calculates Your VO2 Max (OwnIndex and Running Index)
Polar is the only major brand with two separate VO2 max systems, and they work in completely different ways. One asks you to lie down for five minutes. The other watches you run. Knowing which number you are looking at matters, because they are not equally trustworthy.
OwnIndex: a VO2 max estimate with no exercise
The Polar Fitness Test produces OwnIndex, a figure directly comparable to VO2 max, while you rest.
It combines your resting heart rate, heart rate variability, age, sex, height, weight and self-reported activity level. There is no exercise in it at all. The physiological reasoning is sound in outline: resting heart rate and HRV both track cardiovascular fitness, and the anthropometrics and activity level fill in the rest.
The appeal is obvious. No test, no suffering, a number in five minutes, and it works for people too unfit or too unwell to do a maximal test.
The catch is the accuracy. Non-exercise prediction models of this type land somewhere around 80 to 85% accuracy against laboratory treadmill testing in the general population, and they degrade at the edges. One study of masters basketball players found the OwnIndex test substantially overestimated VO2 max, with a mean error near 30% and poor agreement.
The self-reported activity level is part of why. You are grading your own homework, and the model takes your answer seriously.
Running Index: an estimate from every run
Running Index is not a test. It appears automatically after every run.
Polar takes your heart rate and speed during the run, together with your resting and maximum heart rates, estimates the maximal running speed you could hold on level ground, and converts that speed into a running VO2 max.
This is the same family of model as Garmin's Firstbeat engine, and it has the same strengths and the same weakness. It is based on what you actually did rather than what you said about yourself, which makes it the better of Polar's two numbers. But it rests on your maximum heart rate, and Polar still estimates that with 220 − age unless you have replaced it.
Estimated VO2max
42.4ml/kg/min
from the 12-minute Cooper test
Roughly where that sits
| Sedentary, about 30 to 40 | 30 to 40 ml/kg/min |
| Recreationally active, about 40 to 50Recommended | 40 to 50 ml/kg/min |
| Well trained, about 50 to 60 | 50 to 60 ml/kg/min |
| Endurance athlete, 60+ | 60+ ml/kg/min |
- This is a field estimate. A well-paced run on a flat course lands within a few points of a lab test, but pacing, terrain and weather all move the number.
- A true VO2max needs a laboratory gas-analysis test. Submaximal options include the Uth-Sorensen heart-rate method (VO2max is about 15.3 times HRmax divided by HRrest) and the Rockport one-mile walk test.
- Fitness categories vary by age and sex. Treat the band as a guide, not a hard line, and compare against your own previous tests over time.
A PDF of your personalized results, with a QR code to reopen them anytime.
Estimate yours from a race result and compare it against both Polar numbers. If OwnIndex is much higher than the other two, that is the expected direction of its error.
Which one to use
Use Running Index for tracking training. It moves with real efforts, it is grounded in performance data, and comparing it across similar runs gives you a usable trend.
Treat OwnIndex as a starting point. It is genuinely useful when someone cannot do a maximal test, and genuinely unreliable as a performance number for a trained athlete.
Fix your max heart rate first. Both systems use it. An estimate built on a formula guess inherits that guess.
FAQ
What is Polar OwnIndex? A VO2 max estimate from the Polar Fitness Test, calculated at rest from your resting heart rate, heart rate variability, age, sex, height, weight and self-reported activity level.
What is Polar Running Index? An automatic running VO2 max estimate produced after every run from your heart rate and speed, plus your resting and maximum heart rates.
Is Polar OwnIndex accurate? Non-exercise models of this kind run around 80 to 85% accuracy in general populations, and one study of masters athletes found it substantially overestimated VO2 max. Use it as an indicator, not a performance measure.
Why is my OwnIndex higher than my Running Index? Overestimation is the documented direction of OwnIndex's error, and the self-reported activity input pushes it the same way.
Which Polar number should I track? Running Index. It is based on what you actually ran rather than what you reported about yourself.
Other brands
- Garmin uses Firstbeat and short credible segments.
- Apple Watch has published independent validation.
- COROS uses a rolling six-week window.
- Fitbit also estimates from resting heart rate when you do not run with GPS.
Sources
- Polar on VO2max
- Polar on Running Index
- Polar Smart Coaching: Running Index
- How Polar calculates your max heart rate
Cover photo by Tristan Haskins, CC BY-SA 3.0, via Wikimedia Commons.
