How Suunto Calculates Your VO2 Max (Fitness Level)

Suunto calls it Fitness Level rather than VO2 max, and the engine behind it is not Suunto's. It is Firstbeat Analytics, the same company whose algorithms produce Garmin's VO2 max estimate.

So if you have ever wondered why your Suunto and a friend's Garmin produce suspiciously similar numbers, that is why.

What Firstbeat does with your data

The model compares your external workload, your speed from GPS, against your internal workload, your heart rate as a percentage of your maximum. At a given pace, a fitter person's heart rate is lower, and the size of that gap is what the algorithm converts into an oxygen uptake estimate.

Firstbeat does not use a whole activity. It looks for short segments where the data is trustworthy: steady movement, no stopping, clean GPS, and a heart rate high enough to be informative.

The Suunto implementation covers running and walking, and it is available on the Suunto 3, 5, 5 Peak, 9, 9 Baro, 9 Peak and 9 Peak Pro. If your model is not on that list, the feature is not there to find.

The number it depends on

Heart rate enters the model as a percentage of your maximum, which means the whole estimate is built on top of that setting.

Suunto defaults your maximum to 220 − age, the least accurate formula still in circulation, carrying an individual error of roughly ±10 to 12 bpm. If yours is eight beats too high, every run looks easier than it was, and the Fitness Level comes back higher than you have earned. Too low and it comes back short.

Fixing that one field is the highest-value thing you can do to the estimate, and it takes two minutes.

Estimate yours from a race result or a field test and compare. A gap of more than a few points usually points at the max heart rate setting rather than at your fitness.

Getting a trend you can read

Firstbeat-based estimates are far better at direction than at absolute value. Keep the inputs constant and the direction becomes meaningful:

• Use a chest strap where you can. Optical wrist heart rate is the larger source of error in this kind of model.
• Feed it steady running. Intervals, technical trail and heavy hills produce fewer usable segments and distort the pace-to-heart-rate relationship.
• Compare like with like. Judge the trend across similar runs on similar ground rather than across everything you have done.

FAQ

How does Suunto calculate VO2 max? Through Firstbeat Analytics, by modelling your GPS speed against your heart rate as a percentage of your maximum, during running and walking.

What is Fitness Level on a Suunto? Suunto's label for its VO2 max estimate.

Which Suunto watches have VO2 max? The Firstbeat fitness level feature is documented on the Suunto 3, 5, 5 Peak, 9, 9 Baro, 9 Peak and 9 Peak Pro.

Why is my Suunto VO2 max wrong? Most often because the max heart rate in your profile is still the 220 − age default. The estimate is a function of that number.

Is Suunto's VO2 max the same as Garmin's? Both come from Firstbeat, so the underlying approach is the same. Implementation details and your heart rate settings still make the numbers differ.

Other brands

• Garmin uses the same Firstbeat engine, with cycling power support too.
• Apple Watch is the one with published independent validation.
• COROS uses a rolling six-week window.
• Polar offers both a resting test and a per-run estimate.

Sources

• Suunto on Firstbeat features
• Firstbeat on fitness level
• How Suunto calculates your max heart rate

Cover photo by Rollopack, CC BY-SA 4.0, via Wikimedia Commons.