There's been an increasing focus on VO2 Max from the latest fitness wearables, with Garmin, Fitbit and Jabra all choosing to make use of a metric that was once only for elite athletes with access to sports labs.
We wrote a big explainer piece on VO2 Max and the science behind both the metric and how it's measured, so if you want to know more, we'd suggest heading there first. (Essentially, it's the maximum volume of oxygen which is transferred to the blood. The fitter you are, the higher the amount of O2.) Explaining the tech got us interested – how accurate is current VO2 Max tracking compared to a lab test?
In stepped Nuffield Health. The health and fitness company is a giant in the UK and it's built a brand-new specialist sports performance lab at its City Fitness and Wellbeing gym in London. Nuffield kindly let us try a full VO2 Max test.
Under the watchful eye of Vince Christian, clinic manager & senior physiologist, we were strapped up for the test. If we're out to compare wearables vs VO2 Max tests, consumer tech already has a one-up. The VO2 Max test is pretty horrible, involving getting on a treadmill with a face mask on to capture every molecule of oxygen inhaled and exhaled. Not only that, but after every phase of the test, your finger is pricked to take a sample of the oxygen in your blood.
The test itself is pretty gruelling too. A couple of brisk walks are followed by two rapid uphill climbs, the second of which has me on my knees. VO2 Max had been reached.
The lab test put my VO2 Max at 47.9 ml/kg/min – which just puts me into the "excellent" fitness category for a man of my age, weight and height. While a downside of the test was that I tapped out before a long plateau of VO2 was shown on the graph, the fact that I couldn't physically continue was indication that the figure was accurate.
So how do consumer wearables compare? We hit the roads to find out.
Fitbit Charge 2
The Fitbit Charge 2 is the newest and most advanced tracker from the company to date, and makes use of VO2 Max as an indicator of overall fitness, renamed Cardio Fitness.
To get a Cardio Fitness score, Fitbit asks you to go on a run with Connected GPS enabled for at least 10 minutes. It also takes into account your resting heart rate and body details.
We've tested the Cardio Fitness element of the Fitbit Charge 2 a number of times, but the final run was at the same time as we carried out the Jabra Sport Pulse's VO2 max test below.
So what were the results? During the review process for the Fitbit Charge 2 we noted that VO2 Max was a little high, and this is something that was borne out by our comparison test. VO2 Max was scored at 53 ml/kg/min, way above the lab test. What we will say is that in our review testing period recently, we were scored at 49, so we're not sure what's caused the big jump in VO2 Max this time around.
To put the result in context, a score of 53 ml/kg/min in the Fitbit app is ranked as "very good". A score of 47.9 ml/kg/min, as per the lab test, would only be ranked as "good". So in terms of numbers the test is quite far out, but at least the feedback is consistent.
Read our full Fitbit Charge 2 review.
Garmin Fenix 3 with chest strap
We paired the Garmin Fenix 3 with a chest strap to see whether this was the key to a better VO2 Max test. Again, the parameters for an accurate test are pretty loose, and it just asked us to run for 10 minutes outdoors with the heart rate monitor attached.
Using a chest strap doesn't offer the resting heart rate data enjoyed by the Fitbit Charge 2, so it's only based on running. And perhaps unsurprisingly, the Garmin was the most accurate, clocking our VO2 Max at 48, pretty much spot on in terms of accuracy.
In terms of interpreting that accuracy, the Garmin has me on the very upper edge of a "good" fitness rating, just 0.3 ml/kg/min short of "excellent".
Read our full Garmin Fenix 3 review
Jabra Sport Pulse SE
We tested the VO2 Max on the Jabra Sport Pulse a few times during our review period, and always found it to be a little low. But how did it fare against the Nuffield Health sports lab?
VO2 Max is taken after any run when using the Jabra Sport Pulse and the Jabra app, but given that there's a dedicated VO2 Max test included, we opted for that. The test involves running for 15 minutes and you need to keep your heart rate between 70% and 100% of max heart rate, which makes it the most stringent of the devices on test.
And the VO2 Max confirmed our suspicions. An outcome of 46 ml/kg/min was a little below the lab score. That's been consistent across our testing, and I got a reading of 47 ml/kg/min back in the summer, when I was arguably far fitter, at the back end of my heart rate training diary.
In terms of feedback the Jabra Sport Pulse SE had me firmly in the "good" camp, a long way from the "excellent" feedback from most other devices on test.
Read our full Jabra Sport Pulse Special Edition review.
This is the start of an ongoing process, but what's clear is that when it comes to VO2 Max, Garmin's superior algorithms (and the presence of a chest strap) won the day. Whether Garmin could maintain that accuracy using the optical heart rate tech on the Forerunner 235 or 735XT remains to be seen. There's much more scope for further testing.
Arguably it's all about the feedback, and your ability to affect the scores. And even in the case of Fitbit, the feedback echoed that of the sports lab. Our testing has found the score to be responsive enough to regular training.
But it shows that while a rush to embrace laboratory grade metrics is good for fitness fans, there's still a lot of work to be done to deliver professional level results. We're locked into a constant argument of what's "good enough" here at Wareable – and that's very much up to the user.