Many users of the Apple Watch have used it to track steps and stay active. VO2 max, a measurement of how much oxygen the body consumes during intense workouts, is also a watch tracked statistic. If you increased activity is making you more fit, the Vo2 max should show this.
But measuring the amount of oxygen you consume has to do with the lungs and heart, not your wrist. So how accurate is the reading on the Apple Watch?
If you have monitored workouts for a while you may see weird spikes in the estimated reading. That is likely because the wrist worn, blood oxygen concentration monitoring watch uses a calculation to get a VO2 max result. If the equation used to calculate changes, as it does during software updates in order to improve accuracy as the technology and science develop, you may see a spike.
Without a software update, the accuracy of the watch is still pretty good. It’s unlikely to fluctuate day to day so trends over time are easy to spot.
The image above show the trends of VO2 Max from a watch during a training cycle. Starting at 15-20 miles of running per week and moving up to 45-50 mile weeks over the course of a few months the trends are obvious.
Even with the jumps from software updates, it’s easy to see that the reading at least tracks general fitness. So is a more accurate reading necessary? If all you are looking for is a metric to encourage continued training and wellness improvement, the trend from a wrist worn calculation should be just fine.
DexaFit VO2 Max Accuracy
The term “accuracy” assumes you know the true measurement. DexaFit, like other wellness centers, uses a mask based monitoring system to read your true VO2 during a 10-20 minute hrs effort.
The duration of the test is based on performance, you can opt out on your own. During an initial test this might be at a sub Mac effort. Personally, running at full 15% incline on a treadmill, while breathing into a mask that at least partially resists breathing in (or mentally makes you think that), was not normal. I pulled up on the test probably 20-30 seconds prior to complete exhaustion, but still was happy with the test. The examiner agreed most people can perform better on a second test just from the mental aspect. Other situational cues, a coach cheering you ow , a competitor on the treadmill next to you, good music, etc. all could have impact on the mental ability to push the test.
Regardless of the settings, the accuracy of the measurement of this test style is closer to actual. If you manage to get to exhaustion, the peak is likely to be your max. Having done the test, where my heart rate peaked (178bpm) about 7-8 beats below what I’ve observed during workouts (185bpm), it appears the treadmill DexaFit measurement aligns well with an Apple Watch prediction.
In total the treadmill was 53.9 mL/kg/min which is ~7% lower than the Apple Watch 57.9mL/kg/min predicted just a day before during a run.
With the treadmill test being so similar to the Watch predictions on VO2 max accuracy,, what good is a treadmill test.
A secondary, and arguably primary, benefit to the treadmill test is to see when you pass through threshold levels. For heart rate training this is key. Below a factor of 1, your body is clearing lactic acid at a rate faster than its building up. This is the threshold at which burning starts accumulating in muscles. In endurance athletics keeping this heart rate in mind is the difference between hitting the wall and finishing strong.
Because the treadmill test starts at a warmup and escalates to max effort, you can monitor these zones. This again is something that can be estimated by calculators, and you can set your watch to alert you at different zones, but this is a personalized measure and knowing your own body can help make the small differences that the calculators will not enable.
Overall both the treadmill test and the watch estimate provide the same results. The VO2 max accuracy is close enough on either to get to the right general zones to monitor fitness. With the cost of a clinic treadmill test being higher ($49-$149 depending on location) it is more costly to find trends.
A watch does a good enough job to showcase if fitness is improving overall. The clinic treadmill tests are a solid option for an occasionally check-in, and can be used in a similar way that a time trial or a target race is as a way to motivate you during a training cycle.