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We may earn a commission from links on this page.Whoop, the screenless watchband-like wearable that beat out Oura in my non-watch fitness tracker showdown, has just added a VO2 max feature to its app. Now, just like Garmin, Apple Watch, and others, it can put a number on your cardio fitness and tell you how it changes over time. WHOOP 4.0 with 12 Month Subscription Wearable Health, Fitness & Activity Tracker $239.00 at Amazon Get Deal Get Deal $239.00 at Amazon What is VO2 max again?VO2 max is a measure of cardiovascular (or aerobic) fitness. There are other types of measurements that can give you a sense of how fit you are, but VO2 max is one of the simpler metrics to follow. Its a two-digit number, and the higher it is, the fitter you are. A sedentary person might have a VO2 max around 20; an athlete might have one over 50.The technical definition is that its the maximum amount of oxygen your body can use per minute while exercising, divided by your body weight. The higher that number, the better your heart and lungs are at getting oxygen to your muscles, and the better your muscles are at using energy for exercise.How is VO2 max measured?To get a true VO2 max reading, you need to take a test in an exercise lab with a max that measures the amount of oxygen youre breathing. Obviously, a wearable cant provide that on its own. But wearables like Whoop, Garmin watches, and Apple Watches can estimate your cardio fitness through other means.Most commonly, theyll compare your heart rate to how quickly you can run or walk. If you can jog along at a pretty fast clip while your heart rate is low, youre probably pretty fit and have a high VO2 max. On the other hand, if your heart rate soars when youre just trying to go out for an easy walk, you probably have low cardio fitness and thus a low VO2 max. Thats the general idea, anywaythe exact calculation will vary from one device to another.How Whoop uses VO2 maxI expected Whoop to use the same walking/running-based type of calculation as the other wearables Im familiar with, but the companys description makes it sound like something more complicated (and harder to verify) is going on.Whoop estimates your VO2 Max using a proprietary algorithm trained on gold-standard laboratory data from a diverse set of Whoop members, it says. Thats not very helpful. It continues: To calculate your score, the algorithm factors your continuous physiological data (including resting heart rate and heart rate variability), your exercise patterns, and GPS-tracked performance metrics (when enabled). It also accounts for how VO2 Max naturally changes with age and incorporates physical factors that influence oxygen utilization, like height, weight, and biological sex.So GPS-tracked activities can be included in the calculation, but apparently arent necessary. This makes me wonder what the Whoop band is actually measuring to determine your VO2 maxor is it just doing some kind of AI-powered guess at what people with your metrics tend to have as their VO2 max? Ive reached out to the company and will update if it is able to give me more information.I dont have a VO2 max in my Whoop app at the moment, since it requires 14 recoveries (nights of sleep, basically) to give you that information, and I havent been wearing my Whoop lately.Where to find your VO2 max in the Whoop appAccording to Whoop support, you can find this feature on the Strain tab. By tapping VO2 max you can view monthly or six-month trends. Users on Reddit have reported that its been rolling out over the past few days, and that Whoop has told them everybody should have it by March 13 (today).