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Today, many fitness trackers give you your VO2max, sometimes referred to as “cardio fitness” or advising you that you are fitter than a certain percentage of the population. While it’s fun to see this number change as you workout, it’s not necessarily a good measure of your fitness.

Fitness can be tested and measured in many ways, and no metric can possibly provide a complete picture. For example, someone might be strong enough to lift 800 pounds but not be able to do more than a handful of pushups. Someone else might be a fast sprinter, but end up at the very back of the pack over a long distance. Our muscles, lungs, and all other parts of the body work together to produce athletic performance, and there is no single number that can define “fitness”.

Illustration for article titled What Your VO2 Max Score Really Means

What is VO2max?

With the news that the Apple Watch will soon be able to measure VO2max more effectively (it says) …

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What is VO2max anyway?

We have a full explainer hereBut in short, the higher your VO2max, the harder your body can work for longer periods of time. A person with a higher VO2max can overtake a person with a lower VO2max, all things being the same as they can maintain a higher speed during their exercise.

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It’s called VO2max because the traditional method of testing – in a lab where you’re attached to a breathing mask – is to measure the largest (maximum) volume (V) of oxygen (O2) you can take in and use of per minute. (It is measured in milliliters of oxygen that is consumed in one minute per kilogram of body weight.)

Higher is better; A person who doesn’t do a lot of cardio may have a VO2 max in their 20s while an endurance athlete has one in their 40s or higher. Age and gender also affect your numbers, with women typically having a lower score than men and older people scoring fewer points than younger ones. (This is why fitness trackers often compare your scores to those of your age and gender.)

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Is it accurate?

Fitness trackers estimate your VO2 max based on the data they can collect. No, they are not as accurate as a laboratory VO2max test. However, the number can still be useful.

Typically, a tracker uses your heart rate and speed during a distance exercise (such as running) to make an educated guess about how good your cardio fitness is. If your heart is beating out of your chest while running a 10-minute mile, you likely have a lower VO2max than someone whose heart rate increases only slightly while running a 10-minute mile.

The actual calculation uses other factors, including your weight, as VO2max scales relative to your body weight. So if you want to keep an eye on your VO2max values, make sure your information in the app is up to date. And make sure you actually take a run every now and then to enter the data. If you never do the kind of exercise your gadget uses to measure VO2max, you will not get accurate or useful readings.

To find out what workouts it is, read the details for your watch. Typically, they look for running or fast-walking workouts that last at least 10 minutes and get your heart rate within a reasonable cardio zone. You will also get the most accurate results when you are on level ground and not chugging uphill. Here is Fitbit’s explanation and Apple’s explanation how they calculate VO2max. Garmin never managed to be outdone VO2max can be calculated in five different ways.

What can I learn from my VO2max score?

Assuming you get the most accurate estimate your device can give, all you have to do is watch your VO2 max increase as you improve your cardio fitness. If you followed the numbers religiously, it could be easy to panic if you take some time off and see this change – what I would say is a good argument not to pay too much attention to it.

Why are you training? When you’re training for a race, your training and time trial steps should help you know if you’re going to get any faster. If you’re only doing cardio for your general health, sticking to a sensible schedule automatically means you’ll get the job done regardless of what happens to your numbers. So, think about whether or not this number is useful for you.

However, if you want better VO2 max, you can do cardio exercise more often, more consistently, and occasionally faster. Long slow workouts and short quick workouts will improve your cardio fitness, and an ideal exercise program will include both.

Illustration for article titled What Your VO2 Max Score Really Means

What does VO2max not tell me?

Your estimated VO2 max doesn’t tell you how strong your muscles are. It doesn’t tell you how agile you are or how good you are at your sport. It doesn’t tell you how efficient your stride is, or whether you are good at the mindset or planning required for long races. It can’t even tell you what your actual VO2 max would be if you were given a lab test.

The sports world is full of people who were told that one metric – sometimes their VO2 max, sometimes a different number – would limit them, and then they succeeded anyway. It’s also full of people who have good numbers but never managed to live up to them. Runner’s World points this out that an 18-year-old cyclist who rode the highest known VO2max, retired from his sport a few years later after a “short, not exactly convincing professional career”. Conclusion: VO2max is not everything.