Plenty of fitness trackers these days will tell you your VO2max, sometimes referring to it as a “cardio fitness” score or telling you that you’re fitter than a certain percentage of the population. While it’s fun to watch this number change as you train, it’s not necessarily a good measure of your fitness.
Fitness can be tested and measured in many ways, and no one metric can possibly give a complete picture. For example, someone might be strong enough to deadlift 363 kg, but be unable to do more than a handful of push-ups. Somebody else might be a fast sprinter, but end up at the back of the pack in a long-distance run. Our muscles, lungs, and all our other body parts work together to produce athletic performances, and there’s no single number that can define “fitness.”
What is VO2max anyway?
We have a whole explainer here, but briefly: the higher your VO2max, the harder your body can work for extended periods of time. A person with a higher VO2max can outrun a person with a lower VO2max, all things being equal, because they can sustain a higher speed during their workout.
It’s called VO2max because the traditional way of testing it — in a lab, where you’re hooked up to a breathing mask — is to measure the greatest (max) volume (V) of oxygen (O2) you can take in and make use of per minute. (It’s measured in milliliters of oxygen used in one minute per kilogram of body weight.)
Higher is better; a person who doesn’t do much cardio may have a VO2max in the 20s, while an endurance athlete may have one in the 40s or higher. Age and gender also affect your numbers, with women typically having a lower score than men, and older people scoring lower than younger people. (That’s why fitness trackers will often compare your score to others of your age and gender.)
Is it accurate?
Fitness trackers estimate your VO2max from the data they are able to collect. So, no, they aren’t as accurate as getting a VO2max test in a lab. The number may still be useful, though.
Typically a tracker uses your heart rate and your speed during a distance workout (such as running) to make an educated guess at how good your cardio fitness is. If your heart is beating out of your chest when you run a 10-minute mile, you probably have a lower VO2max than a person whose heart rate only increases a little bit over resting when they run a 10-minute mile.
The actual calculation uses other factors, including your weight, since VO2max scales relative to your body weight — so if you want to keep an eye on your VO2max scores, make sure your information in the app is up to date. And make sure you actually go for a run every now and then to feed it data. If you never do the kind of workouts that your gadget uses to gauge VO2max, you won’t get an accurate or useful reading.
To find out what workouts those are, look up the specifics for your watch. Typically they look for running or fast walking workouts that last for at least 10 minutes, and that get your heart rate up into a reasonable cardio zone. You’ll also get the most accurate results if you are on flat ground and not chugging up hills. Here is Fitbit’s explanation and Apple’s explanation of how they calculate VO2max. Garmin, never to be outdone, has five different ways it can calculate VO2max.
What can I learn from my VO2max score?
Assuming you’re getting the most accurate estimate your gadget can provide, all there is to do is watch your VO2max increase as you improve your cardio fitness. If you follow the numbers religiously, you might panic slightly if you take time off and see it change — which I would say is a good argument not to pay too much attention to it.
After all, why are you exercising? If you’re training for a race, your training and time trial paces should let you know whether you’re getting faster. If you’re doing cardio just for your general health, sticking to a reasonable schedule automatically means you’re getting the work done no matter what happens with your numbers. So consider whether this number is useful to you or not.
All that said, if you want a better VO2max, you can do cardio exercise more often, more consistently, and occasionally at faster paces. Long slow workouts and short fast workouts both work to increase your cardio fitness, and an ideal exercise program will include both.
I work out every day. I don’t really get sore. I don’t worry if I have to miss a workout. I make progress over time. I have good days at the (home) gym, but I almost never have bad days. My secret, while effective, is extremely boring. It is, simply,...Read more
What doesn’t VO2max tell me?
Your estimated VO2max doesn’t tell you how strong your muscles are. It doesn’t tell you how agile you are or how skilled 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 needed to run long races. It can’t even tell you what your actual VO2max would be if you got a lab test.
The sports world is full of people who were told that some metric — sometimes their VO2max, sometimes another number — would limit them, and then they went on to succeed anyway. It’s also full of people who have good numbers, but never managed to live up to them. Runner’s World points out that an 18-year-old cyclist who clocked the highest known VO2max ended up retiring from his sport a few years later after a “short, underwhelming pro career.” Bottom line: VO2max isn’t everything.