To move, think, digest food, and otherwise do anything, your body needs oxygen. This important fact is what makes VO2 max such a useful measure of fitness. It’s also extremely useful that some fitness trackers can now offer a VO2 estimate.
Your VO2 max is the amount of oxygen you’re able to utilize during training. A higher score correlates with greater aerobic fitness, more energy, faster recovery, and better overall health.
We’re taking an in-depth look at how VO2 max is measured, how accurate fitness trackers are in measuring it, and what you should do about your numbers.
VO2 max explained
VO2 max is also referred to as maximal oxygen consumption, maximal oxygen update, or maximal aerobic capacity. The figure represents the amount of oxygen you’re able to consume in one minute per kilogram of body weight (mL/kg/min).
This, in turn, means greater delivery of oxygen to the muscles during exercise. This is dependent on several different factors: the amount of oxygen you draw in on each breath, the arteriovenous oxygen difference (the quantity of oxygen taken up from the blood by tissues), the number of red blood cells, your maximal cardiac output (Qmax), and more.
VO2 max serves as a predictor of aerobic performance: long-distance running and other activities. These activities rely on the aerobic energy system (instead of the phosphagen lactic-acid or ATP-creatine systems). In plain English, you have depleted all the readily available energy stores in the muscles and bloodstream and must begin burning fat stores for more fuel. You can continue to do this indefinitely, as long as you maintain a steady pace. This is what we mean by the “fat-burning zone.”
The better your VO2 max, the faster you will be able to go without burning out.
However, if you attempt to run faster and your heart rate exceeds a certain point, you will be forced to switch back to an energy system that relies on available energy stores. This is when we start to feel the gradual build-up of hydrogen in our muscles that forces us to slow down again. (In truth, we actually use all three energy systems, at all times, to varying degrees.)
This way, VO2 max is directly linked to the anaerobic threshold: the point at which we must switch to anaerobic (less efficient) energy systems. The better your VO2 max, the faster you will be able to go without burning out.
VO2 max is linked with the density of mitochondria. Mitochondria are the energy factories of the cells, responsible for roughly 95% of your energy needs. These are the worker bees responsible for turning the fat, glucose, and amino acids into usable energy in the form of ATP.
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Training can cause changes in both the number and efficiency of mitochondria on a per-muscle basis. If you do a lot of long-distance running, you will see an increase in mitochondria, specifically in the leg. Rowers might find they have a proportionately larger quantity of mitochondria in the lats/arms. Thus, a rower might get a higher VO2 score when rowing versus running.
Seeing as we also utilize the aerobic system during everyday activities, it should come as no surprise that a better VO2 max also correlates with better general health. For example, a higher VO2 max predicts improved brain function. While a correlation does not establish causality (the act of exercising also improves cognitive function), it’s fair to assume that greater oxygen delivery to the brain could improve performance.
How is VO2 max measured in a lab?
As you are probably already sensing, this is a rather complex figure to calculate as it is dependent on many factors. The only way to get a truly accurate reading of your VO2 max, therefore, is to visit a lab and subject yourself to an expensive battery of tests.
During this test, the athlete will be asked to run on a treadmill or cycle ergometer. They will then be gradually pushed to the point of total exhaustion. During this time, a technician will take several measurements such as ventilation and oxygen/carbon concentration of the inhaled/exhaled air. In other words, they measure precisely the amount of air being taken in and how much oxygen is removed from that air.
Once the amount of oxygen consumption peaks at a steady rate, the VO2 max has been reached. It is a grueling test!
Fitness trackers and other tools for measuring VO2 max
So, how is it that fitness trackers also claim to offer an estimated VO2 max?
The key thing to recognize about the VO2 max score generated by your Fitbit or Garmin device is that this is very much an estimate. However, there are methods to generate a rough score using simple equations and tests that can be carried out at home. Fitness trackers rely on similar methods.
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One such method, called the heart rate ratio method, uses maximum and resting heart rate measures. This method uses a ratio of maximum heart rate to resting heart rate. That figure is then multiplied based on factors such as age, illness, gender, etc.
Another test is the Cooper test. This method requires the athlete to run as far as possible within 12 minutes. The VO2 max is then generated based on the distance covered. Such methods’ limitations should be immediately obvious; even something as simple as leg strength or stride length can significantly impact the results.
The “beep test” (aka multi-stage test) is also used to provide an estimated VO2 max. As you may remember from your old PE class, this involves running 20 meters back and forth while keeping time with the beeps.
Finally, the Rockport fitness walking test uses data from a one-mile track walk. The heart rate at the end of the walk is used in conjunction with bodyweight, age, gender, and more.
Fitness trackers rely on similar methods to calculate a rough VO2 max. Most devices that show this data will only do so after you have worn the device for several runs and walks, at which point they will be able to offer a somewhat accurate score.
As we have seen, these methods are imperfect. There is no way that a fitness tracker can have all the information necessary to accurately measure oxygen consumption. Nor do most trackers consider all relevant individual data such as a history of smoking, health conditions, etc.
What fitness trackers do have going for them, however, is the sheer amount of data. Seeing as fitness trackers can monitor your heart rate during training and rest and even measure things such as stride length, they have plenty of data to generate a useful figure. Using GPS data and altitude measurements, they could even estimate oxygen levels in the environment.
Most companies are not particularly transparent about the precise algorithms they use to generate their scores.
Unfortunately, most companies are not particularly transparent about the precise algorithms they use to generate their scores. This may be partly due to fear of competitors using the same strategies. More likely, it is to avoid critique that may call into question the validity of their scores. This is also why companies like Fitbit cleverly use alternative names for these metrics. In this case, Fitbit refers to a “cardio fitness score.”
Either way, these numbers are still useful for guiding your training. What is more important than accuracy is consistency. As long as the testing method remains the same, you can monitor your progress.
Just keep in mind that professional athletes should not rely on such methods to guide their zone training or similar. In all likelihood, if you fall into that camp, you’ve probably already been subjected to the real deal by your coach.
What is a “good” VO2 max score?
Elite athletes can exhibit VO2 max scores as high as 80mL/kg/min. Conversely, animals such as Alaskan huskies may even achieve a VO2 score over 200mL/kg-min!
For the rest of us, anything between 30-60 is generally considered a normal range. The following table gives you an idea of how you measure up:
How can you raise your VO2 max?
Some strategies may improve VO2 max. Generally, any form of endurance training will have some benefit in this regard.
HIIT is particularly effective. This makes sense when you consider that the protocol repeatedly involves “maxing out” your aerobic system. That said, low-intensity steady-state exercise, such as jogging, can also offer unique advantages. For example, this can improve your Qmax or quantified maximal cardiac output, which correlates with heart size and strength.
Threshold training involves running as fast as possible without causing a build-up of hydrogen in the muscles (and a corresponding increase in lactate, though this is not what causes muscle fatigue).
In other words, the best way to improve VO2 max is to train at different speeds and to thus work every energy system.