VO₂ max has become a popular metric for categorising overall cardiorespiratory fitness. While elite level endurance athletes often display large VO2 max values, it does not guarantee success as there are many additional factors that are also important. Nonetheless, VO₂ max has become a metric of interest to many recreational athletes and health conscious individuals.
The global wearable technology market was valued at an estimated USD 92.9 billion in 2025 and is expected to reach USD 229.97 billion by 2033. Over the years, more emphasis has been placed on making these devices cover various aspects of fitness and lifestyle with VO₂ max and other fitness metrics becoming central features. The problem is that many of these things are not being measured directly. Instead, proxy data is used to estimate metrics. While these estimates can be relatively consistent, they often lack precision as even the slightest variability in the data collection can have a profound impact on the final calculation. As a result, there are many fitness enthusiasts suddenly believing they are the new record holder for the highest ever VO₂ max.
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What is VO₂ Max?
VO₂ max is the maximal rate at which the body can consume oxygen during exercise. It’s a measure that has often been used to categorise general fitness, as well as general health and mortality risk. It is typically measured in a laboratory setting using breath-by-breath indirect calorimetry. This is collected during a graded exercise test. This test is quite popular in exercise science as it can offer a qualitative indicator of overall cardiorespiratory fitness. This is something that is quite a central interest to many scientific and clinical investigations, as it provides a qualitative appraisal of cardiorespiratory function. This is closely linked with performance, but can also be used to examine the impact of health declines and the impact of certain conditions and diseases.
How Watches Estimate VO₂ Max?
The VO₂ max on the typical fitness watch is an estimate. It is derived from the trends in exercise data, often using GPS pace data and heart rate to guess what your VO₂ max might be. Generally, this requires a bout of exercise exceeding 10 mins in duration that is consistently above 70% of your predicted HR max. The final estimation is often sourced from population-based data, factoring in age, weight, sport and then your run pace and threshold interaction. While these all generally loosely align with measured VO2 data, the absolute value can differ substantially. It is very much an estimate. Directly measured VO2 data requires a great deal of precision to yield a genuine measurement.
Is your watch accurate?
The first thing is that your watch cannot accurately measure VO₂max as it does not measure breath or any breath measurements. So, it cannot make the calculations that indicate your maximal oxygen uptake. What it provides is a best guess based on what someone your age and weight would be at with the level of pace or performance in a given exercise. While this may align with a measured VO₂ max, it is very far removed from an actual laboratory-based measurement.
Why Wearable VO2 Max Can Be Inaccurate?
At the core of wearable technology is the data it utilises. Wearables use a lot of proxy data. In other words, some of the data that are calculated come from something quite different from what they are actually assessing. Often, this is to reduce the number of sensors housed in the device itself. This is the case for Vo2 max where oxygen is not being measured by the watch at any stage. The watch instead uses other training data to estimate, such as running pace and associated heart rate etc. While there is a strong relationship between some training metrics and your Vo2 max, a direct measure is always going to be most accurate. The variance that results in the calculations can become quite large if the original source data is either of poor quality or if the inputs are generally unsuitable i.e. not enough or of the right type. This would be the case if a runner wants to know their Vo2 max from their watch but have not actually saved any run sessions on it.
Does that mean Wearables are Useless?
Often the price and value of a smart watch is based on the features and metrics it offers. If it is incapable of measuring these directly then one would question the value of the metric and its utility. In saying that, the method the device uses is likely to remain consistent; so as long as you provide it with consistent and suitable data it should at least track your fitness trends. It is perhaps ambitious to call the VO₂ max measurement a true VO₂ max but the number it is providing is some form of fitness index that may indicate trends. So, it would be more appropriate to see this value as an indicator of training impact trends rather than a measure of Vo2 max. Higher values would indicate an ability to work harder or longer and vice versa, but not necessarily a high Vo2 max.
The issue with using your watch in this way is it can only assess the information it has on hand. For example, if you have only done easy training over the past months then the watch will calculate based on this training and not off your maximal or harder efforts, which may be absent over this period. It will not have adequate data to predict maximum without some data which can allow it to explore your upper intensity limits.
Where Wearables Are Helpful?
The development of wearable technology places emphasis on repeatability. This means that the metrics provided are relatively consistent. While they lack some precision, they can still indicate trends. This is perhaps where they provide the most benefit: to see progress in fitness or health-related factors, some form of change or progression must take place. While the absolute values being recorded may not be accurate, the direction and magnitude of change can indicate how changes to lifestyle might be translating into longer-term trends. For example, if someone wishes to increase daily activity, daily step count changes would help indicate whether or not they have managed to achieve this or not over time. In addition, reviewing your baseline activity etc, can offer a platform to make more structured planning for new regimes. It is hard to assess progress without knowing the starting point. Wearables allow for rolling data collection over time which can be useful for identifying the longer-term trends. Consistency over time is often what has the biggest impact and so these longer observations can be quite useful.
Why Accurate VO2 Max Testing Matters in Clinical Research
VO₂max is only useful if it is consistent. It is hard to measure accurately in a laboratory setting even if best practice is followed. Using high quality equipment properly is the only way to reduce the many sources of variance and provide consistent and repeatable data. This is critical for investigating the potential impact of a change in lifestyle, training or drug therapy etc. The human performance laboratory at Atlantia Clinical Trials uses a state-of-the-art metabolic cart with both oxygen and carbon dioxide sensors to ensure that measurements are as precise as possible. Calibration is completed with a reference gas to ensure that any discrepancy in measurement is known and accounted for before testing begins. This ensures that the quality of testing is of the highest possible quality. While this is not always possible in field testing facilities, clinical trials require this level of diligence for meaningful observations.
With the cost and complexity of the testing procedures it is important that the test is carried out and assessed by a trained professional. Not all tests should be the same and choosing the right protocol and the interpretation of that data can be difficult. An experienced physiologist may interpret things quite differently to the automatic calculations which many systems provide. This is particularly the case where the individual may have some unusual pattern in their test data which is relatively common to see.
Additional concerns
One additional factor is the reliability of the measurement techniques; many individuals have started to avail VO₂ max testing services. Newer commercial devices allow accessibility to this type of testing through methods which lack some detail. In many cases, they can provide reasonable estimates with less information, making them a cheaper option. More accurate clinical level devices are very expensive due to the level of precision required. Reducing key processes and calculations and allowing for estimates can have substantial implications for the meaningfulness of the insights they provide. Due to the appearance of the equipment being highly specced it misguides people into thinking they are getting something more genuine and accurate which is not always the case. Test conditions must also be well controlled and appropriate. For example, the modality of exercise will have an impact on VO₂max yet many are not informed of this. Fatigue and even familiarity with the test can also impact results.
Conclusion
The commercial fitness market is a mine field for genuine and or useless technology. Clever marketing has blurred the lines between science and advertising. While activity watches can be of great use and quality, some of their metrics are often misrepresented. Proxy data can only be used for estimations. In many cases, we are trying to interpret quite precise data with imprecise information, so the quality of the interpretation must be questioned. In the case of the watch calculated VO₂ max, one must realise it is not a true reflection of your VO₂ max but it may be some reflection of your general fitness status. Realising can prevent some disappointment but also allow for it to be used in a more effective and beneficial way.
Frequently Asked Questions
Is the VO₂ max on my smartwatch accurate?
Rarely, although many judge the variance as acceptable. Without substantial calibration and direct measures of respiration any VO₂max estimate is very much just an estimate.
Why is my VO₂ max different from a lab test result?
Because the equipment in a lab offers a much greater ability to measure accurately as a complex system of sensors measures gas exchange directly.
How is VO₂ max measured in a laboratory?
The VO2 max is measured in a laboratory using breath-by-breath gas exchange analysis paired with an appropriate exercise testing protocol.
What is the gold standard method for measuring VO₂ max?
Usually, a graded exercise test with cardiorespiratory analysis is the gold standard method for determining VO2 max.
How do watches estimate VO₂ max?
Most commonly, they estimate using an algorithm that factors age, weight, exercise intensity and heart rate response.
Should I trust my watch’s VO₂ max score?
It will reflect recent fitness trends but it will not be a true 100% reflection of your VO₂max.