Beyond the Watch: What a VO₂ Max Test Really Tells You

As a triathlete and coach, I spend a lot of time talking about training zones, pacing, heart rate and performance data. Like many athletes, I also wear a sports watch and use it to monitor my training and recovery.

But how accurate are the numbers we see on our wrists? And how much more can we learn by testing our physiology directly?

I recently visited Damini at The House of Misogi in Harrow for a resting metabolic rate (RMR) assessment and a VO₂ max test on the bike.

I was interested in seeing what the results would tell me about my current fitness, and whether they would confirm what I already thought I knew about my training.

It turned out to be a really interesting experience.

First up: Understanding my resting metabolism

The session began with an RMR test. This measures how much energy your body uses at rest to maintain essential functions, such as breathing, circulation and keeping your organs working.

The process was straightforward. After a short calibration period, I wore a breathing mask and lay down for 15 minutes while the equipment measured my oxygen consumption.

There was nothing particularly strenuous about it. In fact, once I had settled into the mask, it was simply a case of lying still and relaxing.

The results suggested that my resting metabolic rate was around 26% higher than the prediction used for comparison. This was an interesting finding, reflecting the amount of training I do and the muscle mass I have developed through years of swimming, cycling, running and strength work.

It was also a useful reminder that generic calculations are just estimates. Individual physiology varies, and measuring it directly can provide a more personalised starting point.

Of course, RMR is only one part of the picture. It tells us how much energy the body uses at rest, not exactly how much we burn during training or across an entire day.

The assessment also provided an estimate of my total daily energy expenditure based on my reported activity levels. That figure is useful as a guide, but it is still an estimate rather than a precise measurement of everything I expend.

For me, the main value was having a baseline rather than another number to obsess over.

The main event: My VO₂ max test

Next came the VO₂ max test.

VO₂ max is a measure of the maximum rate at which your body can take in, transport and use oxygen during intense exercise. It is commonly used as an indicator of aerobic fitness, although endurance performance depends on much more than VO₂ max alone.

The test involved cycling on a stationary bike while wearing the breathing mask and a heart-rate monitor.

We started with a five-minute warm-up before the resistance increased progressively, minute by minute. The aim was to continue for long enough to collect meaningful data and reach a genuinely demanding level of effort.

My reported VO₂ max was 57.7 ml/kg/min.

That was a pleasing result, although the number itself was only part of what interested me (although it was strikingly different to the test I did 6 years ago on a treadmill when it was just 47.8). I wanted to understand what the test could tell me about my training intensity, thresholds and potential training zones.

The assessment also recorded my heart rate, power output and breathing responses as the workload increased.

One of the most interesting parts was discussing how the data should be interpreted. The equipment produces a lot of information, but the results still need to be reviewed by someone who understands the testing protocol, the graphs and the individual being tested.

A graph can suggest where physiological thresholds occur, but those estimates need to be checked rather than accepted automatically. The quality of the interpretation matters just as much as collecting the data.

Why my watch doesn't tell the whole story

My watch had previously estimated my VO₂ max at around 49, compared with the laboratory-style assessment result of 57.7.

That is a substantial difference.

It doesn't necessarily mean that every watch is inaccurate by the same amount, or that a direct test is completely free from measurement error. The methods are different, and results can vary with the equipment, protocol, conditions and how the data is analysed.

However, it does demonstrate why we should be careful about treating a wearable estimate as an absolute measure of fitness.

Watches are brilliant tools for tracking trends, monitoring heart rate and helping us stay consistent with training. But their estimates are not the same as directly measuring oxygen consumption during a graded exercise test.

As a coach, I see this regularly. Athletes can become fixated on the numbers displayed on their devices, sometimes questioning their fitness or hanging their training because an estimate has moved in the wrong direction.

The reality is that one number rarely tells the whole story.

Finding the right training zones

For me, the practical value of the test was understanding how the results could inform my training.

The assessment estimated two important physiological thresholds: the first ventilatory threshold (VT1) and the second ventilatory threshold (VT2).

In simple terms, these help us understand how the body's breathing response changes as exercise intensity increases.

VT1 is particularly useful when considering sustainable aerobic training. VT2 helps identify a higher-intensity boundary associated with a substantially greater physiological demand.

These thresholds can help inform training zones, but they should not be confused with a complete training plan.

For triathletes, the aim isn't simply to accumulate as much time as possible at a particular heart rate. We need to consider the purpose of each session, the demands of the sport, training history, recovery and how the athlete responds over time.

My test also suggested that my previous cycling threshold setting might need reviewing. We discussed the possibility that my functional threshold power (FTP) could be closer to 180 watts than my existing setting of 165 watts.

However, a VO₂ max test does not directly establish FTP. A separate threshold assessment or appropriate training data would be needed to confirm that figure.

That distinction is important. The results can help us make better-informed decisions, but they should not be used to assign training numbers without considering what each measurement actually represents.

For me, the next step is to review the detailed report, consider the proposed training zones and see how they align with my experience during training.

You don't have to be an elite athlete to benefit

One of the things I particularly liked about the experience was the conversation about making this kind of testing accessible to people who aren't competitive athletes.

Physiological testing is often associated with elite sport, university laboratories and expensive private performance clinics. But understanding your own physiology can be useful for a much wider range of people.

For someone returning to exercise, it may help establish a baseline from which to monitor progress. For a recreational runner or cyclist, it could help inform training intensity. For someone interested in improving their general fitness, it may offer another way of understanding their current aerobic capacity.

The key is using the results appropriately.

A VO₂ max test is a maximal or near-maximal exercise assessment, depending on the protocol, so it isn't automatically suitable for everyone. Health screening and appropriate supervision are important, particularly for anyone with relevant medical conditions or concerns.

Nor does everyone need a VO₂ max test to improve their health. Consistent physical activity, sensible progression, good recovery and appropriate nutrition remain fundamental.

Testing is a tool, not a requirement.

What about the limitations?

As interesting as the results were, there are a few things worth remembering.

First, the numbers are not the whole picture. VO₂ max is one measure of aerobic capacity, but endurance performance also depends on factors such as movement economy, sustainable threshold intensity, pacing, technique and the ability to tolerate training.

Second, results depend on the testing process. Equipment, calibration, protocol selection and interpretation can all influence the information we obtain. Comparisons between tests are most meaningful when the conditions and methods are sufficiently consistent - as noted above with the different test I completed 6 years ago.

Third, one assessment is only a snapshot. Sleep, fatigue, recent training, nutrition and other factors can influence how we feel and perform on a given day. If the goal is to monitor change, repeating the assessment under comparable conditions is more useful than drawing conclusions from a single result.

And finally, testing only becomes valuable when we do something useful with the information.

A report full of graphs and numbers might look impressive, but the real question is what it means for the individual sitting in front of you.

My takeaways as a triathlete and coach

I went into the session curious about what the data would show. I came away with a better understanding of my current physiological profile and some useful questions to explore in my training and how this could be used with my athletes.

The biggest takeaway was not simply that my measured VO₂ max was higher than my watch estimate. It was the opportunity to look beyond the headline number and consider how the information could be used to make more informed training decisions.

For athletes, this can help refine training zones and provide a baseline for future comparison. For coaches, it can add another layer of information to support conversations about training intensity, performance goals and progression.

But data should support coaching, not replace it.

The numbers need to be interpreted in context, discussed with the athlete and considered alongside what happens in training and competition.

And perhaps most importantly, we shouldn't allow a watch, a test or a graph to dictate how we feel about our fitness.

Sometimes the data confirms what we already suspected. Sometimes it challenges our assumptions. Either way, it is most useful when it helps us understand ourselves a little better.

For me, that is what good sports science should do: turn measurements into meaningful information, and meaningful information into better decisions.

Finally, now you have got to the bottom of the story, Damini is happy to offer a further discounted price for the combined assessment as long as you write my name down while booking under 'referred by' - this would be at £105.00