As a Slow Down and Saver, prioritising health is just as important as managing money. Whether you’ve taken up running, CrossFit or regular gym sessions, staying active is essential for a long, independent life.
But with so many metrics – heart rate, triglycerides, fat oxidation – it’s easy to feel lost. That’s why I focus on a single, powerful measure: VO2 max, the ultimate metric for health, fitness and longevity.
This metric captures the efficiency of your heart, lungs, blood, and muscles all working together, predicting both fitness and longevity more accurately than anything else. In this post, I’ll explain why VO2 max matters, how to track it easily with a smartwatch, and how improving it can transform your health well into old age.
Don’t get lost in the minefield
The world of health and fitness is excessively large and complicated – it often seems only to confuse and discourage (much like with investing). (Strangely similar to personal finance and investing.) As you investigate further and begin to research the science behind longevity, you’ll stray into a minefield of health terms such as triglycerides, Apo B, lactate testing, fat oxidation… I soon found myself thinking “this is great, but I’m not trained in medicine, nor am I particularly interested in these health terms“.
Yes, these variables can all be tested independently to give you the clearest possible picture of your health (you can spend over £1,100 on a comprehensive health assessment these days), but I’m just not that interested. I was yearning for a few simple metrics that I could track, ideally with a smart watch, to monitor my overall health. Fortunately, there is one single metric we can use to measure overall health and fitness better than anything else;
VO2 max
You may have already heard me banging on about VO2 max. It’s my favourite metric to keep track of my health; I keep track of it daily.
VO2 max is a measure of the maximum rate of oxygen your body can consume and utilise during intense exercise. It is the gold standard for measuring cardiovascular fitness. It is the single strongest predictor of longevity we know of. Nothing beats it. It effectively measures how efficient your body is at being alive. It reflects a harmony between the lungs, heart, blood vessels and muscles, and represents the entire oxygen chain within your body.
A higher VO2 max means better overall fitness, allowing you to work harder for longer, and it’s strongly linked with better health and longevity. It’s measured by pushing your muscles to physical failure in a lab test, usually by wearing a respiratory mask to measure oxygen flow while running on a treadmill up progressively higher inclines.
How to measure VO2 max with a smartwatch
Most smartwatches provide a proxy of VO2 max by measuring heart rate and GPS signals. The precise methodology will vary from device to device, but typically uses a complex algorithm combined with deep neural network machine learning to give an estimate.
For example, when developing their VO2 max calculations in 2021, Apple wrote a paper on how accurately their smartwatches measured it vs lab test results. They found a median standard deviation of 3.4% (221 users total), and a 90th percentile of 7.2%. That’s pretty good for the general population, unless of course you want to shell out £95 as well as your time to travel to a lab and get a physical test.
Garmin smart watches look to be a little less accurate; perhaps within 5% of the true value for frequent outdoor runners, and 10-15% for recreational users.
Get a used smartwatch!
I use an Apple Watch Series 7. I bought it used in June 2025 for £150. It’s great, and I now wear it every day. Like all tech, smartwatches depreciate in value quickly. It’s best to buy a good-quality used model that’s a few years old. That’s what I did. My watch is still as-new, and I effectively got a 50% discount on the original purchase price. I intend to wear it for many years to come. It’s become a replacement for my actual watch (which I’ve had since I was 18 and is solar powered) – I’ve since given this to my Dad.
If you’re looking for one, I’d recommend Ebay (which is where I got mine), BackMarket, musicMagpie, or indeed any reputable store which sells used or refurbished models.
Use data to improve your health
I think technology is a blessing when it comes to monitoring our health. We can use it to revolutionise how we approach training, and to make our journey towards a longer, healthier life more fun and rewarding. I track several metrics daily: the duration and quality of my sleep (yes, I wear my smartwatch overnight), VO2 max, resting heart rate, heart rate recovery and daily steps taken.
Doing this daily really makes me think about how I can maintain my health. Have I walked or run enough today, or gone to the gym? Am I making sure I’m getting enough sleep? Have I had enough good quality sleep? Am I having relaxing – not stressful – evenings, that encourage good sleep? When I can see how I’m performing like this, the extra data really does motivate me to improve further.
How high should you aim for?
When it comes to measuring your overall health, VO2 max is the only metric you really need to worry about. Focus on improving this and everything else will fall into place. You should aim to get your VO2 max as high as possible. Of course, age and sex have a strong bearing on how fit you can be. One of the largest cohort studies of VO2 max was performed by Mandsager et al. (2018).
In his book Outlive, Peter Attia suggests that you should at least aim to be in the Elite threshold for your age group and sex. But ideally, you should aim to be in the Elite threshold for two age groups below you. I tend to agree. Aim high – it avoids complacency. You can always do better, and research suggests there are no negative impacts of improving VO2 max, at any level.
In conclusion
VO2 max is more than just a number — it’s the ultimate metric for measuring your health, fitness, and longevity. By tracking it regularly, you gain a clear picture of your cardiovascular efficiency and overall physical capacity, without getting lost in an overwhelming sea of metrics. Smartwatches make this simple, giving you daily insights that can guide your training, sleep, and recovery habits.
The key isn’t just to track VO2 max, but to actively work on improving it. Whether through running, cycling, strength training, or high-intensity intervals, every step you take toward boosting this metric compounds into long-term health benefits. Age and sex naturally influence your scores, but aiming high – in the Elite threshold for your age and sex (and ideally in the Elite threshold for two age groups below you) – keeps you motivated and avoids complacency.
Ultimately, focusing on VO2 max allows you to measure, manage, and maximise your health. It’s a simple, science-backed metric that gives you the greatest return on your investment in longevity.
FAQ
VO2 max measures the maximum rate your body can use oxygen during intense exercise. It’s the gold standard for cardiovascular fitness and the single strongest predictor of longevity. Higher VO2 max indicates better overall health, stamina, and endurance, reflecting the efficiency of your lungs, heart, blood vessels, and muscles working together.
VO2 max strongly correlates with lifespan and disease risk. Higher levels improve cardiovascular efficiency, muscular endurance, and metabolic health – helping you maintain independence and quality of life as you age. Tracking and improving this metric provides a clear, science-backed roadmap for long-term health.
VO2 max can be measured in a lab via treadmill or cycling tests with oxygen masks, but most people rely on smartwatches for daily estimates. Devices like Apple Watch and Garmin use heart rate and GPS data combined with algorithms to give a reliable approximation, sufficient for monitoring progress over time.
High-intensity interval training, consistent running, cycling, and strength training are effective. Gradually increasing intensity and volume over time, maintaining recovery, and monitoring your progress using a smartwatch will improve your VO2 max, enhance cardiovascular fitness, and extend both lifespan and healthspan.
Enjoy this article? If so, here are some others you may also like:
Why you need to embrace discomfort
A no-nonsense guide on how to live a healthy life
Building fitness for a longer life
The unexpected benefits of lifting heavy weights
How to get a good night’s sleep
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