If you read nothing else
Your watch isn't measuring your VO2 max. It's estimating it from your pace, heart rate and a few other inputs. It's a guess. A reasonable one, but a guess.
The number is a lagging indicator. It moves weeks after the fitness change actually happened, so refreshing it after every run tells you nothing.
You can't move it with one session. Consistent easy running, occasional hard sessions, and long easy runs over months and years is the only thing that works.
Social media has turned VO2 max into a panic metric because it gets clicks. It doesn't deserve the airtime it's getting.
Improvements get smaller the fitter you become. That's not a failure, it's physiology.
Focus on showing up, running easy most of the time, and enjoying it. The number will sort itself out.
What VO2 max actually is, in plain English
VO2 max is the maximum amount of oxygen your body can use during hard exercise. That's it. It's measured in millilitres of oxygen per kilogram of body weight per minute, which is a mouthful, so most people just talk about the number.
A higher number means your heart, lungs and muscles are better at pulling oxygen out of the air and turning it into the energy that moves you down the road. It's a reasonable proxy for aerobic fitness - useful, but not the whole picture, and absolutely not the only thing that determines whether you're a good runner or a happy one.
The proper way to measure it is in a lab, on a treadmill, wearing a mask that looks like something out of a bad sci-fi film. You run until you can't run anymore. It's not pleasant, and almost none of us have ever done it.
What your Garmin is actually showing you (and it's not VO2 max)
Here's the bit that gets glossed over. Your watch has not measured your VO2 max. It can't. It doesn't have a mask, it doesn't measure your oxygen consumption, and it has no idea what's actually happening inside your lungs.
What it's showing you is an estimate. The watch takes your heart rate, your pace, your age, your weight, maybe your heart rate variability, and runs it through an algorithm that spits out a number that's roughly in the ballpark of what your VO2 max probably is. Garmin uses Firstbeat's algorithm, Coros and Apple use their own variations, but they're all doing the same thing - guessing, based on the data they have.
It's a useful guess. It's also a guess. Treat it as such.
Why your watch's VO2 max is a lagging indicator
This is the bit that drives people mad, and it shouldn't. Checking your VO2 max after every session is a complete waste of your time, and here's why.
The number you see on your watch is a smoothed average. It doesn't move based on one run. The algorithm is specifically designed not to react to a single session - because if it did, it'd be wildly unreliable. You'd run hard one day and your VO2 max would spike. You'd run on a humid morning and it'd tank. The algorithm filters all that out by drawing on data from multiple runs over multiple weeks.
So what you're seeing is the watch's best read on what your fitness looked like a few weeks ago. By the time the number ticks up, the actual physiological change happened ages back. By the time it ticks down, you'd already lost the fitness before the watch noticed.
Refreshing it after every run is like checking the share market every five minutes. It won't tell you anything useful, and it'll do your head in.
Why obsessing over the number is wasting your time
If you're a beginner or a returning runner, your VO2 max will go up if you run consistently. That's it. That's the whole game. You don't need to monitor it, agonise over it, or screenshot it.
The thing that actually drives improvement is showing up. Easy runs, done regularly, build the engine. Checking your watch obsessively for a number to validate that won't make it happen any faster. It'll just make you anxious, and anxious runners tend to push too hard on easy days, skip recovery, and break themselves trying to force a number to move.
The number is a side effect of doing the work. Not the work itself.
Where did all the VO2 max hype come from?
A few years ago, almost nobody outside of sports science talked about VO2 max. Now it's everywhere. Why?
Two reasons, mostly. First, watches started displaying it, which gave millions of people a number they could brag about, worry about, and post about. Second, the social media algorithm noticed that anything with "VO2 max" in the title got clicks, so creators started churning out content about it. "This one drill will boost your VO2 max." "Why your VO2 max is killing your longevity." "Five foods that increase VO2 max overnight." It's a content goldmine, and the incentives are to make it sound urgent and dramatic.
It's not urgent. It's not dramatic. It's a slow-moving fitness marker that responds to the same things every other fitness marker responds to - consistent training over a long period.
"But my watch is showing a number that's way too low"
This one comes up a lot, and it usually goes like this. Someone glances at their watch, sees a VO2 max number they don't like the look of, and decides the watch must be broken. The algorithm's wrong. The strap's loose. Garmin's got it in for them personally.
Let's go back to what the watch is actually doing. It's looking at the pace you're running and the heart rate you're holding at that pace, and it's working out roughly how efficient your body is at using oxygen. That's the whole calculation. There's no conspiracy. There's no setting buried in the menu that's sandbagging your score.
If the number is consistently lower than you reckon it should be, the most likely explanation is the boring one: at the paces you're running, your heart rate is higher than someone with a higher VO2 max would have. That's not the watch being mean. That's just what the data says.
A few honest things to check before you blame the device. Is your max heart rate set correctly? The default "220 minus your age" is rough as guts and can throw the calculation off if your real max is higher or lower. Is your watch actually picking up your heart rate properly - wrist optical sensors are notoriously dodgy, especially in cold weather or during intervals, and a chest strap gives much cleaner data. Are most of your runs done at a sensible easy pace, or are you grinding every run at the same medium-hard effort that doesn't really tell the algorithm anything useful?
If you've checked all that and the number is still lower than you'd like - sit down, we need to have a chat. The watch isn't wrong. Your fitness is what your fitness is. That's not a criticism, it's just where you're starting from. The good news is the only thing that fixes it is the same thing that fixes everything else in running: showing up consistently, for a long time, without trying to shortcut the process.
The watch is a mirror. If you don't like what you see, the answer isn't a different mirror.
How to spot VO2 max engagement bait
A few tells. Anyone promising a specific percentage increase from a single workout is selling you something - usually attention, sometimes a programme. Anyone framing VO2 max as the single most important number for your health is overstating it. Anyone implying that you can shortcut years of training with a six-minute reel is either confused or deliberately misleading you.
The format gives it away too. Big number in the thumbnail. Dramatic music. A bloke on a treadmill pointing at a graph. "I tried this for 30 days and you won't believe what happened." If that's the energy, close the app and go for an easy run.
How to actually improve your VO2 max
The boring, real answer.
Run easy, consistently. Most of your running - the vast majority - should be at a pace where you can hold a conversation. This builds your aerobic base, which is the foundation everything else sits on. Without it, the hard stuff doesn't work.
Add hard sessions, but only when you've earned them. Intervals at around 5k pace or slightly faster, with proper recovery between them, are what physiologically push VO2 max up. But they only work if your easy running has built the base to support them. Doing hard sessions on top of nothing is how you get injured.
Long, easy runs. A weekly longer run at a comfortable pace builds capacity in a way short runs can't. It's not about pace. It's about time on feet.
Repeat for months. Then years. That's it.
The annoying truth: diminishing returns
When you're new, your VO2 max can climb quickly. A previously sedentary person who starts running consistently might see big jumps in the first six to twelve months. It's encouraging, and it's real.
After that, it slows down. A lot. The fitter you get, the harder you have to work to move the number even slightly. A trained runner trying to add a single point to their VO2 max might need months of focused, structured training - and even then, there's a ceiling set largely by genetics that you can't bully your way past.
This is normal. It's not a failure. It's just how physiology works. If you've been running for years and your VO2 max has plateaued, you haven't done anything wrong. You've just arrived at the part of the curve where progress is measured in patience.
So what should you actually focus on?
How your runs feel. Whether you're getting out the door regularly. Whether you're enjoying it. Whether you're sleeping well, recovering properly, and free of niggles. Whether you can run for longer, or at the same pace with a lower heart rate, or finish a session and feel good instead of wrecked.
These are the things that matter. The VO2 max number on your watch is a downstream consequence of getting those things right. Get the inputs right, ignore the number, and one day you'll glance at your watch and notice it's gone up without you noticing.
That's how it's meant to work.