Watch metric
VO2 Max
VO2 Max Definition
An estimate of how much oxygen your body can use at full effort - a rough proxy for your aerobic fitness.
The figure is meant to indicate: the amount of oxygen you can use, per minute, per KG of body weight.. Obviously, your watch doesn't know this, so it has to estimate.
The actual formula used by watch manufacturers isn't public, but in general, we can assume that they use a mix of your heart rate at different paces, compared to the known, tested VO2 Max of other people who's numbers line up closely.
For example, if you run at the same pace, with the same heart rate as someone who was tested to have a VO2 Max of 50, then the watch may put you in that ballpark.
We can also assume most watches take into account elevation or heat, but it's not confirmed.
A higher VO2 Max generally indicates a higher level of fitness and is often coupled with faster times, but it's not guaranteed.
Does a high VO2 Max mean you can run faster?
No, VO2 Max is a measure of how efficiently your lungs and muscles consume oxygen when maxed out. It is not a measure of how fast you can run at that maximum efficiency.
Speed at VO2 Max is a different metric and is the one that actually says how fast you run at maximum capacity.
You can max out your lungs and muscles at a pretty slow pace if you tried to crawl on all fours for example.
It is often compared to an engine capacity, it gives you an idea of raw aerobic power, but not the speed at which you end up going at full power.
18 Wheeler Trucks often have bigger engine capacities than sports cars for example, but they're not faster because they're far less efficient with all that power.
To show that this metric has caveats, simply look at it's definition. Your body weight in KG is part of the formula, so simply losing weight will increase your VO2 Max because the ml of oxygen used per minute is divided by a lower number.
Key VO2 Max things to know
- Your watch does not actually know your VO2 Max, it is estimating based on what it knows about you.
- Trying to trick your watch, or do specific workouts with the sole aim of increasing the VO2 Max figure, is a waste of your time
- Checking your VO2 Max after each run is an actual waste of time. Train consistently and it'll go in the right direction.
When it helps
As a slow-moving trend over months. A gentle climb means your training is working.
When it doesn't
As a day-to-day measure or something to check after each run. It lags weeks behind and reacts to nothing you did this morning.
The common myth
The myth: your watch measures your VO2 max. The reality: it estimates it from pace and heart rate, and the number can be well off.