VO2 max is the most oxygen your body can take in and use per minute at full effort, measured in millilitres per kilogram of body weight per minute (ml/kg/min). It sets the ceiling on your aerobic engine, and in the first scientific study of HYROX, athletes with a higher VO2 max finished faster.
There are two numbers that get called your VO2 max, though. One is the estimate your watch gives you. The other is the one your race results imply, and for a runner that second number is the more useful one, because it turns straight into race times and training paces. This guide covers both: what a good VO2 max is for your age, why the two numbers disagree, and the training that moves them.
Key Takeaways
- The median treadmill VO2 max is 48.0 ml/kg/min for men and 37.6 for women in their twenties, falling to 24.4 and 18.3 in their seventies (FRIEND registry).
- A watch estimates VO2 max rather than measuring it: one 2025 validation found an average error of about 7% against lab tests, so read it as a trend.
- A race result gives you a VDOT, Jack Daniels’ running fitness number: a 20:00 5K works out to about 50, which predicts a 10K of about 41:30.
- In the first HYROX study, a higher VO2 max and more endurance training volume both went with faster finish times.
- Intervals of three to five minutes at 90 to 95% of maximum heart rate raised VO2 max more than steady running in a controlled eight-week trial.
What Is VO2 Max?
VO2 max is your maximal oxygen uptake: the highest rate at which your heart, lungs and muscles can deliver and use oxygen during exercise. It is written in ml/kg/min so that people of different sizes can be compared. A 70kg runner with a VO2 max of 50 uses 3.5 litres of oxygen a minute at full effort.
Think of it as the size of the engine. How fast you actually race also depends on two more things:
- Threshold: The share of your VO2 max you can hold for a long time before fatigue builds quickly. It decides how much of the ceiling you can use in a race lasting an hour.
- Economy: How much oxygen you burn at a given pace. A more economical runner goes faster on the same oxygen.
This is why two runners with the same VO2 max can finish a 10K minutes apart. The ceiling sets what is possible; threshold and economy decide how much of it shows up on race day. Our guide to the HYROX engine goes through all three parts for a HYROX race.
What Is a Good VO2 Max by Age?
A good VO2 max is one above the median for your age and sex. The largest published reference set for treadmill tests, the FRIEND registry (Kaminsky et al., Mayo Clinic Proceedings, 2015 ), puts the median for men aged 20 to 29 at 48.0 ml/kg/min and for women at 37.6. A value at the 75th percentile or higher is clearly above average.
The table below shows the 50th, 75th and 90th percentiles from that registry, by decade. These are lab tests on a treadmill, not watch estimates.
| Age | Men 50th | Men 75th | Men 90th | Women 50th | Women 75th | Women 90th |
|---|---|---|---|---|---|---|
| 20-29 | 48.0 | 55.2 | 61.8 | 37.6 | 44.7 | 51.3 |
| 30-39 | 42.4 | 49.2 | 56.5 | 30.2 | 36.1 | 41.4 |
| 40-49 | 37.8 | 45.0 | 52.1 | 26.7 | 32.4 | 38.4 |
| 50-59 | 32.6 | 39.7 | 45.6 | 23.4 | 27.6 | 32.0 |
| 60-69 | 28.2 | 34.5 | 40.3 | 20.0 | 23.8 | 27.0 |
| 70-79 | 24.4 | 30.4 | 36.6 | 18.3 | 20.8 | 23.1 |
The decline with age is steep, roughly four to six points per decade in men, so the right comparison is always with your own age group. And the 90th percentile at 40 to 49 is higher than the median at 20 to 29, which is what years of consistent endurance training look like on paper.
What Counts as Good for a Runner or HYROX Athlete
The registry is a general reference sample, not a group of athletes, so for someone who trains for races the median is a low bar. If you run or race HYROX regularly, the 75th and 90th percentile columns for your age are the fairer comparison.
For an athlete, two questions matter more than the ranking: is your number rising, and what does it mean for your race pace? That second question is where the race-based number comes in.
Your Watch’s VO2 Max Is an Estimate
A watch does not measure VO2 max. It estimates it from the relationship between your heart rate and your running pace (or cycling power) on steady efforts, using a model calibrated against lab tests. A lab test measures the oxygen and carbon dioxide in your breath while the treadmill gets harder until you stop.
Independent studies have found the estimates are reasonable but not exact. A validation of the Garmin Fēnix 6 against lab tests found a mean absolute error of about 7% (a 2025 validation study ). On a VO2 max of 50, 7% is 3.5 points, about the gap between two rows in the table above.
Three things make a watch estimate more useful:
- Set your real maximum heart rate. The models lean on it. An age-based maximum that is 10 beats too low will skew the number.
- Wear a chest strap if you have one. A strap reads heart rate more accurately than a wrist sensor, and a bad heart-rate trace makes a bad estimate.
- Watch the trend, not the reading. A two-point rise over three months of steady training means more than any single figure.
Take Priya, 34, who runs a 22:30 5K and sees 47 on her watch. That is well above the 90th percentile for women her age (41.4), which is true and pleasant to know. But 47 does not tell her what pace to run her intervals at, or what her 10K should be. Her 5K does.
VO2 Max and Race Prediction: The Number Your Races Give You
Your race times imply a fitness number of their own, called VDOT. Jack Daniels and Jimmy Gilbert built it from two curves: how much oxygen a given running speed costs, and what share of your VO2 max you can hold for a given time. Put a race result in and you get a single number in the same units as VO2 max, which you can then turn into a time at any other distance.
VDOT is not a measured VO2 max. It is your running fitness, expressed as if it were one. That is exactly what makes it useful: it already includes your economy and your threshold, because it comes from how fast you actually ran.
Here is what three 5K times give you, worked through the same model the race time predictor uses. Riegel’s formula and the Daniels curves are shown side by side, because they disagree a little and the disagreement is worth seeing.
| 5K | VDOT | 10K (Riegel / Daniels) | Half (Riegel / Daniels) | Marathon (Riegel / Daniels) | Pace at VO2 max |
|---|---|---|---|---|---|
| 25:00 | 38.3 | 52:07 / 51:53 | 1:55:00 / 1:55:04 | 3:59:47 / 3:57:55 | 4:45 per km |
| 22:30 | 43.4 | 46:55 / 46:40 | 1:43:30 / 1:43:27 | 3:35:48 / 3:34:43 | 4:18 per km |
| 20:00 | 49.8 | 41:42 / 41:28 | 1:32:00 / 1:31:50 | 3:11:49 / 3:11:17 | 3:51 per km |
The last column is the pace at which the Daniels oxygen-cost curve reaches your VDOT: in that model, the speed you could hold flat out for about 11 minutes. It is the pace the interval sessions further down are built around. So for Priya, the useful number is 43.4 and a rep pace near 4:18 per kilometre, not the 47 on her wrist.
A prediction assumes you have trained for the distance. A 20:00 5K runner who never runs longer than 10km will not run a 3:11 marathon. The prediction tells you what your engine allows, not what your legs are ready for.
One Runner, Three Different Numbers
Niels Post, Kracey’s founder, has a 1:16 half marathon, a 2:45 marathon and a 17:22 5K best. Put each through the same model and you get a VDOT of about 62 from the half, 59 from the marathon and 59 from the 5K.
From the half alone, the model predicts a 5K of about 16:30, nearly a minute faster than he has run. His own read: “either the half is flattering me or I just haven’t raced a 5K properly.” Both are possible, and that is the point. Your best race at any distance is the most honest estimate you have, so use your strongest recent result, and treat a prediction for a distance you have not raced as a ceiling, not a promise.
Why VO2 Max Matters in HYROX
VO2 max matters in HYROX because the race is mostly running. In the first scientific study of HYROX (Brandt et al., Frontiers in Physiology, 2025 ), 11 recreational athletes did a simulated race after a lab VO2 max test. The runs took a median 51.2 of their 86.5 minutes, and athletes with a higher VO2 max finished faster, as did those with a greater volume of endurance training.
The authors concluded that HYROX places its emphasis on endurance capacity, with moderate to low demands on maximal strength. It was a small study, so treat it as a first look rather than a final word. But it fits what the race asks: 8km of running, eight stations that keep your heart rate high, and the Roxzone between them, for an hour or more.
A high ceiling helps HYROX athletes in two ways:
- The runs cost less. At a given pace you are working at a smaller share of your maximum, so you arrive at each station with more left.
- You recover faster between efforts. After a sled push sends your heart rate to the top, a bigger engine brings you back to race pace sooner, which is the heart of compromised running .
Niels ran his 56:18 HYROX with runs at 3:38 per kilometre, within two seconds of his half marathon pace. For him, each HYROX run is close to a half marathon effort, repeated eight times with a station after each one.
How to Improve VO2 Max
You improve VO2 max mainly with hard intervals of three to five minutes, run close to your maximum, on top of a base of easy running. Most athletes see it move over six to 12 weeks of consistent work, and the gains slow as you get fitter.
Intervals Close to Your Maximum
The best-known trial is Helgerud et al. (2007) . Forty moderately trained men trained three times a week for eight weeks. The two groups who ran intervals at 90 to 95% of maximum heart rate (4 x 4 minutes, or 15 seconds on and 15 off) improved VO2 max significantly more than the groups who ran steadily at 70% or at threshold.
A meta-analysis of 37 interval studies (Bacon et al., PLoS One, 2013 ) found an average rise of about half a litre of oxygen a minute over six to 13 weeks, with larger gains in the studies that used longer intervals.
Sessions that work, at roughly the “Pace at VO2 max” column above:
- 4 x 4 minutes with 3 minutes of easy jogging between reps.
- 5 x 1,000m with 2 to 3 minutes of easy jogging.
- 6 x 3 minutes with 3 minutes easy.
By the end of each rep your heart rate should be near its maximum. If you train by zones, that is the top two (Z4 and Z5); the training zone calculator gives you your numbers. HYROX athletes can do some of these on the rowing machine or the SkiErg, which work the same system and spare the legs.
Keep the Easy Volume Under It
Intervals raise the ceiling, but easy running is what lets you absorb them. Niels describes it as a pyramid: “if you want to build a high pyramid, so you want to have a crazy fast zone 4, zone 5 … You need to also have like a wide base. And the way to build a wide base is zone 2.”
In practice, keep one VO2 max session a week, two at most in a build, and make most of your other running easy enough to hold a conversation. Our guide to HYROX training zones explains how to set the easy ceiling.
Progress the Session, Not the Pace
When a session gets easier, add a rep or cut the recovery before you run the reps faster. Your rep pace should only change when a new race result says your VDOT has moved. Running intervals faster than your fitness allows turns a VO2 max session into an anaerobic one, and you finish it tired rather than fitter.
How Fast VO2 Max Moves
Expect the biggest gains in your first months of structured training, then smaller ones. Responses vary widely between people: the Bacon meta-analysis found large differences between studies, and some athletes respond to the same plan much more than others. If your watch number stalls, check your race times before you change anything. A faster 5K is the result you were training for anyway.
FAQ
Above the median for your age and sex. In the FRIEND registry the median for men is 48.0 ml/kg/min at 20 to 29, 42.4 at 30 to 39 and 37.8 at 40 to 49; for women it is 37.6, 30.2 and 26.7. The 75th percentile is clearly above average.
Roughly. One 2025 validation found an average error of about 7% against lab tests, and accuracy depends on the device and on whether your maximum heart rate is set correctly. Use it to track change over months, not as an exact figure.
VO2 max is the oxygen you can use per minute, measured in a lab or estimated by a watch. VDOT is a running fitness number calculated from a race result with the Daniels and Gilbert model. It uses the same units but also includes your economy and threshold, so it predicts race times better.
Most interval studies run six to 13 weeks and find clear gains in that time. With one or two hard sessions a week on top of easy running, expect a measurable change within about two months, then slower progress.
Yes. In the first scientific study of HYROX, athletes with a higher VO2 max and more endurance training finished faster, and running made up more than half of the race time. It was a small study of 11 athletes, and strength still matters on the stations.
Intervals of three to five minutes at 90 to 95% of maximum heart rate, such as 4 x 4 minutes with 3 minutes of easy jogging between reps. Do one a week on top of a base of easy running, and add reps before you add pace. ---
Train the Engine You Actually Have
VO2 max sets your aerobic ceiling, and a good VO2 max is one above the median for your age. Your watch gives you a fair estimate to track over months, and your race results give you a VDOT, which turns straight into predicted times and the pace for your intervals. In HYROX, the evidence so far says the engine matters more than maximal strength. To raise it, run intervals of three to five minutes near your maximum once a week, keep the rest of your running easy, and let a new race result tell you when to run faster.
Your Kracey coach reads your daily data from intervals.icu, including the VO2 max estimate when your watch provides one, alongside your sleep, HRV and resting heart rate, and it judges your interval sessions from the lap splits rather than the average. It lives in Telegram and messages you first. Get coached in Telegram : 14 free days, no card, and they start when your coach can see your training, because a coach that cannot see you is not coaching you.