VO2 max: what it measures and how to improve it
VO2 max is the most oxygen your body can use during hard exercise. What mL/kg/min means, lab tests vs watch estimates, and how to raise yours.
What is VO2 max?
VO2 max is the highest rate at which your body can take in and use oxygen during all-out exercise. It is usually expressed in milliliters of oxygen per kilogram of body weight per minute (mL/kg/min) and is the standard lab measure of cardiorespiratory fitness. Labs measure it with a mask on a treadmill or bike. Watches estimate it from heart rate and pace.
As you run or cycle harder and harder, the oxygen your body uses climbs with the effort, until it can’t climb any further. That ceiling is VO2 max. It depends on how much blood your heart pumps with each beat, how much oxygen your blood carries, and how well your muscles pull that oxygen out and use it.
What the number means
VO2 max is usually reported relative to body weight, in mL/kg/min, so people of different sizes can be compared. You get it by dividing the oxygen used per minute by body weight. A 70 kg runner who uses 3.5 liters of oxygen per minute at maximum has a VO2 max of 3,500 ÷ 70 = 50 mL/kg/min. At 65 kg, with the same 3.5 liters, the same runner would read about 54.
Values vary widely. Men tend to test higher than women on average, VO2 max tends to decline with age, and training raises it at any age. Elite endurance athletes often test above 70 mL/kg/min. The most useful comparison is with your own past readings. The American Heart Association made the case in a 2016 scientific statement that cardiorespiratory fitness should be assessed routinely in clinical practice, much like a vital sign.
Lab tests vs watch estimates
| Method | How it works | Accuracy |
|---|---|---|
| Lab test | A graded test to exhaustion on a treadmill or bike, wearing a mask that measures the oxygen you breathe in and the carbon dioxide you breathe out. | The reference standard. |
| Field test | A timed all-out effort, such as the Cooper 12-minute run, plugged into a formula. | A reasonable estimate if you pace it well and push hard. |
| Watch estimate | The watch compares your heart rate with your pace or power during outdoor walks, runs or rides. | Good for following a trend. A single reading can be noticeably off. |
The Cooper test, published by Kenneth Cooper in 1968, asks you to cover as much distance as you can in 12 minutes. A common formula estimates VO2 max as (distance in meters − 504.9) ÷ 44.73. Cover 2,800 meters and the estimate is about 51 mL/kg/min.
Watches need good data to make a good estimate. Apple Watch, for example, estimates VO2 max (it calls it cardio fitness) during outdoor walks, runs and hikes. Most watches need several workouts before the number settles, and a correct age, weight and maximum heart rate in your profile help.
How to improve VO2 max
Most of the gains come from two kinds of aerobic work, kept up for weeks and months.
- Easy volume: Plenty of running, cycling, rowing or brisk walking at a pace where you can still hold a conversation. It builds the base that harder work rests on.
- Intervals: Repeated hard efforts with easy recovery in between. One well-studied format is four 4-minute efforts at about 90–95% of maximum heart rate, with 3 minutes of easy movement between them.
- Consistency: Two or three cardio sessions a week, kept up for months, beats one hard month followed by nothing.
- Body composition: Because the number is per kilogram, carrying less body fat raises relative VO2 max even if your heart and lungs haven’t changed.
People starting from a low base usually improve fastest. Trained athletes improve slowly, because they’re closer to their ceiling, and genetics set much of that ceiling. Two people on the same plan can respond very differently. If you have a heart condition, or get chest pain, dizziness or unusual breathlessness during exercise, talk to a doctor before all-out tests or hard intervals.
Common mistakes
- Treating a watch reading as a lab result: It’s an estimate. Follow the trend over months, not the number from one run.
- Only doing intervals: Hard sessions work best on top of a base of easy aerobic training.
- Comparing across brands: Two watches can give the same person different numbers.
- Expecting fast change: Meaningful improvement usually takes weeks to months of consistent training.
How FORM uses it
FORM reads VO2 max from Apple Health or Health Connect when your watch records it, alongside resting heart rate, HRV and sleep. FORM doesn’t estimate VO2 max itself and has no GPS tracking of its own. Runs, rides and walks recorded on your watch are imported into the workout tracker, next to your strength sessions. To set up an Apple Watch, see Apple Watch and Apple Health.
FAQ
What is a good VO2 max?
It depends heavily on age and sex, so the most useful comparison is with your own past readings. Elite endurance athletes often test above 70 mL/kg/min.
How accurate is VO2 max on Apple Watch?
It’s an estimate from heart rate and pace during outdoor workouts. It’s useful for following a trend over months, but a single reading can differ from a lab test.
How long does it take to improve VO2 max?
Most people see measurable gains within several weeks of consistent aerobic training. The biggest improvements come in people starting from a low base.
Does strength training improve VO2 max?
Lifting can raise it a little, mainly in people who were untrained. Endurance work and intervals are the main drivers.