What's the Difference Between VO2 Max and VO2 Peak?

VO2 max is the most oxygen the body can take up and use, confirmed by a plateau: oxygen uptake stops rising even as the exercise keeps getting harder. VO2 peak is simply the highest oxygen uptake reached during a test, whether or not that plateau showed up. In healthy adults giving a full effort, the two usually land on the same number: in a 2003 laboratory study of 71 adults, a clear plateau appeared in only 12, yet the peak values matched those from extra confirmation tests. The difference is mostly about proof, it matters more in special and clinical groups, and the main US reference tables have used both names for the same kind of measurement.

VO2 max and VO2 peak side by side

Both are measured the same way, by analyzing breathed air during an exercise test that gets harder until the person stops, and both are reported in milliliters of oxygen per kilogram of body weight per minute.

Why the plateau so often fails to show up

The textbook picture of a VO2 max test ends with oxygen uptake flattening out while the workload climbs. In practice that flat line is often missing. In a 2003 study of 71 adults on a ramp cycling test, oxygen uptake fell short of its expected trajectory, a plateau, in 12 of them, ran above it in 19, and could not be told apart from it in the remaining 40 (Journal of Applied Physiology, 2003).

The peak values were still sound. They did not differ from the value reached in a single all-out constant-load test in 38 of the participants, or from a true VO2 max established with a series of separate tests in 6 of them. The authors concluded that the peak from a full-effort test is likely a valid index of VO2 max even without a plateau, adding that without extra tests no one can be certain.

Checking with a verification test

Some laboratories add a verification phase: after the main test, a short, hard bout, often at a workload above the one where the person stopped. If oxygen uptake does not climb higher, the earlier peak was the ceiling.

In healthy adults that check rarely changes the answer. A meta-analysis of 54 studies, drawn from 80 covering 1,680 people aged 19 to 68, found the highest oxygen uptake in the main test and in the verification phase essentially identical, a mean difference of 0.03 liters per minute that was not statistically significant. Sex, fitness level, treadmill or bike and the type of verification protocol made no difference (PLOS ONE, 2021).

In special and clinical groups the average still matched. A second meta-analysis of 30 studies found no difference between the main test and verification phase at the group level. Individuals were a different story: across the studies that reported it, the share of participants who reached a higher value on verification ranged from 0 to 88.9 percent, and the authors judged that more participant-level data is needed before guidelines can be set (PLOS ONE, 2024). For one person in one of these groups, a peak may sit below the true maximum.

Which one the age tables report

Both, depending on the year. The FRIEND registry's first US reference standards, from 7,783 treadmill tests in adults aged 20 to 79 without cardiovascular disease, called their values VO2 max and counted a test as maximal when the respiratory exchange ratio, a breath-gas marker of effort, reached at least 1.0. Median values fell from 48.0 for men and 37.6 for women in their 20s to 24.4 and 18.3 in their 70s (Mayo Clinic Proceedings, 2015).

The 2022 update, built from 22,379 tests in adults aged 20 to 89, reported the same kind of measurement as peak oxygen consumption. It defined maximal effort as a respiratory exchange ratio of at least 1.0 or at least 1.1 and found mean values similar under either cut-off. Its treadmill standards came out 1.5 to 4.6 points lower than the 2015 set (Mayo Clinic Proceedings, 2022).

The table on VO2 max by age carries a median of 24.4 for men in their 70s, the 2015 figure. A VO2 peak result from a clinic or a study can be read against it the same way, keeping in mind the newer standards sit slightly lower.

Where a watch's VO2 max fits

A smartwatch's VO2 max is neither. It is an estimate of the laboratory value, calculated from heart rate and pace or power during ordinary workouts, with no breath-gas analysis at all. How the estimate is built is on how wearables estimate VO2 max, and how far it lands from a laboratory test is on estimated VO2 max accuracy.

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