A higher VO₂max number on your watch is a changed estimate. By itself, it does not establish a fitness gain. The relevant question is whether the method reliably detects change in the same person. A study can find agreement with a laboratory measurement without answering that separate question.

VO₂max means maximal oxygen uptake. The watch discussed here estimates it from running data; the researchers obtained the comparison value through respiratory gas analysis during a treadmill test. Both values use the same unit: millilitres of oxygen per kilogram of body mass per minute, or ml/kg/min. A shared unit does not make the methods equivalent.

What the 2025 study actually tested

Florian A. Engel, Lukas Masur, Billy Sperlich and Peter Düking published their investigation on 6 August 2025 in the European Journal of Applied Physiology. It was a comparative validation study with repeated watch measurements. The sample included 35 trained endurance athletes from running and triathlon: 24 men and 11 women, with a mean age of 25.1 years.

The laboratory visit included a treadmill test with respiratory gas analysis and a verification phase. Participants then completed two 15-minute runs, separated by 48–72 hours. A Garmin Forerunner 245 running software version 13.00 estimated VO₂max. These were repeated watch estimates against one laboratory assessment, rather than laboratory measurements before and after a training period.

In “Results → All athletes” and Figure 3B (printed page 597), the watch estimate after the second run was 4.05 ml/kg/min below the laboratory value on average. The reported 95% limits of agreement ranged from −12.02 to +3.93 ml/kg/min. These limits describe the spread of differences between watch and laboratory in this sample. They are neither your personal error interval nor a threshold above which a later watch increase counts as real. Study results and Figure 3, also on PDF page 7.

The average underestimation is not a correction factor for your watch either. Adding 4.05 to your own value would treat a group average as your individual error.

Matching a laboratory value and detecting progress are different questions

A validation study asks: how close is an estimate to the comparison method under the conditions tested?

For training progress, the question becomes: does a change in the watch estimate follow a measured change in the same person? Answering that requires repeated comparison measurements over a suitable period, such as before and after a training phase.

Engel and colleagues did not include a training block with those before-and-after laboratory measurements. The two short runs therefore do not establish how reliably the watch detects fitness gains over weeks. That is a limit of the design, not evidence that every change is merely measurement noise.

Synthetic example: a watch shows 50 and later 52 ml/kg/min. The displayed estimate has increased by two units, or four per cent. That establishes a change in the display. Whether maximal oxygen uptake also increased by four per cent remains unresolved without suitable comparison evidence. This study's limits of agreement do not settle that question.

What makes a weekly comparison understandable

A short context note is more useful for your training record than an unsupported declaration of progress:

  • Where did the value come from? Record the watch model, date and known changes to the device or profile. Garmin's Forerunner 245 instructions identify the user profile and maximum heart rate as inputs for the most accurate estimate. They also explain that the device initially needs several runs.
  • Are the observations comparable? Record the route, surface, weather, stops and heart-rate source where known. These notes reveal differences; they do not supply a universal numerical correction for the watch value.
  • What else was recorded? Describe completed sessions, time or distance and perceived effort. Identify missing information. Several recordings from the same watch are not independent confirmation of its method.

For the example, a suitable note would be: “The watch estimate rose from 50 to 52. The runs and device settings are only partly comparable. This does not establish a change in laboratory-measured VO₂max.” It preserves the observation without claiming more than the data support.

NuroStride's methods page describes weekly reviews and reproducible training-load calculations. Its assistant is instructed to ask about missing information. The kit includes no ready-made watch connection or implemented performance forecast. These functions do not independently validate a VO₂max estimate.

Who the finding applies to

The sample was small, young and already trained. The researchers planned for 79 participants and studied 35. Women were less represented. The findings concern one watch model, one software version and a controlled running protocol. They cannot simply be transferred to older recreational runners, other devices or current firmware. They also do not establish NuroStride's effectiveness or guarantee a race time.

The evidence supports a bounded conclusion: treat the number as an estimate with recorded context. A rise can prompt a closer look at your records. Claiming a demonstrated fitness gain requires additional evidence suited to that question. The watch value supplies no medical assessment or clearance to train.

Sources checked on 11 October 2026. The report gives second-run mean absolute percentage error as 7.2% in the abstract (printed page 591), but 6.7% in Table 4 and the discussion (page 599) and conclusions (page 601). We therefore use neither percentage as an accuracy claim. The whole-cohort bias agrees between the abstract and results, and Figure 3B supports its sign and agreement limits. Inconsistent subgroup and heart-rate recording details also limit interpretation. No personal correction or change threshold follows from these results. This is an interpretation of one study, not a statement of scientific consensus.