Fitness · topic 4 of 5
How accurate each test is
What r ≈ 0.90 means, what the stars mean, and where each test stops working
- Lab test, direct
- measuredGas analysis. The only one that measures rather than estimates.
- 12-minute run
- r ≈ 0.90Strong, if you truly go all out. Pacing conservatively under-reads you.
- 6-minute walk
- submaximalBuilt for lower fitness. It under-reads a fit person by design.
- Watch estimate
- 7 to 16 % errorCarried with every wearable reading Verve shows. Never the headline.
The r value
Every test in Verve carries a small badge —r ≈ 0.90on the Cooper run, for instance. r is a correlation coefficient: how closely the test’s estimate tracks a true VO₂Max measured in a laboratory with a gas-analysis mask. It runs from 0 (no relationship at all) to 1 (a perfect one).
An r of 0.90 means the test ranks people almost exactly as the lab would. Someone it puts above you would almost certainly test above you on a treadmill. What r does not tell you is how far off any single number is — a test can rank a whole group perfectly and still read a few points high for everyone in it. That is why the honest use of a field test iscomparing you against yourself over time, on the same test, rather than treating one result as a laboratory measurement.
| Test | Effort | Accuracy |
|---|---|---|
| Bruce Protocol | Maximal, supervised | ±3.5 mL/kg/min |
| Cooper 12-Minute Run | Maximal | r ≈ 0.90 |
| 1.5-Mile Run | Maximal | r ≈ 0.85 |
| 1-Mile Walk Test | Submaximal | r ≈ 0.88 |
| 6-Minute Walk Test | Submaximal | ~13% MAPE |
MAPE is mean absolute percentage error — the average size of the miss, regardless of direction. It answers the question r cannot.
The stars
The star rating is Verve’s own shorthand for how much weight a result deserves, and it combines two things the r value keeps separate: how well the method is validated, and how much of the answer depends on you performing well on the day. Four stars are the maximal tests, where the number is limited by your physiology. Three stars are the submaximal ones, which estimate your capacity from how your heart responds to easy work — safer, repeatable, and one inference further from the thing being measured.
Where these tests stop working
Field-test estimates are most accurate for active-to-trained young and middle-aged adults, because that is who the validation studies recruited. They are less reliable at both edges: highly trained athletes, whose results compress near the top of the scale, and very sedentary people, who are under-represented in the original data and whose pacing on an unfamiliar all-out effort is itself unpractised. If you sit at either edge, the trend in your own numbers is worth more than any single one of them.