VO2 max estimate is a wearable-derived approximation of maximal oxygen uptake — the volume of oxygen the body can use per minute per kilogram of body weight at peak exertion, in mL/kg/min. Apple Watch estimates cardio fitness during outdoor walk, run, and hike workouts, while Garmin, Whoop, and Polar may infer VO2 max or cardio fitness from device-supported walking, running, or cycling contexts. It is one of the most predictive long-run biomarkers for all-cause mortality and functional capacity, which is why it shows up relentlessly as "the single metric to drive up" in longevity conversations.
Why it matters
VO2 max is slow-moving (weeks to months) and relatively robust to daily noise, which makes it a better candidate for tracking the combined effect of a training and supplementation protocol than any night-to-night signal. Attia's "top quartile for your decade" framing is the useful target for most people, because it maps mortality curves to something actionable. A 30-something man moving from 38 to 45 mL/kg/min across 12 months is a meaningful change in projected functional capacity, not a vanity metric.
Reference ranges
Approximate "good" levels from consumer wearable data, aligned with ACSM norms. Units are mL/kg/min throughout.
| Age | Sex | Below average | Average | Strong |
|---|---|---|---|---|
| 20–29 | Men | < 42 | 42–51 | ≥ 52 |
| 20–29 | Women | < 36 | 36–43 | ≥ 44 |
| 30–39 | Men | < 39 | 39–47 | ≥ 48 |
| 30–39 | Women | < 34 | 34–41 | ≥ 42 |
| 40–49 | Men | < 35 | 35–43 | ≥ 44 |
| 40–49 | Women | < 31 | 31–38 | ≥ 39 |
| 50–59 | Men | < 31 | 31–39 | ≥ 40 |
| 50–59 | Women | < 28 | 28–34 | ≥ 35 |
| 60+ | Men | < 28 | 28–35 | ≥ 36 |
| 60+ | Women | < 25 | 25–32 | ≥ 33 |
The top-quartile line — roughly the "strong" column — is what most Attia-influenced protocols aim for.
What actually moves it
Zone-2 cardio 3–5 hours per week plus one weekly high-intensity interval session is the consistently effective protocol. Supplements move the needle far less, but creatine monohydrate (5 g/day), beta-alanine (3–5 g/day), and citrulline malate (6–8 g pre-session) have evidence for training-quality support that compounds over months by letting users train harder and recover faster. Any claim of "raising VO2 max" without a training stimulus should be treated at the mechanism of action rather than outcome tier — a pattern common enough to get its own write-up in supplement stack mistakes to avoid.
Device vs. lab
Lab VO2 max is measured with indirect calorimetry on a graded treadmill or cycle ergometer test, capturing actual inhaled and exhaled gas. Wearable VO2 max is estimated from heart-rate response at submaximal effort, then extrapolated. The results track reasonably well — typical wearable estimates land within 10–15% of lab values for most people — but wearables systematically underestimate for highly trained users and overestimate for sedentary ones.
| Context | Lab VO2 max | Wearable estimate |
|---|---|---|
| Purpose | Absolute number for clinical or research use | Trend line for personal training review |
| Best for | One-off benchmarking, athlete assessment | Month-over-month progress |
| Accuracy | ±3% with proper protocol | ±10–15% on absolute value; better on direction |
| Cost | $150–$400 per session | Included with the device |
| Best use pattern | Annual or semi-annual benchmark | Weekly/monthly trend |
If a single absolute number matters — a research study enrollment, a cardiac rehab program — get the lab test. For a year-over-year training check, a consistent wearable is fine.
Measurement notes
Treat a 1–2 mL/kg/min wearable shift as noise; a 3–5 mL/kg/min sustained shift across 8+ weeks is likely real. Running-derived estimates tend to be more stable than cycling-derived on devices that support both because heart-rate-to-oxygen ratios are better characterized for running. Outdoor GPS-tracked runs produce cleaner estimates than treadmill efforts on most consumer devices.
How this appears in Unfair
VO2 max estimate is available as a long-horizon objective proxy for stacks with longevity, cardiovascular, or endurance goals. It is charted against the moving average window to filter out single bad-run estimates. Because it is a slow marker, recommendation ranking weights near-term biomarkers more heavily when evaluating a new stack, and the chart sits beside resting heart rate and HRV baseline trends as part of the advanced capabilities on the review screen.
Clinical safety note
A sudden drop in VO2 max estimate paired with exertional symptoms — chest pain, disproportionate breathlessness, lightheadedness — is a cardiology conversation rather than a supplement question. A slow drift downward in an older sedentary adult that continues despite training is also worth discussing at the next physical.