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Metric

VO2 Max

What counts as a good VO2 max for your age, how much to trust your watch's estimate, and why it matters.

VO2 max is the closest thing a wearable gives you to a single fitness number, and it's one of the more researched metrics for long-term health. Your watch only estimates it, with varying accuracy. Here's what's normal for your age, how the estimate is made, and what the research connects it to.

What your device actually calls this
Scientific measurementMaximal oxygen uptake during exercise, in ml/kg/min. The lab gold standard requires a supervised treadmill/bike test with expired-gas analysis, which no consumer wearable does.
DeviceWhat they call itWhat it actually measures
Apple Watch"Cardio Fitness" (a branded name, not the scientific term)Estimated from walking/running heart rate data, per Apple's own published technical paper. Classified into four tiers (Low/Below Average/Above Average/High), not a raw number by default.
Garmin"VO2 Max" (keeps the scientific term directly)Firstbeat Analytics algorithm, analyzing the heart rate-to-pace relationship during outdoor runs/walks.
Fitbit"Cardio Fitness Score"Tracks the relationship between running pace and heart rate during a run, compares that against resting heart rate, then benchmarks the result against age, sex, and weight norms.
RingConn"VO2 Max"Added via a 2025 app update, estimated from heart-rate response during a run or walk plus age, weight, and gender.
Ultrahuman Ring"VO2 Max"Calculated from age, gender, mobility level, max heart rate, resting heart rate, and body weight, an inputs-and-formula approach rather than a dedicated test.
Coros"Fitness Level"Estimated via Coros's own EvoLab engine rather than the licensed Firstbeat algorithm Garmin uses. Methodology is unpublished; no independent validation was found.
Polar Vantage"Polar Fitness Test"Estimated at rest from heart rate, no exercise required. A 2025 study against CPET found 13.7% mean absolute error, but accuracy varies sharply by population: 23.8% overestimate in a healthy group, 102.4% in a Fontan-circulation group.

Apple deliberately renamed this to "Cardio Fitness" rather than using the technical term, and Fitbit uses the near-identical branded name "Cardio Fitness Score" for its own separate estimate, a genuine naming coincidence between two unrelated brands rather than a shared methodology. "Cardio Fitness" on an iPhone/Watch, "Cardio Fitness Score" on a Fitbit, and "VO2 Max" on a Garmin are all the same underlying concept, so someone comparing devices might not realize all three are estimating the same thing. Oura and Whoop don't offer a standalone VO2 max estimate of any kind.

Device measurement accuracy: Emerging · see the file
How each device actually shows this
Apple Watch "Cardio Fitness" (a branded name, not the scientific term) Garmin "VO2 Max" (keeps the scientific term directly) Fitbit "Cardio Fitness Score" RingConn "VO2 Max" Ultrahuman Ring "VO2 Max" Coros "Fitness Level" Polar Vantage "Polar Fitness Test" See every device →

Sources: Apple's own technical PDF, "Using Apple Watch to Estimate Cardio Fitness with VO2 max" (apple.com), a genuine primary source. Garmin's Firstbeat detail from Garmin's own technology page (garmin.com). Fitbit/Google's own support documentation (official); Freeberg KA et al., "Assessing the ability of the Fitbit Charge 2 to accurately predict VO2max," mHealth, 2019, doi:10.21037/mhealth.2019.09.07.

The benchmark
VO2 Max
VO2 Max by Age: What's Considered Good?

Where your number sits by age, and how far to trust your watch's estimate.

See how you compare
Example result
Man · 50 · 38
about the 69th percentile, Good for your age
ACSM data, 80,000+ adults
Research Desk · live file
See the full VO2 Max evidence file
Every claim rated Established, Emerging, Uncertain, Insufficient, or Unsupported, with a research log reviewed against new studies on a rolling basis.
Open the Research Desk
More on VO2 Max
What Is VO2 Max, and Why Does It Matter?
VO2 max measures how much oxygen your body can use during exercise. Here's what the research says about what it actually predicts for health.
How VO2 Max Is Actually Calculated
How is VO2 max calculated? I read the research on lab tests, field estimates, and wearable models to report what the evidence actually shows.
VO2 Max and Longevity: What the Evidence Actually Establishes
A look at what exercise-medicine research finds about cardiorespiratory fitness and all-cause mortality, and whether that link is just about body weight.
How Consumer Wearables Model VO2 Max From Heart Rate and Pace
Consumer wearables infer VO2 max from heart rate and pace, not breath analysis. Here is what the modeling actually involves and where it diverges from a lab test.
Can Medication Improve VO2 Max Without Exercise?
Can a medication raise VO2 max without exercise? A look at what a diabetes drug trial and exercise-snack research actually show about fitness gains.
Fitness vs Weight: What the Mortality Research Actually Shows
Research on fitness and weight finds cardio fitness predicts mortality risk more strongly than weight category in healthy adults, not in heart patients.
Do Short Bursts of Exercise Actually Raise Your VO2 Max?
Stair-climbing bursts and other brief bouts of exercise show up in trials as a real way to raise VO2 max. Here is what the randomized research actually found.
Do Fitness Trackers Actually Improve Health Outcomes?
Fitness trackers can shift how much you move, but does that translate into better health? Here's what the research on activity trackers and fitness actually establishes.
Does VO2 Max Protect Against Cognitive Decline?
Research links higher cardiorespiratory fitness to brain aging outcomes. Here's what the evidence actually establishes about VO2 max and cognitive decline.
HIIT vs Steady-State Cardio for VO2 Max
Does high-intensity interval training actually raise VO2 max faster than steady-state cardio? Here's what the controlled trials and meta-analyses found.
VO2 Max and Heart Failure Mortality: What the Evidence Actually Establishes
In heart failure, does VO2 max actually predict survival, or just correlate with it? Here's what the research on peak oxygen uptake and mortality shows.
Can a Proteomic Test Actually Predict VO2 Max?
A blood-based proteomic score has been linked to fitness and mortality risk in large cohorts. Here is what the research does and doesn't establish.
Zone 2 Training: Does the Popular VO2max Protocol Actually Hold Up?
Zone 2 training is marketed as the optimal way to build mitochondrial capacity. A 2025 narrative review argues the evidence behind that claim doesn't match the hype.
Does the Number of Sprints in a Sprint Interval Workout Actually Matter for VO2max?
Sprint interval training is sold on doing fewer, harder efforts. A 93-trial meta-analysis tested whether more sprints per session actually improves VO2max more.
Does Strength Training Improve VO2max as Much as Cardio?
A pooled analysis of 38 randomized trials in middle-aged and older adults compared aerobic training against resistance training head-to-head for VO2max.
Other metrics
Heart Rate VariabilityResting Heart RateSleepVO2 MaxWearable ECGCGMRecoveryActivityBlood Oxygen