Cardio fitness is your body’s ability to deliver and use oxygen during sustained physical activity. It is measured by VO2 Max, the maximum volume of oxygen you can consume per minute relative to your body weight (ml/kg/min). A higher cardio fitness level means your heart, lungs, and muscles work more efficiently together. It is one of the most important markers of overall health.
Cardio Fitness vs VO2 Max
They are the same thing expressed differently. Apple calls it “Cardio Fitness” in the Health app. The underlying measurement is VO2 Max. Fitbit calls it “Cardio Fitness Score.” Garmin just says “VO2 Max.” All refer to the same concept: your aerobic capacity, how much oxygen your body can use at peak effort.
The terminology varies by platform, but the science is identical. When your Apple Watch shows a cardio fitness level, it is estimating your VO2 Max using heart rate and motion data from outdoor workouts.
Why It Matters More Than You Think
VO2 Max is one of the strongest predictors of all-cause mortality. A 2018 Cleveland Clinic study of over 122,000 patients found that cardio fitness was more strongly associated with survival than nearly any other modifiable risk factor, including smoking status and blood pressure. The relationship was dose-dependent: higher fitness at any age was associated with longer lifespan, with no observed upper limit to the benefit.
The practical takeaway is straightforward. Improving your cardio fitness, even modestly, is one of the most impactful things you can do for your long-term health. Moving from the bottom 25% to the 25th-50th percentile carries a larger mortality reduction than many common medical interventions.
What the Levels Mean
| Level | VO2 Max Range | What It Means |
|---|---|---|
| Low | Below 20th percentile | Associated with higher health risks |
| Below Average | 20th-40th percentile | Room for meaningful improvement |
| Average | 40th-60th percentile | Typical for moderately active adults |
| Above Average | 60th-80th percentile | Good cardiovascular health |
| High | Above 80th percentile | Strong fitness, positive health outlook |
Specific VO2 Max numbers vary by age and sex. A “Good” score for a 30-year-old is different from a “Good” score for a 60-year-old. See the VO2 Max by age and gender chart for detailed ranges. Check your level with our Cardio Fitness Level Checker.
How to Check Yours
Apple Watch estimates your cardio fitness automatically after outdoor walks, runs, and hikes. You can find it in the Health app under Browse > Heart > Cardio Fitness. The reading updates as you accumulate more qualifying outdoor workouts.
Luen reads this estimate from Apple Health and shows you how it connects to your daily habits: exercise, sleep, daylight, and stress. Instead of a number sitting in the Health app, you get context, your percentile for your age group and the patterns that correlate with changes over time.
If your reading seems lower than expected, make sure you are doing enough outdoor workouts and that you are not measuring immediately after intense indoor exercise. The accuracy of the estimate depends on the quality and quantity of the data your watch collects. If your cardio fitness level dropped recently, see why your Apple Watch VO2 Max might have dropped.
Track your VO2 Max and Resting Heart Rate with Luen.
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Download for iOSFrequently Asked Questions
What does "cardio fitness" mean on Apple Watch?
Cardio fitness on Apple Watch is a measurement of your VO2 Max — the maximum amount of oxygen your body can use during exercise. Apple Watch estimates it during outdoor walks, runs, and hikes by analyzing your heart rate response relative to your pace. The Health app classifies your level as Low, Below Average, Above Average, or High based on your age and sex.
Why does my iPhone say my cardio fitness is low?
A "Low" cardio fitness notification means your VO2 Max estimate falls in the bottom 20th percentile for your age and sex. This could reflect your actual fitness level, or it could be caused by inaccurate Health profile data, walking after intense exercise, a recent watchOS update, or environmental conditions. Verify your Health profile and do consistent outdoor workouts before drawing conclusions.
How can I improve my cardio fitness level on Apple Watch?
The most effective approach is consistent aerobic exercise — aim for 150+ minutes per week of moderate activity like brisk walking, cycling, or swimming. Adding 1-2 interval sessions per week accelerates improvement. Most people see their cardio fitness level improve within 8-12 weeks of consistent training.