Cardiorespiratory Fitness: What It Is and How to Measure Yours
Run these workouts on your iPhone, or hands-free on Apple Watch. Get PEAKVO2 Cardiorespiratory fitness is how well your heart, lungs, blood and muscles deliver and use oxygen during sustained exercise. The number that measures it is your VO2 max. It predicts death from any cause more strongly than smoking, high blood pressure or diabetes, and unlike those, almost nobody tracks it.
If a doctor or a study has used the phrase and you were not sure what it meant in practice, this covers it: what the term describes, what the number predicts, what counts as good for your age, and how to find yours without a laboratory.
What Is Cardiorespiratory Fitness?
It is the capacity of your body to take in oxygen, move it to working muscles, and use it to produce energy over a sustained effort. Four systems have to cooperate: lungs to take oxygen in, heart to pump it, blood to carry it, muscles to use it. Cardiorespiratory fitness is the measure of how well that chain works as a whole.
The number behind it is VO2 max, the maximum volume of oxygen you can use per minute, expressed per kilogram of body weight as ml/kg/min. That is the single most important thing to understand here: cardiorespiratory fitness and VO2 max are not two topics. One is the capacity, the other is its measurement.
The vocabulary splits by who is speaking. Researchers and clinicians say cardiorespiratory fitness. Watches, training apps and runners say VO2 max. If your doctor mentions the former, the number they mean is the one your watch may already be estimating.
The Health Marker Almost Nobody Tracks
Plenty of things genuinely matter for staying healthy, and most people already know the list: sleeping enough, eating reasonably, keeping blood pressure down, not smoking, keeping weight in a sane range, building strength, moving during the day. All of it is worth doing.
What is odd is which of these people measure. Blood pressure gets checked at every appointment. Cholesterol gets a blood test. Weight has a scale in most bathrooms. Steps are counted by a device most people carry anyway.
Cardiorespiratory fitness, which outperforms several of those as a predictor of mortality, is measured by almost nobody.
| Study | Population | Finding |
|---|---|---|
| Mandsager et al., 2018 | 122,007 patients | Elite fitness had an 80% lower mortality risk than the lowest group, with no upper limit to the benefit |
| Imboden et al., 2018 | 4,137 healthy adults, 24 years | Each 1 MET increase (about 3.5 ml/kg/min) associated with 11.6% lower all-cause mortality |
| Clausen et al., 2018 | 5,107 men, 46 years | Each unit increase associated with 45 additional days of life expectancy |
| Myers et al., 2002 | 6,213 men | Exercise capacity was a stronger predictor of death than smoking, hypertension or diabetes |
Read the Mandsager finding again, because it is the unusual one. For most health markers there is a target range, and past it more is not better. For cardiorespiratory fitness the researchers concluded there is no such ceiling: within the range they observed, fitter was always associated with lower mortality.
That combination, strongly predictive and almost never measured, is what makes it worth knowing your number.
What Counts as Good?
Like most physiological measures, it depends on your age and sex. The reference values come from the Cooper Institute cohort of more than 80,000 adults, as published in the ACSM exercise testing guidelines.
Roughly, the "good" band starts at:
| Age | Men | Women |
|---|---|---|
| 20s | 46 ml/kg/min | 37 ml/kg/min |
| 30s | 44 | 36 |
| 40s | 42 | 34 |
| 50s | 39 | 32 |
| 60s | 35 | 29 |
The full tables by decade, with every category from poor to superior, are in our VO2 max by age charts.
One thing worth saying plainly: the health benefit is steepest at the bottom. Moving from the poor category to average does more for your mortality risk than moving from good to excellent. If your number is low, that is the encouraging news, not the discouraging part.
How to Measure Yours
Four routes, in descending order of accuracy:
A laboratory test with gas exchange analysis is the gold standard. You run or cycle at increasing intensity wearing a mask that measures the oxygen you consume. It typically costs $100 to $250 and takes about 15 minutes. What to expect is covered in our VO2 max test guide, and you can find providers in our lab directory.
A wearable estimates it continuously. Apple Watch reports it as Cardio Fitness, Garmin and others simply as VO2 max. These estimates are accurate to within a few ml/kg/min for most people and are excellent for tracking your own trend, which matters more than the absolute value.
A field test gives you a number with nothing but a stopwatch:
- The Cooper test: run as far as you can in 12 minutes
- The beep test: progressive 20 metre shuttles
- The Rockport walk: one mile as fast as you can, plus your finishing heart rate
- The 1.5 mile run
A calculator turns any of those results into a number and a category. Ours is at VO2 max calculator, and all of these tests are also built into PEAKVO2 so the test, the number and the training sit in one place.
How to Improve It
It is highly trainable, and it responds at any age. People in their sixties have increased their cardiorespiratory fitness by 19 to 22 percent with structured training. Most people improve 5 to 15 percent in 8 to 12 weeks.
The formula is not complicated. Build the base with easy aerobic work in zone 2, then add one or two hard interval sessions per week. Four minute intervals at 90 to 95 percent of maximum heart rate, the Norwegian 4x4, raised VO2 max 7.2 percent in eight weeks in a controlled trial (Helgerud et al., 2007). The distribution that elite endurance athletes actually use is roughly 80 percent easy and 20 percent hard (Seiler, 2010), and most recreational exercisers invert it without noticing.
The training detail lives in how to improve your VO2 max and cardiovascular endurance.
Find your number, then move it
PEAKVO2 estimates your cardiorespiratory fitness from a built-in field test, shows your category for your age and sex, and runs the interval sessions that raise it, on iPhone and Apple Watch.
Get PEAKVO2 freeFrequently Asked Questions
What is cardiorespiratory fitness?
How well your heart, lungs, blood and muscles work together to deliver and use oxygen during sustained exercise. It is the clinical term for aerobic fitness, and the number that quantifies it is your VO2 max in ml/kg/min.
Is cardiorespiratory fitness the same as VO2 max?
Effectively yes. Cardiorespiratory fitness is the capacity, VO2 max is its measurement. Clinicians say one, wearables say the other, and they mean the same thing.
Why does cardiorespiratory fitness matter so much?
It predicts all-cause mortality better than most tracked risk factors. In 122,007 patients the fittest group had an 80 percent lower mortality risk than the least fit, with no upper limit to the benefit.
What is a good cardiorespiratory fitness level?
For men the good band starts near 46 ml/kg/min in the twenties, 42 in the forties and 35 in the sixties; for women roughly 37, 34 and 29. Moving up one category matters more than reaching elite values.
How do I measure my cardiorespiratory fitness?
A lab test is most accurate, a wearable estimates it continuously, and field tests such as the Cooper run, beep test or Rockport walk give you a number with a stopwatch. A calculator converts any result into a category.
Can you improve cardiorespiratory fitness at any age?
Yes. People in their sixties have improved 19 to 22 percent with structured training. Intervals near maximum heart rate on a base of easy aerobic work are the strongest stimulus.
How long does it take to improve?
Typically 5 to 15 percent in six to twelve weeks of consistent training. The earliest changes are circulatory and are felt before any test registers them.
References
- Mandsager K, Harb S, Cremer P, et al. Association of cardiorespiratory fitness with long-term mortality among adults undergoing exercise treadmill testing. JAMA Netw Open. 2018;1(6):e183605. PubMed
- Imboden MT, Harber MP, Whaley MH, et al. Cardiorespiratory fitness and mortality in healthy men and women. J Am Coll Cardiol. 2018;72(19):2283-2292. PubMed
- Clausen JSR, Marott JL, Holtermann A, et al. Midlife cardiorespiratory fitness and the long-term risk of mortality. J Am Coll Cardiol. 2018;72(9):987-995. PubMed
- Myers J, Prakash M, Froelicher V, et al. Exercise capacity and mortality among men referred for exercise testing. N Engl J Med. 2002;346(11):793-801. PubMed
- Helgerud J, Høydal K, Wang E, et al. Aerobic high-intensity intervals improve VO2max more than moderate training. Med Sci Sports Exerc. 2007;39(4):665-671. PubMed
- Seiler S. What is best practice for training intensity and duration distribution in endurance athletes? Int J Sports Physiol Perform. 2010;5(3):276-291. PubMed