Cardiorespiratory fitness (cardiorespiratory endurance) is the ability of the circulatory and respiratory systems to supply the working muscles with oxygen during prolonged physical exertion. Its main measure is VO2max, the maximal oxygen uptake.
It is one of the strongest markers of health and longevity: it is closely tied to the risk of death and underlies the estimation of fitness age.
What it is and how it is measured
Cardiorespiratory fitness reflects how efficiently the body takes up, transports and uses oxygen under sustained exertion. The gold standard of measurement is a cardiopulmonary exercise test with spirometry, where VO2max is determined in milliliters of oxygen per kilogram of body mass per minute (mL/kg/min). There are also simpler estimates — running and step tests, formulas based on age, sex and activity, and via load in METs.
Why it matters for longevity
Low cardiorespiratory fitness is associated with an increased risk of cardiovascular disease and premature death. By some estimates it is an even stronger predictor of mortality than smoking, hypertension, high cholesterol or diabetes. In 2016 the American Heart Association proposed regarding it as a clinical "vital sign." A 2023 meta-analysis showed that each additional MET of fitness is associated with about an 11% reduction in the risk of death, and the top third by VO2max with about 45% lower mortality compared with the bottom third.
Age and training
VO2max naturally declines with age: in men aged 20–29 it averages about 46 mL/kg/min, and by 80–89 years about 18. The good news is that cardiorespiratory fitness responds well to training at any age — regular aerobic exercise and interval training (HIIT) noticeably raise it. Heart-rate benchmarks for training help set the heart-rate zones and the maximum heart rate. Aerobic work is complemented by core stability — for example, the plank.
Calculate using this marker
Calculators where Cardiorespiratory fitness is used directly:
Frequently asked questions
Are cardiorespiratory fitness and VO2max the same thing?
VO2max is the main quantitative measure of cardiorespiratory fitness. Fitness itself is broader and includes the work of the heart, lungs, vessels and muscles.
Can cardiorespiratory fitness be improved after 50?
Yes. VO2max is trainable at any age: regular aerobic exercise and interval training raise it and lower health risks.