Why Cardiorespiratory Fitness May Be the Best Predictor of a Long Life

Cardiorespiratory fitness is the body's ability to deliver and use oxygen during sustained exercise: essentially, how well the heart, lungs, and muscles work together. It is usually measured on a treadmill or bike test, but most people experience it as how winded they get climbing stairs or keeping up on a brisk walk. It turns out to be one of the most powerful predictors of long-term health available.

This guide covers what the research shows about fitness and longevity, and the simple ways to build it.

The essentials at a glance

• In a study of over 122,000 adults, those with low fitness had about 5 times the risk of death of the most fit, a gap as large as or larger than smoking, diabetes, or coronary artery disease (Mandsager et al., 2018).
• There was no upper limit to the benefit: being extremely fit was associated with the lowest risk of all.
• Unlike age or genetics, fitness is trainable: it improves with regular aerobic and interval exercise.

What the research found

In 2018, researchers analysed more than 122,000 adults who had completed a treadmill fitness test at a major clinic and tracked who died over the following years. The least-fit group had roughly five times the risk of death of the elite-fitness group. Strikingly, low fitness was as strong a risk factor as (or stronger than) smoking, diabetes, and existing heart disease. And the benefit kept climbing with fitness: there was no point at which being fitter stopped helping.

This is observational data, so it shows a powerful association rather than absolute proof of cause. But the size and consistency of the effect, plus the fact that fitness improves with training, make it one of the most actionable findings in preventive health.

How to build cardiorespiratory fitness

Fitness responds to regular aerobic training. Meeting the standard activity guidelines (150–300 minutes a week of moderate activity, or 75–150 minutes of vigorous) is a strong foundation. Adding some higher-intensity intervals (short bouts of hard effort, with recovery between) is an efficient way to raise cardiorespiratory fitness specifically. For someone starting from a low base, the good news is that the largest relative gains come from the first steps out of inactivity, so any consistent increase pays off.

Frequently asked questions

Is fitness really a bigger risk factor than smoking?

In the 2018 Cleveland Clinic analysis, low cardiorespiratory fitness was associated with a mortality risk as large as or larger than smoking, diabetes, or coronary artery disease. It's observational, but the effect is striking and consistent.

Can I improve my cardiorespiratory fitness?

Yes, it is one of the most trainable health markers. Regular aerobic exercise plus occasional higher-intensity intervals raises it, and the biggest relative gains come when an inactive person starts moving.

References

1. 1Association of Cardiorespiratory Fitness With Long-term Mortality Among Adults Undergoing Exercise Treadmill Testing (Mandsager et al.) · JAMA Network Open, 2018. Accessed 2026-05-26.
2. 2WHO Guidelines on Physical Activity and Sedentary Behaviour (2020) · World Health Organization. Accessed 2026-05-26.
3. 3World Health Organization 2020 guidelines on physical activity and sedentary behaviour (Bull et al.) · British Journal of Sports Medicine, 2020. Accessed 2026-06-08.
4. 4Cardiorespiratory fitness is a strong and consistent predictor of morbidity and mortality among adults: an overview of meta-analyses representing over 20.9 million observations from 199 unique cohort studies (Lang et al.) · British Journal of Sports Medicine, 2024. Accessed 2026-06-08.