Cardiorespiratory fitness describes how well the heart, lungs, blood and muscles work together during sustained exercise. A 2024 overview identified 26 systematic reviews with meta-analysis, representing more than 20.9 million observations from 199 unique adult cohort studies.
Across included meta-analyses, each one-MET higher level of fitness was associated with an 11%–17% lower rate of all-cause mortality. One MET equals 3.5 mL of oxygen per kilogram per minute.
Why the number needs restraint
The underlying evidence is prospective cohort research. Higher fitness precedes lower disease and mortality rates, and the association is consistent, but participants were not randomized to remain more or less fit for years. Genetics, disease, activity, smoking and socioeconomic factors may influence both fitness and outcomes.
Measured is not the same as estimated
A separate 2024 systematic review and meta-analysis covered 42 studies, 35 cohorts and 3.8 million observations. Directly measured, exercise-estimated and non-exercise-estimated fitness all predicted mortality, but they are not interchangeable. A watch-generated VO₂ max is an estimate, not a laboratory cardiopulmonary exercise test.
Practical implication
Improving aerobic capacity is a defensible training goal, especially from a low baseline. Regular walking, running, cycling, rowing and other sustained activities can contribute, with intensity and progression matched to experience. The population evidence cannot select an individual program, clear symptoms or replace clinical exercise testing when that is indicated.
References
- Lang JJ et al. Cardiorespiratory fitness and morbidity/mortality: overview of meta-analyses. PubMed 38599681; DOI.
- Ross R et al. Importance of assessing cardiorespiratory fitness in clinical practice: AHA scientific statement. PubMed 27881567.
- Comparison of objectively measured and estimated fitness for mortality prediction: systematic review and meta-analysis. PubMed 39271056.