Cardiorespiratory fitness

Cardiorespiratory fitness (CRF) is the ability of the circulatory and respiratory systems to deliver oxygen to working muscles during sustained activity, most often quantified by VO2max. It integrates lung function, cardiac output, vascular health, and muscle oxidative capacity. Some large cohort studies (e.g., Mandsager et al. 2018) suggest low CRF can carry mortality risk comparable to or greater than smoking, hypertension, or diabetes, making CRF a powerful modifiable longevity predictor.