Surrogate Markers of Cardiorespiratory Fitness for Performance and Health: A Narrative Review

Cardiorespiratory fitness (CRF) is both an indicator of athletic performance and disease and mortality risk. The gold standard for measuring CRF is a VO2peak test, which is inaccessible to the general population and non-elite athletes. Thus, there is a need to identify surrogate markers for CRF that can easily be implemented in the general population and in athletes. This narrative review aims to identify easily measured surrogate markers of CRF that correlate with CRF and changes in CRF, predict or correlate with athletic performance, and correlate with health outcomes and changes in health outcomes. Time to fatigue was identified as the most complete surrogate marker of CRF in both the general population and in athletes. However, other surrogate markers of CRF, such as time trials, may also be implemented if time to fatigue is not suitable.