<P> Cardiorespiratory fitness ( CRF ) refers to the ability of the circulatory and respiratory systems to supply oxygen to skeletal muscles during sustained physical activity . The primary measure of CRF is VO max . In 2016 , the American Heart Association published an official scientific statement advocating that CRF be categorized as a clinical vital sign and should be routinely assessed as part of clinical practice . </P>
a description of cardio-respiratory endurance as it relates to fitness
the ability of the circulatory and respiratory systems to supply oxygen to skeletal muscles during sustained physical activity