Cardiorespiratory fitness (CRF) refers to the ability of the circulatory and respiratory systems to supply oxygen to skeletal muscles during sustained physical activity.
[1][2] Some medical researchers claim that CRF is an even stronger predictor of mortality than smoking, hypertension, high cholesterol, type 2 diabetes mellitus, or other common risk factors.
[3][4] The emergence of a method to quantify CRF began in the 1920s when Archibald Hill, a British physiologist, proposed a multifactorial relationship between the maximum rate of oxygen uptake by body tissues and intensity of physical activity.
The medical community agrees that regular physical activity plays an important role in reducing risk of cardiovascular disease, stroke, hypertension, diabetes, and a variety of other morbid conditions.
[8][9][2][10] Multiple forms of exercise exist and are all generally beneficial to an individual's health (endurance running, weightlifting, sports activity, etc.
[11][12][13] A 2020 review of the literature by Wu et al. concluded that HIIT is effective in increasing CRF, physical fitness, muscle power, cardiac contractile function, and reducing blood triglycerides in older individuals.
In 2016, Nauman and Nes et al. demonstrated the added and unique utility of estimated cardiorespiratory fitness (eCRF) in predicting risk of cardiovascular disease and all-cause mortality.