Cardiorespiratory Fitness (CRF) | August 2023 | Clinical Corner

August 1, 2023


Cardiorespiratory Fitness (CRF)


Even small changes in cardiorespiratory fitness (CRF) have a considerable impact on clinical symptoms and mortality risk among individuals with or without cardiovascular disease, as observed in United States veterans study analyzed from over 93,000 U.S. veterans. The mortality risk was greatly attenuated in those who were moderate and high fit at baseline who displayed declining fitness over time. CRF is not a short-lived benefit but carries a certain protection over time. Also, the level of exercise necessary to positively impact mortality risk is relatively small. Study was published online in the Journal of American College of Cardiology March 20, 2023.

One MET is defined as the energy you use when you are resting or sitting still. An activity that has a value of 4 METs means you are exerting four times the energy than you would if you were sitting still. Changes in CRF of 1.0 MET (metabolic equivalents) were inversely and proportionately related to mortality regardless of the baseline CRF status. For instance, a decline of 2.0 MET was associated with a 74% increased mortality risk for low-fit individuals with CVD and a 69% increase for those without CVD.

The findings suggest that CRF is a significant contributing factor in mortality and providers need to constantly encourage increased physical activity especially in middle-aged and older individuals regardless of any comorbid conditions. CRF appears to be an independent determinant of all-cause mortality regardless of genetic factors or underlying comorbid conditions. It appears that CRF is underestimated as an index of health outcomes and survival. Moderate to vigorous physical activity should be regularly promoted by the medical community but any level of increased activity should be beneficial.

Other benefits of exercise that clinicians may not be aware of:

-Each one-MET increase and CRF is associated with approximately 16% reduction in mortality.

-At any given risk factor profile for coronary calcium score, unfit persons have 2-3 times the mortality as their fit counterparts.

-Fitness is inversely related to annual health care costs (each 1-MET increase in CRF is associated with 6% lower annual health care costs).

-Physically active individuals hospitalized with acute coronary syndromes have better short-term outcomes which appear to be related to exercise preconditioning.

-Fit people who undergo elective or emergent surgical procedures have better outcomes.

-Regular physical activity is a common characteristic in population subsets who live into their 90s and 100s.

We, as physicians and medical providers, need to continue promoting the value of regular exercise at any level and to all our patients.


  1. Journal of American College of Cardiology (2023 Mar 20. Doi:10.1016/j.jacc.2023.01.027).
  2. Family Practice News Vol.53 No.4 April 2023

A special thanks  to Dr. Henry Szelag, Family Physician at McLaren Central Michigan, for submitting this clinical corner.