Cardiorespiratory fitness

Cardiorespiratory fitness (CRF) refers to the ability of the circulatory and respiratory systems to supply oxygen to skeletal muscles during sustained physical activity. Scientists and researchers use CRF to assess the functional capacity of the respiratory and cardiovascular systems. These functions include ventilation, perfusion, gas exchange, vasodilation, and delivery of oxygen to the body's tissues. As these body's functions are vital to an individual's health, CRF allows observers to quantify an individual's morbidity and mortality risk as a function of cardiorespiratory health.

See also: Cardiovascular fitness

An exercise stress test, either treadmill or cycling, entails using a graded-intensity aerobic stress to assess CRF for whether an individual can maintain physical exertion up to a heart rate of 85% of their age-predicted maximum.[1]

A 2005 Cochrane review demonstrated that physical activity interventions are effective for increasing CRF.[2] CRF may be associated with lowering the risk of cardiovascular diseases and all-cause mortality.[3][4][5][6]

History

The emergence of a method to quantify CRF began in 1923-1924. A.V. Hill et al. proposed a multifactorial relationship between the maximum rate of oxygen uptake by body tissues, termed VO2 max, and intensity of physical activity dependent upon and limited by functional capacities of an individual's cardiovascular and respiratory systems.[7] This proposal served as an impetus for a multitude of studies demonstrating a relationship between VO2 max and cardiovascular disease (CVD) and all-cause mortality. While many methods of estimating CRF exist, each has been validated as a vital tool for predicting morbidity and mortality risk.

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.[8]

Measurement

A method of estimating CRF entails using formulas, derived from extrapolated regressive analyses, to predict a theoretical level of CRF. These formulas take into consideration an individual's age, sex, BMI, substance use, relative levels of physical activity, and pathologic co-morbidites. 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.[9]

Cardiovascular system adaptations

The cardiovascular system responds to changing demands on the body by adjusting cardiac output, blood flow, and blood pressure. Cardiac output is defined as the product of heart rate and stroke volume which represents the volume of blood being pumped by the heart each minute. Cardiac output increases during physical activity due to an increase in both the heart rate and stroke volume.[10]

See also

References
  1. Lear, Scott A.; Brozic, Anka; Myers, Jonathan N.; Ignaszewski, Andrew (1999). "Exercise Stress Testing: An Overview of Current Guidelines". Sports Medicine. 27 (5): 285–312. doi:10.2165/00007256-199927050-00002. ISSN 0112-1642. PMID 10368877. S2CID 22350529.
  2. Hillsdon, M.; Foster, C.; Thorogood, M. (2005-01-25). "Interventions for promoting physical activity". The Cochrane Database of Systematic Reviews (1): CD003180. doi:10.1002/14651858.CD003180.pub2. ISSN 1469-493X. PMC 4164373. PMID 15674903.
  3. Myers, Jonathan; Prakash, Manish; Froelicher, Victor; Do, Dat; Partington, Sara; Atwood, J. Edwin (2002-03-14). "Exercise Capacity and Mortality among Men Referred for Exercise Testing". New England Journal of Medicine. 346 (11): 793–801. doi:10.1056/NEJMoa011858. ISSN 0028-4793.
  4. Blair, Steven N.; Brodney, Suzanne (1999-11-01). "Effects of physical inactivity and obesity on morbidity and mortality: current evidence and research issues:". Medicine & Science in Sports & Exercise. 31 (Supplement 1): S646. doi:10.1097/00005768-199911001-00025. ISSN 0195-9131.
  5. Kodama, Satoru (2009-05-20). "Cardiorespiratory Fitness as a Quantitative Predictor of All-Cause Mortality and Cardiovascular Events in Healthy Men and Women: A Meta-analysis". JAMA. 301 (19): 2024. doi:10.1001/jama.2009.681. ISSN 0098-7484.
  6. Cao, Chao; Yang, Lin; Cade, W. Todd; Racette, Susan B.; Park, Yikyung; Cao, Yin; Friedenreich, Christine M.; Hamer, Mark; Stamatakis, Emmanuel; Smith, Lee (2020-01-30). "Cardiorespiratory Fitness Is Associated with Early Death Among Healthy Young and Middle-aged Baby Boomers and Generation Xers". The American Journal of Medicine. 133 (8): 961–968.e3. doi:10.1016/j.amjmed.2019.12.041. ISSN 0002-9343. PMID 32006474.
  7. "Muscular exercise, lactic acid and the supply and utilisation of oxygen.— Parts VII–VIII". Proceedings of the Royal Society of London. Series B, Containing Papers of a Biological Character. 97 (682): 155–176. December 1924. doi:10.1098/rspb.1924.0048. ISSN 0950-1193.
  8. Ross, Robert; Blair, Steven N.; Arena, Ross; Church, Timothy S.; Després, Jean-Pierre; Franklin, Barry A.; Haskell, William L.; Kaminsky, Leonard A.; Levine, Benjamin D. (2016-12-13). "Importance of Assessing Cardiorespiratory Fitness in Clinical Practice: A Case for Fitness as a Clinical Vital Sign: A Scientific Statement From the American Heart Association". Circulation. 134 (24): e653–e699. doi:10.1161/CIR.0000000000000461. ISSN 0009-7322. PMID 27881567. S2CID 3372949.
  9. Nauman, Javaid; Nes, Bjarne M.; Lavie, Carl J.; Jackson, Andrew S.; Sui, Xuemei; Coombes, Jeff S.; Blair, Steven N.; Wisløff, Ulrik (2017-02-01). "Prediction of Cardiovascular Mortality by Estimated Cardiorespiratory Fitness Independent of Traditional Risk Factors: The HUNT Study". Mayo Clinic Proceedings. 92 (2): 218–227. doi:10.1016/j.mayocp.2016.10.007. ISSN 0025-6196. PMID 27866655. S2CID 3481095.
  10. Brown, S.P.; Eason, J.M.; Miller, W.C. (2006). Exercise Physiology: Basis of Human Movement in Health and Disease. Lippincott Williams & Wilkins. pp. 75–247. ISBN 978-0781777308.
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