Cardiorespiratory fitness

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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.

Contents

In 2016, the American Heart Association published an official scientific statement advocating that CRF, quantifiable as V̇O2 max/peak, be categorized as a clinical vital sign and should be routinely assessed as part of clinical practice. [1] Low levels of CRF have been shown to increase the risk of cardiovascular disease (CVD) and all-cause mortality. [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. [1]

Regular physical activity and exercise can improve CRF, thus decreasing risk of CVD and other conditions while improving overall health. [3] [4]

History and etymology

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. [5] This measure was found to be dependent upon functional capacities of an individual's cardiovascular and respiratory systems. [5] He coined the term VO2 max, or maximal oxygen consumption, the numerical result of exercise testing that represents the maximum rate of oxygen consumed per kilogram of body mass per minute during exercise which now serves as the primary measure of CRF. This proposal ignited a multitude of studies demonstrating a relationship between VO2 max and cardiovascular disease and all-cause mortality.

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. [6]

The prefix "cardio-" refers to the heart while "-respiratory" links the heart and respiratory system, which includes organs that contribute to gas exchange in plants and animals, especially the lungs (animals). Fitness refers to an individual's state of health.

Exercise

Cardiorespiratory fitness can be increased by means of regular physical activity and exercise. 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. [3] [4] A 2005 Cochrane review demonstrated that physical activity interventions are effective for increasing CRF, [7] while other studies have determined that improved CRF is associated with lower risk of CVD and all-cause mortality. [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.), but studies show that high intensity interval training (HIIT) is highly effective in increasing CRF and VO2 max in people of all ages. [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. [11]

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. [14]

Various methods of measurement exist for determining an individual's cardiorespiratory fitness. VO2 max is the most commonly accepted indicator of CRF and has been since the 1960s. [15] Cardiopulmonary exercise testing (CPET) with spirometry is the gold standard for determining VO2 max. It requires the individual to perform exercise with analysis of gas exchange usually until maximal exertion is achieved. The use of electrocardiography is often used to examine heart response to exercise and exertion. [16] CPET is performed on a treadmill or a cycle ergometer. The method of test administration is based on the abilities of the test subject, as the cycle ergometer is generally less taxing on the body and often better suited for elderly populations, although is shown to sometimes produce results 10% - 20% lower in individuals not accustomed to cycling due to leg fatigue. [16]

In many cases, children or the elderly are not subjected to the vigor of cardiopulmonary exercise testing. There are other methods used to mathematically estimate the VO2 max of a test subject by having the subject walk or jog a certain distance in as little time as possible, complete the maximum number of repetitions of a short-distance run (commonly known as the PACER test in the United States), or walk on a treadmill at increasing incline until a sub-maximal goal is achieved, along with others. [17]

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. [18]

See also

Related Research Articles

<span class="mw-page-title-main">Exercise</span> Bodily activity intended to improve health

Exercise is intentional physical activity to enhance or maintain fitness and overall health.

<span class="mw-page-title-main">Heart rate</span> Speed of the heartbeat, measured in beats per minute

Heart rate is the frequency of the heartbeat measured by the number of contractions of the heart per minute. The heart rate can vary according to the body's physical needs, including the need to absorb oxygen and excrete carbon dioxide, but is also modulated by numerous factors, including genetics, physical fitness, stress or psychological status, diet, drugs, hormonal status, environment, and disease/illness as well as the interaction between and among these factors. It is usually equal or close to the pulse measured at any peripheral point.

<span class="mw-page-title-main">Aerobic exercise</span> Low to high intensity physical exercise

Aerobic exercise is physical exercise of low to high intensity that depends primarily on the aerobic energy-generating process. "Aerobic" is defined as "relating to, involving, or requiring oxygen", and refers to the use of oxygen to meet energy demands during exercise via aerobic metabolism adequately. Aerobic exercise is performed by repeating sequences of light-to-moderate intensity activities for extended periods of time. Examples of cardiovascular or aerobic exercise are medium- to long-distance running or jogging, swimming, cycling, stair climbing and walking.

<span class="mw-page-title-main">Exercise physiology</span>

Exercise physiology is the physiology of physical exercise. It is one of the allied health professions, and involves the study of the acute responses and chronic adaptations to exercise. Exercise physiologists are the highest qualified exercise professionals and utilise education, lifestyle intervention and specific forms of exercise to rehabilitate and manage acute and chronic injuries and conditions.

<span class="mw-page-title-main">Physical fitness</span> State of health and well-being

Physical fitness is a state of health and well-being and, more specifically, the ability to perform aspects of sports, occupations and daily activities. Physical fitness is generally achieved through proper nutrition, moderate-vigorous physical exercise, and sufficient rest along with a formal recovery plan.

<span class="mw-page-title-main">Cardiac stress test</span> Measures the hearts ability to respond to external stress in a controlled clinical environment

A cardiac stress test is a cardiological examination that evaluates the cardiovascular system's response to external stress within a controlled clinical setting. This stress response can be induced through physical exercise or intravenous pharmacological stimulation of heart rate.

V̇O2 max (also maximal oxygen consumption, maximal oxygen uptake or maximal aerobic capacity) is the maximum rate of oxygen consumption attainable during physical exertion. The name is derived from three abbreviations: "V̇" for volume (the dot over the V indicates "per unit of time" in Newton's notation), "O2" for oxygen, and "max" for maximum and usually normalized per kilogram of body mass. A similar measure is V̇O2 peak (peak oxygen consumption), which is the measurable value from a session of physical exercise, be it incremental or otherwise. It could match or underestimate the actual V̇O2 max. Confusion between the values in older and popular fitness literature is common. The capacity of the lung to exchange oxygen and carbon dioxide is constrained by the rate of blood oxygen transport to active tissue.

<span class="mw-page-title-main">Exercise intensity</span>

Exercise intensity refers to how much energy is expended when exercising. Perceived intensity varies with each person. It has been found that intensity has an effect on what fuel the body uses and what kind of adaptations the body makes after exercise. Intensity is the amount of physical power that the body uses when performing an activity. For example, exercise intensity defines how hard the body has to work to walk a mile in 20 minutes.

<span class="mw-page-title-main">High-intensity interval training</span> Exercise strategy

High-intensity interval training (HIIT) is a training protocol alternating short periods of intense or explosive anaerobic exercise with brief recovery periods until the point of exhaustion. HIIT involves exercises performed in repeated quick bursts at maximum or near maximal effort with periods of rest or low activity between bouts. The very high level of intensity, the interval duration, and number of bouts distinguish it from aerobic (cardiovascular) activity, because the body significantly recruits anaerobic energy systems. The method thereby relies on "the anaerobic energy releasing system almost maximally".

<span class="mw-page-title-main">Exercise intolerance</span> Medical condition

Exercise intolerance is a condition of inability or decreased ability to perform physical exercise at the normally expected level or duration for people of that age, size, sex, and muscle mass. It also includes experiences of unusually severe post-exercise pain, fatigue, nausea, vomiting or other negative effects. Exercise intolerance is not a disease or syndrome in and of itself, but can result from various disorders.

The multi-stage fitness test (MSFT), also known as the beep test, bleep test, PACER (Progressive Aerobic Cardiovascular Endurance Run), PACERtest, FitnessGram PACER test, or the 20 m Shuttle Run Test (20 m SRT), is a running test used to estimate an athlete's aerobic capacity (VO2 max).

The metabolic equivalent of task (MET) is the objective measure of the ratio of the rate at which a person expends energy, relative to the mass of that person, while performing some specific physical activity compared to a reference, currently set by convention at an absolute 3.5 mL of oxygen per kg per minute, which is the energy expended when sitting quietly by a reference individual, chosen to be roughly representative of the general population, and thereby suited to epidemiological surveys. A Compendium of Physical Activities is available online, which provides MET values for hundreds of activities.

Aerobic conditioning is a process whereby the heart and lungs are trained to pump blood more efficiently, allowing more oxygen to be delivered to muscles and organs. The skeletal muscles also become aerobically conditioned, as regular aerobic exercise produces a shift in muscle fibres from more type II into more type I (slow-twitch/oxidative). Type I muscle fibres have far more mitochondria than type II, making type I fibres the producers of adenosine triphosphate (ATP) primarily through oxidative phosphorylation rather than anaerobic glycolysis. Some neuromuscular diseases recommend regular aerobic exercise in order for the skeletal muscles to become aerobically conditioned, providing relief of symptoms or slowing the course of the disease, for example metabolic myopathies and Duchenne muscular dystrophy.

Interval training is a type of training exercise that involves a series of high-intensity workouts interspersed with rest or break periods. The high-intensity periods are typically at or close to anaerobic exercise, while the recovery periods involve activity of lower intensity. Varying the intensity of effort exercises the heart muscle, providing a cardiovascular workout, improving aerobic capacity and permitting the person to exercise for longer and/or at more intense levels.

Incremental exercise is physical exercise that increases in intensity over time.

<span class="mw-page-title-main">Bruce protocol</span> Test of physical fitness and cardiac health

The Bruce protocol is a standardized diagnostic test used in the evaluation of cardiac function and physical fitness, developed by American cardiologist Robert A. Bruce.

Preoperative rehabilitation, prehabilitation or prehab, is a form of healthcare intervention that takes place before a medical or surgical intervention with the aim to reduce side effects and complications, and enhance recovery. Multidisciplinary team involvement can range from physiotherapists, occupational therapists, respiratory therapists, doctors, pharmacologists, anesthesiologists, psychologists, psychiatrists and sports physiologists.

<span class="mw-page-title-main">Cardiovascular fitness</span> Heart-related component of physical fitness

Cardiovascular fitness refers to a health-related component of physical fitness that is brought about by sustained physical activity. A person's ability to deliver oxygen to the working muscles is affected by many physiological parameters, including heart rate, stroke volume, cardiac output, and maximal oxygen consumption.

In kinesiology, the ventilatory threshold (VT1) refers to the point during exercise at which ventilation starts to increase at a faster rate than VO2 (V – volume, O2 – oxygen). One's threshold is said to reflect levels of anaerobiosis and lactate accumulation. As the intensity level of the activity being performed increases, breathing becomes faster; more steadily first and then more rapid as the intensity increases. When breathing surpasses normal ventilation rate, one has reached ventilatory threshold. For most people this threshold lies at exercise intensities between 50% and 75% of VO2 max. A major factor affecting one's ventilatory threshold is their maximal ventilation (amount of air entering and exiting lungs). This is dependent on their personal experience with the activity and how physically fit the person is. Comparison studies of more athletic people have shown that your ventilatory threshold occurs at a higher intensity if you are more active or have been training for that exercise; although, in some cases shorter continuous tests can be used because of rapid alterations in ventilation.

The benefits of physical activity range widely. Most types of physical activity improve health and well-being.

References

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  2. 1 2 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): 2024–2035. doi:10.1001/jama.2009.681. ISSN   0098-7484. PMID   19454641.
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  6. ↑ 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.
  7. ↑ 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.
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  10. ↑ 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.
  11. 1 2 Wu, Zhi-Jian; Wang, Zhu-Ying; Gao, Hao-En; Zhou, Xian-Feng; Li, Fang-Hui (2021-07-15). "Impact of high-intensity interval training on cardiorespiratory fitness, body composition, physical fitness, and metabolic parameters in older adults: A meta-analysis of randomized controlled trials". Experimental Gerontology. 150: 111345. doi:10.1016/j.exger.2021.111345. ISSN   0531-5565. PMID   33836261. S2CID   233131437.
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  17. ↑ Buttar, Karampreet Kour; Kacker, Sudhanshu; Saboo, Neha (2022). "Normative Data of Maximal Oxygen Consumption (VO2 Max) among Healthy Young Adults: A Cross-sectional Study". Journal of Clinical and Diagnostic Research. doi: 10.7860/jcdr/2022/53660.16672 . ISSN   2249-782X. S2CID   251203633.
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