![]() O 2max is the product of the maximal cardiac output ( L blood ∙ min −1) and arterial–venous oxygen (a- O 2) difference (mL O 2 ∙ L blood −1) or put more simply, delivery ( ) and utilization (a- O 2 difference) and is illustrated in the following equation (Fick equation):ĭifferences in O 2max across populations and fitness levels result primarily from differences in therefore, O 2max is closely related to the functional capacity of the heart (delivery). Both net and gross O 2 can be expressed in either absolute (L ∙ min −1) or relative terms (mL ∙ kg −1 ∙ min −1). Net O 2, on the other hand, represents the rate of oxygen consumption in excess of an individual’s resting O 2 and is used to describe the caloric cost of exercise. Gross O 2 represents the total rate oxygen consumed (or caloric cost) at rest and during a bout of exercise. The rate of oxygen consumption can also be expressed as gross O 2 or net O 2. It has been proposed that expressing O 2max relative to an individual’s fat-free mass (mL ∙ kg FFM −1 ∙ min −1) would provide a more accurate estimate of his or her CRF and is independent of changes in body mass ( 19). Maximal Oxygen Consumption: Net and Gross Rates When expressing O 2max simply as a linear function of body mass, CRF may be underestimated for heavier individuals (>75.4 kg) and overestimated for lighter individuals (<67.7 kg) ( 32). Relative O 2 is often used to estimate energy expenditure of weight-bearing activities such as walking, running, and stair climbing. O 2max is most often described relative to an individual’s body weight thus, relative O 2max is expressed in milliliters per kilogram of body weight per minute (mL ∙ kg −1 ∙ min −1) and is used to classify an individual’s CRF level to allow for meaningful comparisons between/among individuals with differing body weight. Absolute O 2max is directly related to body mass or size and is typically greater in men compared with women. Absolute O 2max is expressed in liters per minute (L ∙ min −1) or milliliters per minute (mL ∙ min −1) and provides a measure of energy expenditure for both non–weight- and weight-bearing activities such as arm or leg cycle ergometry and the treadmill. This variable is typically expressed in absolute or relative terms. Maximal volume of oxygen consumed per unit of time ( O 2max) is accepted as the criterion measure of CRF. Maximal Oxygen Uptake (Absolute and Relative) What equipment and facilities are needed for the test? What personnel are needed ( i.e., qualifications)? Whether physician supervision is required What will the information be used for (functional capacity, ExR x)? The following are some of the factors to consider when choosing the appropriate type of test: It is important to choose the test that best fits the patient’s characteristics. Last, the assessment of CRF can assist in identifying, diagnosing, and prognosis of comorbid conditions. Additionally, the measurement of CRF following the initiation of an exercise training program can serve as motivation to the patient as reason for continuing with a regular exercise program and may encourage the addition of other modes of exercise to improve overall fitness. Measurement (or assessment) of CRF can assist the professional by providing valuable information that can be used to determine the intensity, duration, and mode of exercise recommended as part of an exercise program. Measuring Cardiorespiratory Fitness and the Maximal Oxygen Uptake ![]() The skills and knowledge required to complete the assessment, interpret the results, and write an appropriate exercise prescription (ExR x) are an important responsibility of the exercise professional. The assessment of CRF is, therefore, an important part of any primary or secondary prevention and rehabilitative program. Increases in CRF result in a reduction in all-cause mortality ( 12, 13, 38, 61, 64). Low levels of CRF are associated with a marked increase in all-cause mortality (specifically from cardiovascular disease ). This type of association can be characterized as a dose-response relationship. Higher levels of CRF are often associated with higher levels of physical activity, which are associated with a number of health benefits. ![]() Thus, the ability to sustain this level of exertion is dependent on the integration of the respiratory, cardiovascular, and musculoskeletal systems. It is characterized by the body’s ability to perform moderate- to vigorous-intensity exercise using large muscle groups in a dynamic/rhythmic and continuous manner for prolonged periods of time. For additional ancillary materials related to this chapter, please visit thePoint.Ĭardiorespiratory fitness (CRF) is one of the five health-related components of physical fitness (CRF, body composition, muscular strength, muscular endurance, flexibility). ![]()
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