Cardiorespiratory Fitness

Cardiorespiratory Fitness (CRF)

• 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

• measurement of CRF following the initiation of an exercise training program can serve as motivation to the participant as reason for continuing with a regular exercise program and may encourage the addition of other modes of exercise to improve overall fitness

• CFR can assist in identifying, diagnosing, and prognosis of comorbid conditions

When considering/choosing an assessment

• the purpose of assessment 

• is physician supervision required 

• health status of participant 

• assessment intensity (max vs sub max) 

• duration of assessment 

• willingness of participant 

• cost of administration 

• required personnel 

• necessary equipment and facilities 

• potential safety concerns 

what is CRF?

• ability to perform large muscle, dynamic, mod-to-vig intensity exercise for prolonged periods of time 

• integrated physiologic and functional state of respiratory, cardiovascular, and musculoskeletal systems 

Concept of maximal oxygen uptake 

• criterion measure of CRF): maximal volume of oxygen consumed per unit of time (VO2max) 

  • expressed in relative (mL* kg*min) or absolute (mL * min) values

• VO2max: product of cardiac output (Q; L blood min) and arterial venous oxygen difference (A-VO2 diff; mL O2 L blood)

  • variation primarily from differences in Q *functional capacity of heart)

  • Q = HR x SV

• designation of VO2max means true physiologic limit has been reached

  • plateau of VO2 may be observed during final two work rates of a progressive exercise test

  • other criteria used to confirm VO2max:

    • plateau in HR (<2beats * min) or % of age-predicated max HR

    • respiratory exchange ratio (RER)

    • rating of perceived exertion (RPE)

    • post exercise blood lactate levels

  • no universal consensus

• peak VO2 (VO2peak) is often used if plateau does not occur, or performance is limited by muscular factors rather than central circulatory dynamics

  • common in populations with chronic diseases and health conditions

• open circuit spirometry (indirect calorimetry)

• absolute vs relative: net vs gross

• submaximal VO2 values acquired by direct measurements to predict VO2max using several equations

• sub-max exercise tests and field tests to measure/estimate VO2max 

• validated by: 

  • correlation between directly measured VO2max and estimated VO2max from physiologic responses to submaximal exercise 

  • correlation between directly measured VO2max and field test performance (time to run 1 or 1.5 mi) or time to volitional fatigue using a standard graded exercise test (GXT) protocol 

• potential for significant underestimation or overstimation of VO2max 

Max vs. Sub-max exercise testing 

• depends largely on the reasons for the rest, risk level of the individual, and availability of appropriate equipment and personnel

  • maximal tests require individuals to exercise to the point of volitional fatigue, which may be inappropriate for some individuals and may require the need for emergency equipment

• sub-max exercise tests

  • determine HR response to one or more submaximal work rates and use results to predict VO2max

  • various submaximal measures: HR, BP, workload, and RPE

• estimates of VO2max from HR response to submaximal exercise tests are based on the following assumptions:

  • a steady state HR is established for each work rate

  • a linear relatoinship exists between HR and work rate

  • the difference between predicated and actual MHR is small

  • mechanical efficiency (VO2 at a given rate) is the same for everyone

  • the individual is not on any HR altering medications

  • the individual is not using high quantities of caffeine, ill, or in a high temperature environment

CRF test sequence/measurements adn test termination criteria

• collect all necessary baseline measures (HR and BP) prior to initiating the test

• during the exercise test: HR, BP, and RPE should be collected

• RPE is valuable indicator for monitoring exercise tolerance

  • correlation between RPE and indicators of exercise intensity is strong, but interindividual variability of HR and blood lactate at specific RPEs is high

  • explanation of RPE scale is of utmost importance

  • used as indication of impending fatigue

HRmax = 220 - age

Modes of testing

• treadmill

• cycle-ergometer

• step

• sport specific

• field test

CRF: Maximal exercise Testing 

• greatest demand on the body

• the most challenging of all physical assessments for both the individual being assessed and the technician 

• these tests use increases in workload until peak exertion or exhaustion is achieved and serve three major purposes: 

  • diagnosis: most commonly used test to determine the presence of ischemic heart disease (ischemic threshold)

  • prognosis: determine the risk for an adverse event relative to disease history

  • evaluation: exercise response guides exercise prescription

Exercise testing and Risk of Cardiac Events

• the potential for an adverse event does exist based on the population being tested

• in a clinical setting, the risk of complications (death or an event requiring hospitalization) is usually considered to be approximately 1/10,000 or a range og 0-5/100,000 test

  • fatal events: 0.2-0.8-10,000 tests

  • non-fatal events: 1.4/10,000 tests

Maximal Treadmill Protocols for CRF

• Bruce: (3 min stages) most widely used T-mill protocol in US

  • predictive equations exist in active and sedentary men and women, patients with CVD, and older adults

• modified Bruce:

  • easier early stages then progress to standard Bruce: For high risk or older adults

• balke/ware (1 min stages)

  • constant speed 3.4 MPH with 1% grade increases/min. Equations exist in active and sedentary men and women.

• naughton: (2 min stage)

  • starts @ 1 mpg/0% grade —> 2 mph/0% grade —> each stage after increases by 2 mph/3.5% grade

• modified astrand: highly trained athletes

  • self selected speed with 5-min warm-up. (2 min stages) increases 2.5% grade every stage at selected speed to exhaustion.

• Kaminsky and Whaley: healthy sedentary individuals

  • incremental speed and grade increases with less gradual increases when compared to Bruce

Maximal cycle ergometry protocols 

• cycle ergometry testing utilizes a friction based or electronically braked ergometer

• work rate is usually expressed in kilogram-meters per minute (Kgm/min) and power output in watts (1 Watt = 6 kgm/min) 

• work rate = force x distance 

  • example: a monark bicycle ergometer has a belt that travels 6 meters/revolution. a person pedals againast 1 kg resistance at 50 RPm

  • work: 1 kg x (6 meters x 50 rpm) = 300 kgm/min

• power = force x distance/time

  • power: 300 kgm/min / 6 = 50 Watts

• Godfrey/James: 1 min stages, 60 RPM

  • based on size. everyone starts at 25 Watts

  • 10, 15, or 25 watt/min increases to exhaustion

• Astrand protocol: 2-3 min stages, 50 RPM

  • men: start at 600 kgm/min (100 Watts), increase by 50 watts/stage

  • women: start at 300 kgm/min (50 Watts), increased by 25 watts/stage

  • continue to exhaustion

• Storer-Davis protocol: 1 min stages, 60 RPM

  • warm-up 4-5 mins, 15 watts/min increase to exhaustion