Cardiorespiratory fitness tests measure aerobic fitness during moderate-to-high-intensity exercise. Aerobic fitness is the capacity of the heart, lungs, and blood to deliver oxygen to large working muscle groups, and the utilization of oxygen by those muscles.
Because cardiorespiratory fitness depends on combined functioning of the cardiovascular, respiratory, and skeletal muscle systems, cardiorespiratory fitness tests are good indicators of overall health. Poor performances on fitness tests are associated with premature deaths from all causes, especially cardiovascular disease. Over time, regular moderate-intensity exercise can improve cardiorespiratory fitness and lower risk factors. Thus, cardiorespiratory fitness tests can be strong motivators for increasing physical activity. One study found that 63% of subjects made healthy lifestyle changes after being tested.
In addition to assessing current aerobic capacity, cardiorespiratory fitness tests are used to select appropriate physical activities, identify specific training requirements, and design individualized exercise programs. The tests can be used to monitor progress and evaluate the effectiveness of specific fitness regimens.
Cardiorespiratory fitness tests can help identify physical limitations. They can monitor heart rate (HR) and blood pressure responses to exercise and help identify potentially dangerous cardiovascular responses. A special type of cardiorespiratory fitness test, known as a stress test, is used in the diagnosis of cardiovascular disease.
The major types of cardiorespiratory fitness tests are walk/run tests, step tests, cycle ergometer tests. There are many different protocols for each type of test. Test choice depends on a variety of factors, including presumed physical fitness, available equipment and facilities, preferred activity, and any musculoskeletal limitations or balance problems. Swimming and wheelchair protocols are available.
Most tests require an accurate body weight determination before the test and either an electronic HR monitor or an HR check at or near the end of the test. HR can be determined by taking one's radial pulse on the inside of the wrist at the base of the thumb. To obtain an HR in beats per minute (bpm), the pulse is counted for 10 seconds and multiplied by 6 or counted for 15 seconds and multiplied by 4. HR can also be measured with a stethoscope.
Cardiorespiratory fitness tests can be either maximal or submaximal. Younger, healthy subjects who want an estimate of their cardiorespiratory fitness are more likely to perform a maximal test. Submaximal tests usually aim for just above 75% of the participant's predicted maximum HR. Fitness centers and personal trainers generally perform submaximal tests because they lack emergency personnel and facilities to deal with unexpected adverse responses.
Walk/run tests are the most common tests because they are easy to conduct and appropriate for people of all ages and fitness levels. Walk tests are more appropriate for adults who are unaccustomed to physical activity or are unable to run. Since walk tests are submaximal and lower impact, there is less risk of adverse events. However, walk tests should raise the HR above 120 bpm. Although 1-mile (1.6-km) or 1.5mile (2.4-km) walk/runs are most common, the distance can be shortened to 600 yards (549 m) or one-quarter mile (402 m) for older adults.
The objective of most walk/run tests is to cover the distance as fast as possible with pacing and without overexertion. Time is recorded in minutes and seconds. Thirty seconds are subtracted for walk/run tests performed at altitudes of 5,000 feet (1,524 m), with another 10 seconds subtracted for each additional 1,000 feet (305 m) in altitude. With some protocols, the subject runs as fast as possible for 12 minutes and the distance covered is recorded.
Walk/run tests can be performed either on a treadmill or in the field. Treadmills can be carefully controlled for speed and grade. Field tests require an indoor or outdoor track, which are common in schools and parks, or a level road or path with marked distances. One mile (1.6 km) is four laps around the innermost lane of a standard quarter-mile (402-m) track, and 1.5 miles (2.4 km) is six laps.
Among the more common walk/run protocols:
There are various three- and five-minute step-test protocols. The original five-minute step test was developed during World War II at the Harvard University Fatigue Laboratory. A common three-minute test uses a step, bench, or bleacher that is 16.25 in. (41.28 cm) high. The test is performed to the beat of a metronome—two beats up and two down—at 96 bpm (24 steps per minute) for males and 88 bpm (22 steps per minute) for females.
Cycle ergometer tests can measure HR and blood pressure during exercise since upper-body movement is minimized. While cycling is a nonweight-bearing exercise, it is less stressful for the lower body and may be more appropriate for people who are obese or have orthopedic limitations. However, a cycle ergometer may be more difficult for people who are not used to cycling.
Cycle ergometer protocols are generally more complicated than treadmill tests. The workload on the cycle is set according to various factors, including age, gender, and perceived physical fitness. The Astrand-Rhyming protocol is a single-stage test that aims for a steady HR over six minutes, with the workload set during the first minute. The YMCA multistage protocol progressively increases the workload based on HR response. With some protocols, the cyclist continues at 50 rpm until the HR reaches about 75%–85% of maximum.
People with health problems or risk factors should consult a physician before undergoing cardiorespiratory fitness testing. The American College of Sports Medicine defines testing risk categories as:
Walk/run field tests that require covering a specified distance in a specified time or in the shortest possible time may require near-maximum or all-out effort by some people. These tests may not be appropriate for sedentary individuals who are at increased risk for cardiovascular disease or musculoskeletal conditions. Participants should stop immediately if they feel dizzy, nauseous, or lightheaded. The President's Challenge warns that the one-mile walk should not be attempted by anyone who does not routinely walk at least 15–20 minutes several times weekly. The 1.5-mile run should not be attempted by anyone who does not run continuously for at least 20 minutes at least 3 times per week.
Preparation for cardiorespiratory fitness testing includes a health screening to identify any medical contraindications, the need for medical supervision, other special requirements, and risk factors or symptoms that require medical evaluation or an exercise stress test. The test type and protocol should be selected according to the participant's health history and physical activity level.
Participants should wear comfortable, loose-fitting exercise clothing and appropriate shoes. They should be well-hydrated, have had a good night's sleep, and have abstained from alcohol for 24 hours prior to the test. They should abstain from food, caffeinated drinks, and tobacco for two to three hours before testing. They should not have engaged in exercise or strenuous activity on the test day.
Height, weight, resting blood pressure and HR, and 75% of maximum HR are usually determined before testing. Maximum HR is age in years subtracted from 220 bpm. For choosing the appropriate protocol, aerobic capacity can be estimated by dividing the maximum HR by the resting HR and multiplying by 15.
Test procedures should be explained carefully and testing should be performed at a comfortable temperature. Pacing is very important for maximizing scores and poor pacing is a major source of error in the tests. A trial test can be taken one week before or the subject can practice walking, running, or cycling at the correct pace for a short distance during the warm-up. Before a step test, participants should practice stepping to the metronome beat. The cycle ergometer seat height must be adjusted to a comfortable pedaling position, with the knee almost straight (5°) at the bottom of the stroke with the ankle in neutral position. If the seat is too low, test results may not be accurate.
Walking or jogging slowly for about five minutes is an appropriate cool down following a cardiorespiratory fitness test.
When proper precautions and appropriate protocols are followed, cardiorespiratory fitness tests are usually safe and fairly accurate. Subjects who are at risk for medical complications should only be tested under medical supervision.
Most cardiorespiratory fitness tests are designed to estimate or determine VO2 max. This is the maximum volume of oxygen (O2) in milliliters (mL) consumed per kilogram (kg) of body weight per minute (mL/kg/min). VO2 max is the aerobic capacity—how much oxygen can be transported by the heart, lungs, and blood to the muscles and utilized by the muscles during exercise. It is the point at which no more oxygen can be consumed, even if the workload is increased.
VO2 max is primarily determined by cardiac output—the maximum amount of blood pumped by the heart per minute—and by the amount of oxygen utilized by exercising muscles, which is the difference in oxygen content between the arterial and venous blood. Cardiac output depends primarily on the heart's contractile ability and on the size of the left ventricle. VO2 max also depends on lung strength and capacity and on body weight.
There are various ways to calculate VO2 max. Different tests and protocols and different calculation methods require different information. The calculation generally requires gender, age in years, body weight, HR, and the testing time or distance covered. Various online calculators are available for VO2 max and percentile rankings. For example, a 50-year-old woman with a VO2 max in the 50th percentile scored higher than 50% of women aged 50–59 who took the same test. Some calculators include the energy cost of the exercise or metabolic equivalent of task (MET).
Various factors can affect the accuracy of the calculated VO2 max. Some tests can only accurately measure cardiorespiratory fitness in people within a specific age range. With submaximal testing, VO2 max is estimated from the HR response. Therefore it is dependent on having achieved a steady-state HR at each workload, as well as accurate HR measurements. Various factors—such as stress, anxiety, caffeine, or isometric muscle work—can affect the HR.
Field tests can have a VO2 max error rate as high as 10%–20% since they depend on pacing ability and motivation. Accuracy can also be affected by failure to maintain steady walking or running mechanics on a treadmill or constant speed on a cycle. Cycle ergometer tests are self-paced and not as carefully controlled as treadmill tests. Leg muscles may become prematurely fatigued, so that higher submaximal or true maximum output is not achieved, leading to a 10%–15% underestimate of aerobic fitness. Because of the longer muscle contractions on a cycle compared with a treadmill, blood pressure readings may be somewhat increased.
The results of cardiorespiratory fitness tests often motivate people to improve their fitness. Even those with a very low VO2 max (less than 28) can reach a normal range of 35–40 with just two to three 30–40-minute sessions of cardiovascular training every week, regardless of age.
See also Cardiovascular system ; Metabolic equivalent of task .
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YMCA of the USA, 101 N. Wacker Dr., Chicago, IL, 60606, (800) 872-9622, http://www.ymca.net .
Margaret Alic, PhD