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On the Web - Concept 07

Web07-01: Cardiovascular Fitness Relationships

Web07-02: Measurement and Interpretation of Maximal Oxygen Consumption

Web07-03: Health Risks Associated with Low Fitness

Web 7-04: Fitness provides protection against health risks of obesity

Web07-05: Development of Field Tests of Aerobic Fitness

Web07-06: Cardiovascular Fitness Assessments

Web07-07: Supplemental Web Resources

Web07-08: Supplemental Readings

Web07-01: Cardiovascular Fitness Relationships

An understanding of the bodies' adaptations to aerobic exercise requires a basic knowledge of some exercise physiology relationships. There are two key formulas that are used to describe the cardiovascular responses to exercise:

Cardiac output (Q) is a parameter that refers to the amount of blood pumped by the heart per minute. The formula for cardiac output is shown in equation 1. Cardiac output equals the product of heart rate (# of beats per minute) and the stroke volume (amout of blood pumped per beat). During exercise both values increase to increase cardiac output and provide more oxygenated blood to the working muscles. In equation #1, cardiac output is represented as the product of heart rate (# of beats per minute) and the stroke volume (amout of blood pumped per beat).

The amount of oxygen taken up and used by the body is referred to as VO2. The equation for VO2 equals the cardiac output times a parameter known as the arterial-venous difference (av O2). The av O2 reflects the amount of O2 taken up by the tissues while the blood is circulating the body. A higher avO2 implies that more oxygen is taken up from the blood. During exercise, the avO2 difference increases to allow the body to take up more oxygen from the blood.

The higher cardiac output and higher avO2 difference causes the VO2 values to be higher during exercise. This allows the body to produce as much energy as possible through the aerobic metabolic pathways. The chart below shows how some of the cardiovascular parameters change from rest to exercise.

Web07-02: Measurement and Interpretation of Maximal Oxygen Consumption

Maximum oxygen consumption (VO2 max ) is the best indicator of cardiovascular fitness. In a laboratory setting, VO2 max can be directly measured by collecting and analyzing the gases (O2 and CO2) that a person exhales during a bout of maximal exercise. Because the concentration of oxygen (O2) in room air is known, the difference between room air and exhaled air is the amount of O2 that was consumed. Elite endurance athletes have highly conditioned cardiovascular systems (See Web08-01) and can take in and consume large amounts of oxygen during exercise.

The figure shows a typical laboratory setup for a VO₂ max test. The mouthpiece allows the participant to breath in room air but, due to a one-way valve, all of the exhaled air goes into the metabolic cart through the attached hoses. While any form of exercise could theoretically be used, treadmill running is by far the most common one. A main reason for this is that is possible to progressively increase the speed and grade of the treadmill until the participant can no longer maintain the pace or reaches volitional fatigue.

Some sample VO₂ max values are presented below to provide a general measure for comparison. These are not absolute standards but rather rough estimates of the typical values for different populations. Frail elderly may have max values as low as 10-15 ml/kg/min (or about 3-4 METS). Elite athletes, on the other hand, may have max values as high as 70 ml/kg/min (20+ METS).

Typical VO₂ max values in ml/kg/min

While the slide shows differences between males and females in terms of relative aerobic fitness, these differences are not apparent when differences in levels of body fatness are taken into account. Males have higher aerobic fitness on a pound for pound basis because they typically have lower levels of body fat (which has a low oxygen requirement). Therefore, direct comparisons between males and females are best made when the data are expressed as ml/kg of lean body weight.

Web07-03: Health Risks Associated with Low Fitness

A number of studies have examined links between physical activity/physical fitness and health. One of the more valuable databases is from The Aerobic Center Longitudinal Study (ACLS), an ongoing epidemiological study of patients that come through the Cooper Clinic (Dallas, TX) for preventive medical screens. This cohort study has followed over 20,000 people for over 30 years and examined the relationship between various lifestyle factors and health outcomes. Aerobic capacity in this study is assessed by a treadmill VO₂ max test. Percentile based norms are used to categorize participants into different fitness categories. Studies have conclusively demonstrated that individuals in the bottom 20% of the fitness distribution have greater risks of cardiovascular disease and all-cause mortality than individuals with moderate (20^th -60^th percentile) or high levels of fitness (60^th to 100^th percentile). These effects are independent of body fat level or other cardiovascular risk factors. Studies from this database have demonstrated that being unfit is a risk that adds to the risks already associated with other established risk factors.

To provide guidelines on the amount of activity required to obtain healthy fitness levels, researchers at the Cooper Institute analyzed the activity patterns of the participants in the same ACLS database. They found that an average leisure time physical activity level of 7-22 kcal/kg/week for men or 7-21 kcal/kg/week for women were associated with a moderate to high level of cardiorespiratory fitness. This amounts to approximately 525-1650 calories a week for males and approximately 420-1260 calories a week for females. See the graphic below. Considering that walking expends approximately 100 calories per mile, it does not require large amounts of activity to obtain significant health benefits.

Reference: Stofan, J.R., DiPietro, L., Davis, D., Kohl, H.W. III, and Blair, S.N. (1998). Physical activity patterns associated with cardiorespiratory fitness and reduced mortality: The Aerobics Center Longitudinal Study. American Journal of Public Health., 88: 1807-1813.

The concept of "metabolic fitness" has gained considerable attention in recent years as the links between physical activity and various metabolic factors become more established. Syndrome X is a metabolic syndrome characterized by the presence of insulin resistance, hyperinsulinemia, dyslipidemia, essential hypertension, glucose intolerance and an increased risk of non-insulin diabetes mellitus and cardiovascular disease.

Studies have revealed strong relationships found between aerobic fitness and the various indicators of metabolic syndrome. For example, one study from the Aerobic Center Longitudinal Study at the Cooper Institute compared the levels of different metabolic variables in fit and unfit individuals. For both men and women, the levels of the four metabolic variables comprising the "deadly quartet" (Kaplan et al., 1989) are lower for individuals with higher levels of fitness. This indicates that aerobic fitness can lead to improvements in metabolic fitness. See chart below.

Chart adapted from the following reference:
Whaley, M.H., Kampert, J.B., Kohl, H.W., & Blair, S.N. (1999). Physical fitness and clustering of risk factors associated with the metabolic syndrome.

Web 7-04: Fitness provides protection against health risks of obesity

The general assumption in our society is that an overweight or obese person is probably physically inactive and unfit. People also assume that a thin individual is probably physically active, physically fit and healthy. Research on this topic has determined that these generalizations are not accurate. It is clearly possible for overweight individuals to maintain high levels of fitness. Through participation in regular physical activity, it is also possible for overweight individuals to have good health and low risks for chronic disease.

Much of this evidence came from some epidemiological studies conducted at the Cooper Institute for Aerobics Research. In one study (Lee, 1999), the researchers studied a population of 21,925 men aged 30-83 who had completed a maximal treadmill tests and body composition assessment as part of a preventive medical visit to the Cooper Clinic. The population was divided by body composition levels into Lean (< 16.7% fat), Normal (16.7-25%) and Obese (> 25) and then subdivided by fitness level into Fit and Unfit categories based on established norms. The individuals were then followed over an average of 8 years to look at various health outcomes. Individuals in the Fit category had lower rates of death (from all causes) than individuals in the Unfit category and this relationship was consistent for all 3 body composition categories. This indicates that fatness is only a risk if a person is also unfit. It also indicates that if a person is thin, they can still be at increased risk if they are not fit. The differences between the groups can be easily seen in the graph below:

The researchers found similar results when the population was divided into categories of waist circumference. See graph below.

Sources:

• Lee, C.D., Blair, S.N., & Jackson, A.S. (1999). Cardiorespiratory fitness, body composition, and all-cause and cardiovascular disease mortality in men. American Journal of Clinical Nutrition, 69, 373-380.
• Wei, M., Kampert, J. B., Barlow, C. E., Nichaman, M. Z., Gibbons, L. W., Paffenbarger, R. S., Jr., & Blair, S. N. (1999). Relationship between low cardiorespiratory fitness and mortality in normal-weight, overweight, and obese men. Journal of The American Medical Association, 282, 1547-1553.

Web07-05: Development of Field Tests of Aerobic Fitness

While laboratory-based assessments of VO₂ max are highly accurate, they are expensive and impractical for most applications. Therefore, a number of "field-based" tests have been developed to make it easier to assess cardiovascular fitness in various settings and populations.

These tests are developed by having a large group of participants complete a given test along with a "lab-based" test similar to those described in Web08-03. Because each person is assessed with both approaches, it is possible to directly compare the results between the tests. With some statistical procedures, a "line of best fit" is created to represent the overall trends among the participants. An equation is determined that best represents the overall pattern in the data. Once the equation is developed, it is possible to estimate a person's fitness level just by completing the field test.

The accuracy of the estimates depends on the representative nature of the sample and the sample size. (Separate equations would typically be developed for different genders and would include age and other predictors such as weight in the equation). An example of the type of data used for these equations is presented below. Note that VO2 max is inversely (ie. negatively) related to mile run time (fit people run the mile in less time).

By using the procedures described above, scientists have developed equations that predict fitness levels with a reasonable degree of accuracy. However, because the fitness values are still estimates and because individuals may perform differently on different tests, results may vary across tests.

Web07-06: Cardiovascular Fitness Assessments

There are a number of different cardiovascular fitness assessments that are available for field based testing. The selected tests described here are those that are used in lab 7B.

The Twelve-Minute Run Test

• Locate an area where a specific distance is already marked, such as a school track or football field; or measure a specific distance using a bicycle or automobile odometer.
• Use a stopwatch or wristwatch to accurately time a twelve-minute period.
• For best results, warm up prior to the test, then run at a steady pace for the entire twelve minutes (cool down after the tests).
• Determine the distance you can run in twelve minutes in fractions of a mile. Look up score on chart.

The Step Test

• Warm up prior to exercise, and after finishing be sure to cool down.
• Step up and down on a twelve-inch bench for three minutes at a rate of twenty-four steps per minute. One step consists of four beats; that is, "up with the left foot, up with the right foot, down with the left foot, down with the right foot."
• Immediately after the exercise, sit down on the bench and relax. Don't talk. Locate your pulse or have another person locate it for you.
• Five seconds after the exercise ends, begin counting your pulse. Count the pulse for sixty seconds. Your score is your sixty-second heart rate.

The Astrand-Rhyming Bicycle Test

• Ride a stationary bicycle ergometer for six minutes at a rate of fifty pedal cycles per minute (one push with each foot per cycle). Cool down after the test.
• Set the bicycle at a work load between 300 and 1,200 kpm. For less fit or smaller people, a setting in the range of 300 to 600 is appropriate. Larger or fitter people will need to use a setting of 750 to 1,200. The work load should be enough to elevate the heart rate to at least 125 bpm but no more than 170 bpm during the ride.
• During the sixth minute of the ride (if the heart rate is in the correct range--see step 2), count the heart rate for the entire sixth minute. The carotid or radial pulse may be used. Your score is the heart rate for the last minute (60 seconds) of the ride.

The Walking Test

• Warm up, then walk one mile as fast as you can. Keep track of your time to the nearest second.
• Count your heart rate for 15 seconds immediately after the walk.

Mile Run Test (Same basic procedure as the 12 minute run.)

The Twelve-Minute Swim Test

• Use a pool that is measured in yards
• Use a stopwatch or wristwatch to accurately time a twelve-minute period.
• For best results, warm up prior to the test, then swim at a steady pace for the entire twelve minutes (cool down after the tests).
• Determine the distance you can swim in twelve minutes in increments of 50 yards. Look up score on chart

Web07-07: Supplemental Web Resources

American College of Sports Medicine - www.acsm.org

American Heart Association - http://www.americanheart.org

The Cooper Institute - http://www.cooperinst.org

Web07-08: Supplemental Readings

References new to 7e/14e

• ACSM. 2006. ACSM's Guidelines for Exercise Testing and Prescription. (7^th ed.). Philadelphia: Lippencott, Williams & Wilkins.
• Gulati, M. et al. 2005. The Prognostic value of a nomogram for exercise capacity in women. New England Journal of Medicine. 353(5): 468-475.
• Hills, A. P. et al., 2006. Validation of the intensity of walking for pleasure in obese adults. Preventive Medicine. 42(1): 47-50.
• Jurca, R. 2005. Assessing cardiorespiratory fitness without performing exercise testing. American Journal of Preventive Medicine. 29(3): 185-193.
• Centers for Disease Control and Prevention. Adult participation in recommended levels of physical activity--United States, 2001 and 2003 (2005). MMWR Morbidity and Mortality .Weekly.Report. (54): 208-1212.

Rererences from Past Editions

• American College of Sports Medicine. The Recommended Quantity and Quality of Exercise for Developing and Maintaining Cardiorespiratory and Muscular Fitness, and Flexibility in Healthy Adults. Medicine and Science in Sports and Exercise. Medicine and Science in Sports and Exercise, 30(6)(1998):975.
• American College of Sports Medicine. Exercise and Physical Activity for Older Adults. Medicine and Science in Sports and Exercise. Medicine and Science in Sports and Exercise, 30(6),(1998):992.
• Bouchard, C., et al. "Genetics of Aerobic and Anaerobic Performances." Exercise and Sport Sciences Reviews 20(1992):27.
• Bouchard, C., et al., eds. Physical Activity, Fitness, and Health. Champaign, IL: Human Kinetics Publishers, 1994.
• Bouchard, C. et al. Genetics of Fitness and Physical Performance. Champaign, IL: Human Kinetics, 1997.
• Brown, R., & J. Henderson. Fitness Running. Champaign, IL: Human Kinetics Publishers, 1994.
• "Can One Train Cardiorespiratory and Muscular Fitness Simultaneously?" (Editorial). Canadian Journal of Sport Science 16(1991):167-68.
• Cooper, K.H. The Aerobics Program for Total Well-Being. New York: M. Evans & Co., 1982.
• Couldry, W., et al. "Carotid vs. Radial Pulse Counts." Physician and Sportsmedicine 10(1982):67.
• Dowdy, D.B., et al. "Effects of Aerobic Dance on Physical Work Capacity, Cardiovascular Fitness, and Body Composition of Middle-aged Women." Research Quarterly 56(1985):227.
• Dunn, A. L. et al. Comparison of Lifestyle and Structured Interventions to Increase Physical Activity and Cardiorespiratory Fitness. Journal of the American Medical Association. 281(1999):327.
• Franklin, B. A. A Common Misunderstanding About Heart Rate and Exercise. ACSM's Health and Fitness. 2(1)(1998):18-19.
• Franks, B. D. Individualized recommendations for physical activity. President's Council on Physical Fitness and Sports Research Digest, 3(1)(1997):1.
• Haddock. B. L. et al. Cardiorespiratory Fitness and Cardiovascular Disease Risk Factors in Postmenopausal Women. Medicine and Science in Sports and Exercise. 30(6)(1998):1893.
• Meredith, M.D. "Activity or Fitness: Is the Process or the Product More Important for Public Health?" Quest 40(1988):180.
• Sedlock, D.A., et al. "Accuracy of Subject-Palpated Carotid Pulse after Exercise." Physician and Sportsmedicine 11(1983):106.
• Shephard, R. J., et al. "The Canadian Home Fitness Test." Sports Medicine 11(1991):358.
• U. S. Department of Health and Human Services. Healthy People 2010. (Conference Edition, in Two Volumes). Washington, DC: USDHHS, 2000.