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High Cardiorespiratory Fitness
Len Kravitz, Ph.D.

Study Reviewed:
Lee, D-c, Artero, E.G., Sui, X, and Blair, S.N. (2010) Review: Mortality trends in the general population: the importance of cardiorespiratory fitness. Journal of Psychopharmacology, 24(11), 27-35.

Introduction: New Impact Goals and Cardiorespiratory Fitness
Recently a task force of scientists selected by the American Heart Association (AHA) introduced the 2020 U.S. 'Impact Goals' for cardiovascular health and disease reduction (Llyod-Jones, 2010). Ideal cardiovascular health includes four health behaviors (non-smoking, BMI <25 kg/m2, physical activity {150 min/wk of moderate intensity exercise or 75 min/wk of vigorous intensity exercise or a combination}, and consumption of a diet that promotes cardiovascular health {emphasis on a low glycemic load, high fiber, high marine omega-3 fatty acid, high polyunsaturated to saturated fat ratio, and low trans fat content} and three health factors (total cholesterol <200 mg/dL, fasting blood glucose <100 mg/dL, and <120/80 mmHG for blood pressure). The new Impact Goals document also declares that as the amount of physical activity increases through higher intensity, greater frequency, and/or longer duration, men and women experience much healthier lives. Coinciding with these new AHA goals is new evidence suggesting that low cardiorespiratory fitness (CRF) is an equally strong predictor of cardiovascular disease (CVD) and other health causes of mortality (referred to as all-cause mortality), as are well-established risk factors such as smoking, obesity, hypertension and diabetes (Lee et al., 2010). CRF can be defined as the ability of the respiratory, circulatory and muscular systems to consume, distribute and utilize oxygen during continuous physical activity (Lee et al.). It is measured in milliliters of oxygen per kilogram of body weight (ml O2/kg/min). This research column will review the new research examining the importance of CRF for CVD disease risk reduction.

CRF and Mortality
Lee et al. (2010) summarize several research studies that have demonstrated compellingly that moderate to high levels of CRF are associated with a reduced risk of CVD. In a recent and original meta-analysis (study that combines results of several investigations) on CRF and mortality, Kodama et al. (2009) reviewed 33 studies comprising 102,980 men and women participants (6910 all-cause deaths) and 84,323 participants (4485 CVD events). From this analysis, Kodama and colleagues summarized that each 1-MET increase in CRF is associated with a 13% and 15% risk reduction from all-cause mortality and CVD events, respectively. See Sidebar 1 for more on the MET. Persons with low CRF have a higher risk of all causes of mortality and CVD events, as compared to those individuals with moderate to high levels of CRF. Kodama and colleagues also clarify that this CVD risk reduction observed with higher CRF levels is present regardless of a person's age, sex, body mass index and smoking status.

Does a Change in CRF Affect Risk of Mortality?
With the risk of low levels of CRF to CVD well established, a meaningful question is whether improvements in CRF will also result in positive changes in CVD risk. Erikssen et al. (1988) followed 2014 health men (40-60 years at baseline) for 7 years. The researchers report that improvements in CRF within the 7 years were associated with significant risk reduction from all causes of mortality. Lee et al. (2010) cite other research that confirms improvement of low levels of CRF to moderate and high levels does reduce the risk of CVD and other causes of mortality decreases. It is important that exercise professionals inform their clients that by improving their fitness level they are actually developing healthier lives and reducing disease risk. Erikssen and colleagues emphasize that even small improvements in CRF result in significant CVD risk reductions, which is a really an encouraging incentive to share with clients.

What are the Biological Mechanisms that Explain how CRF reduces CVD Risk.
Lee et al. (2010) indicate there are several mechanisms that explain how improved CRF reduces the risk for CVD and all causes of mortality. In highlighting a few of these key mechanisms, the relationship of CRF to insulin resistance (a condition in which cells of the body become resistance to the effects of insulin, impairing the cells ability to take up and use glucose) comes to the forefront. Higher levels of CRF improve insulin sensitivity, thus improving the cell's ability to use glucose as a fuel and helping to prevent or manage type 2 diabetes. Secondly, Lee and colleagues recap data that show persons with higher CRF have a lowered risk of all variables in metabolic syndrome (waist circumference, triglycerides, HDL-cholesterol, blood pressure, fasting blood glucose). Persons with metabolic syndrome are very likely to develop CVD and diabetes.

Biological Means how Improved CRF Reduces CVD Risk
Improved insulin sensitivity
Decreased apoliprotein B (a CVD marker)
Decreased blood pressure (when elevated)
Enhanced heart autonomic nervous system function
Reduced risk of metabolic syndrome
Decreased body fat
Lowered LDL-C (bad cholesterol)
Elevated HDL-C (good cholesterol)
Decreased abdominal obesity
Enhanced heart autonomic nervous system function

Final CRF Improvement Thoughts
Recent studies show that CRF is an excellent measure of several bodily functions highly associated with CVD and all causes of mortality. According to the data, one of the most important strategies that personal trainers can incorporate in their clients' training is a goal to increase CRF, as it is likely to bring substantial benefits to health. Get moving a little faster!

Side Bar 1. Five Questions and Answers on CRF Fitness
1) What is a MET and how is it used? A MET is a standardized unit of measurement for expressing exercise workload. The estimated energy expenditure cost at rest is one MET, which is equal to 3.5 ml O2/kg/min. In some exercise training situations, such as cardiac rehabilitation and research studies, exercise professionals design persons' workout intensities using METs.
2) Is there a gender difference in men and women and maximal aerobic capacity? Yes, on average maximal aerobic capacity in women is roughly 2 METs lower than men due to smaller muscle mass, lower hemoglobin and blood volume, and smaller stroke volume compared with men (Lee et al., 2010).
3) How does obesity affect CRF?
Wang et al. (2010) have shown that regardless of race, gender or ethnicity, people who are obese have a significantly lower CRF (~15% lower) than non-obese adults.
4) What are the main limitations to CRF?
The main limitations to CRF are often referred to as central and peripheral factors.
Central factors include oxygen delivery to muscles during endurance exercise, which may be limited by pulmonary diffusion (exchange of oxygen and carbon dioxide between the lungs and the blood), maximal cardiac output (the product of heart rate and stroke volume), and the blood's oxygen carrying capacity. Peripheral factors refer the ability of exercising muscles to extract and utilize oxygen, which has been transported by the cardiorespiratory system.
5) What is the best way to improve CRF?
ACSM advocates that greater improvements in CRF can be attained with 3 to 5 days a week of cardiovascular exercise at 64% to 94% of maximum heart rate (Whaley, 2007). Continuous training and interval training programs are encouraged to last between 20 and 60 minutes. To achieve higher levels of CRF, ACSM suggests that progressive increases in intensity and duration must be incorporated into the exercise program.
Erikssen, G., Liestol, K., Bjornhold, J., Thaulow, E., Sandvik, L., and Erikssen, J. (1998). Changes in physical fitness and changes in mortality. Lancet, 352, 759-762.
Kodama, S., Saito, K., Tanaka, S., Maki, M., Yachi, Y., et al. (2009) Cardiorespiratory fitness as a quantitative predictor of all-cause mortality and cardiovascular events in healthy men and women; a meta-analysis. Journal of the American Medical Association, 301, 2024-2035.
Llyod-Jones, D.M., Hong, Y., Labarthe, D., Mozaffarin, D. et al. (2010). Defining and setting national goals for cardiovascular health promotion and disease reduction: the American Heart Association's strategic Impact Goal through 2020 and beyond. Circulation, 121, 586-613.
Wang, C-Y., Haskell, W.L., Farrell, S.W., Lamonte, M.J. et al. (2010). Cardiorespiratory fitness levels among US adults 20-49 years of age: Findings from the 1999-2004 National Health and Nutrition Examination Survey. American Journal of Epidemiology, 171(4), 426-435.
Whaley, M.H. (2007). ACSM's Guidelines for Exercise Testing and Prescription, Seventh Edition. Lippincott Williams & Wilkins
Len Kravitz, PhD, is the program coordinator of exercise science and a researcher at the University of New Mexico, Albuquerque, where he won the Outstanding Teacher of the Year award. He has received the prestigious Can-Fit-Pro Lifetime Achievement Award and the 2010 Aquatic Exercise Association Global Award.