Where Does Fitness Fit In?
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《新英格兰医药杂志》
Cardiorespiratory fitness, as measured by a number of relatively simple and inexpensive clinical maneuvers, provides strong and independent prognostic information about the overall risk of illness and death, especially that from cardiovascular causes. This relationship extends to men, women, and adolescents. It is valid in apparently healthy persons; in patients with a broad range of maladies, including several types of cancer and cardiovascular disease; and in at-risk patients with diabetes mellitus, the metabolic syndrome, and hypertension.1,2,3 However, despite the profoundly important prognostic information provided by simple clinical assessments of fitness, they are rarely used in the clinical setting and often ignored in the exercise-testing laboratory. The article by Gulati et al. in this issue of the Journal encourages us to rediscover the power of fitness in both apparently healthy populations and symptomatic referral populations.4
For fitness determinations to have broad clinical usefulness, normative values must be developed for commonly assessed demographic groups. Although normative values for men are well established, Gulati et al. address the historical lack of data for women. They present a nomogram for the assessment of normative fitness values for women across a broad age range, derived from data obtained as part of the community-based St. James Women Take Heart Project and validated in a multicenter, symptomatic referral population. This nomogram, similar to that previously obtained for men, now provides clinicians with a means of assessing a woman's relative fitness level using a readily obtainable, inexpensive clinical test. These data inform the care provider and the patient about the relative risk of disease and progression as well as the overall prognosis.
The clinical significance of the findings of Gulati et al. is greatly enhanced by the ease with which fitness can be measured. The exercise treadmill test is accessible and inexpensive, and most patients find it acceptable. The duration of exercise or estimated energy expenditure (expressed as metabolic equivalents, or MET, as used in this study, based on the speed and grade of the treadmill and the body mass of the subject) can readily be assessed. The authors' use of MET to construct their nomogram, as opposed to the time to exhaustion in a single standardized protocol, allows testing to be customized to accommodate the individual subject's ability to exercise and the clinician's preference as to the protocol used in the clinical setting.
A fitness determination puts powerful prognostic information into the hands of clinicians. Such information is of little clinical value unless it can be used to guide an effective intervention that substantially alters risk. Fortunately, in the case of cardiorespiratory fitness, such an intervention is readily available. Men who improve their fitness (as assessed by the duration of exercise) also decrease their cardiovascular risk. In one report, men had an 8 percent reduction in long-term cardiovascular risk for every minute of improvement in exercise capacity.5 The subjects in this observational study effectively halved their relative risk of death by abiding by the physical-activity recommendations of the American College of Sports Medicine and the Centers for Disease Control and Prevention: 30 minutes per day of at least moderate exercise on most or all days of the week.6 Recent observational data from the Nurses' Health Study and the Women's Health Study imply that similar relationships among physical activity, exercise, fitness, and outcome also hold for women and that even a small amount of exercise is protective.7 Since there are many determinants of cardiorespiratory fitness besides habitual exercise (e.g., genetics accounts for up to 50 percent of baseline fitness),8 it will be important to prove prospectively that regular exercise among relatively unfit persons actually prevents events in proportion to changes in fitness.
Although the currently available data do not demonstrate that fitness should be measured at each clinic visit, a patient's exercise history certainly can and should be obtained routinely. In a paradigm shift, many experts are advocating expanding the vital signs obtained during virtually all visits to include a risk behavior: smoking status. Given the strong effect of fitness on the risk of death from any cause, the risk of disability, the risk of death from cardiovascular causes, and longevity, perhaps assessment of this variable should also be made a routine component of all clinical assessments, by including a simple question regarding exercise habits during each office visit. Counseling sedentary persons to participate in an exercise program is acknowledged to be an important component of cardiovascular-risk management. As has been learned from efforts to reduce smoking, however, unless clinicians make it a regular practice to ask the relevant question and gather the data, they will fail to provide the consistent guidance and encouragement essential to changing patients' unhealthy lifestyle choices.
Exercise testing is routinely used to evaluate patients with symptoms. However, many exercise testing laboratories and clinicians focus on electrocardiographic findings and minimize the prognostic importance of the duration of exercise or total energy expenditure (as expressed in MET). Mark and Lauer decried this "widespread tendency to ignore exercise capacity in clinical management" in favor of focusing on ischemia and the prediction of angiographic anatomy.9 Extremely poor exercise capacity (such as observed in the cohorts evaluated by Gulati et al., in which some women had maximal exercise capacities of 1.2 to 1.4 MET) portends an extremely poor outcome. The predictive accuracy of ST-segment deviation is highly dependent on the duration of exercise. More broadly, it is imperative to concentrate on the overall patient in addition to the patency of the patient's coronary vasculature. Just as we now know that predicting coronary events depends not only on the presence of a single vulnerable plaque that is prone to rupture, but also on an expanded concept of the "vulnerable patient," so should we pay very close attention to the systemwide information reflected by a poor level of fitness and not focus solely on regional myocardial ischemia.
Gulati et al. observe that cardiorespiratory fitness deteriorates by approximately 1 percent per year of age. The knowledge of this decline is not new, but previous information was derived almost entirely from studies in men. By providing, for the first time, age-dependent nomograms for women, Gulati et al. identify differences in aging between the sexes (although whether these are significantly different is not addressed). This finding is important, since men and women of similar age and body weight differ in their exercise capacity or cardiorespiratory fitness, irrespective of whatever measure is used, as well as in other measurements of exercise physiology. Further research is needed to understand why the age-related deterioration in cardiorespiratory fitness is greater in women than in men.
There are a few limitations to the analysis provided by Gulati et al. As noted above, the authors did not provide a statistical comparison of the normative values for men and women to clarify the importance of this difference. In addition, they chose a cutoff point of 85 percent of the age-predicted exercise capacity to define populations for assessment of the hazard ratios for death from any cause and death from cardiovascular causes. Other than the obvious parallel to the 85 percent of predicted maximal heart rate often used to judge the adequacy of exercise stress, it is unclear why this value was chosen as a critical threshold. No sensitivity analysis is provided as justification.
Despite these concerns, the report by Gulati et al. provides important new normative values for women regarding exercise capacity and cardiorespiratory fitness and documents a strong relationship between these variables and the risk of death from any cause and from cardiovascular causes. By confirming the critical importance of fitness to health and longevity, the authors place a responsibility on clinicians to use this information for their patients' benefit. Given that such data are readily obtainable in the clinical setting (and often ignored when available on routine exercise testing), compliance should be fairly easy and inexpensive and represents an effective improvement in practice. We hope that this report will provide a stimulus to reintroduce fitness assessments into the routine clinical environment for both women and men.
Source Information
From the Division of Cardiovascular Medicine, Duke University Medical Center, Durham, N.C.
References
Department of Health and Human Services. Physical activity and health: a report of the Surgeon General. Atlanta: President's Council on Physical Fitness & Sports, National Center for Chronic Disease Prevention and Health Promotion, 1996.
Lee S, Kuk JL, Katzmarzyk PT, Blair SN, Church TS, Ross R. Cardiorespiratory fitness attenuates metabolic risk independent of abdominal subcutaneous and visceral fat in men. Diabetes Care 2005;28:895-901.
Blair SN, Kohl HW III, Paffenbarger RS Jr, Clark DG, Cooper KH, Gibbons LW. Physical fitness and all-cause mortality: a prospective study of healthy men and women. JAMA 1989;262:2395-2401.
Gulati M, Black HR, Shaw LJ, et al. The prognostic value of a nomogram for exercise capacity in women. N Engl J Med 2005;353:468-475.
Blair SN, Kampert JB, Kohl HW III, et al. Influences of cardiorespiratory fitness and other precursors on cardiovascular disease and all-cause mortality in men and women. JAMA 1996;276:205-210.
Pate RR, Pratt M, Blair SN, et al. Physical activity and public health: a recommendation from the Centers for Disease Control and Prevention and the American College of Sports Medicine. JAMA 1995;273:402-407.
Hu FB, Willett WC, Li T, Stampfer MJ, Colditz GA, Manson JE. Adiposity as compared with physical activity in predicting mortality among women. N Engl J Med 2004;351:2694-2703.
Bouchard C, Rankinen T, Chagnon YC, et al. Genomic scan for the maximal oxygen uptake and its response to training in the HERITAGE Family Study. J Appl Physiol 2000;88:551-559.
Mark DB, Lauer MS. Exercise capacity: the prognostic variable that doesn't get enough respect. Circulation 2003;108:1534-1536.(William E. Kraus, M.D., a)
For fitness determinations to have broad clinical usefulness, normative values must be developed for commonly assessed demographic groups. Although normative values for men are well established, Gulati et al. address the historical lack of data for women. They present a nomogram for the assessment of normative fitness values for women across a broad age range, derived from data obtained as part of the community-based St. James Women Take Heart Project and validated in a multicenter, symptomatic referral population. This nomogram, similar to that previously obtained for men, now provides clinicians with a means of assessing a woman's relative fitness level using a readily obtainable, inexpensive clinical test. These data inform the care provider and the patient about the relative risk of disease and progression as well as the overall prognosis.
The clinical significance of the findings of Gulati et al. is greatly enhanced by the ease with which fitness can be measured. The exercise treadmill test is accessible and inexpensive, and most patients find it acceptable. The duration of exercise or estimated energy expenditure (expressed as metabolic equivalents, or MET, as used in this study, based on the speed and grade of the treadmill and the body mass of the subject) can readily be assessed. The authors' use of MET to construct their nomogram, as opposed to the time to exhaustion in a single standardized protocol, allows testing to be customized to accommodate the individual subject's ability to exercise and the clinician's preference as to the protocol used in the clinical setting.
A fitness determination puts powerful prognostic information into the hands of clinicians. Such information is of little clinical value unless it can be used to guide an effective intervention that substantially alters risk. Fortunately, in the case of cardiorespiratory fitness, such an intervention is readily available. Men who improve their fitness (as assessed by the duration of exercise) also decrease their cardiovascular risk. In one report, men had an 8 percent reduction in long-term cardiovascular risk for every minute of improvement in exercise capacity.5 The subjects in this observational study effectively halved their relative risk of death by abiding by the physical-activity recommendations of the American College of Sports Medicine and the Centers for Disease Control and Prevention: 30 minutes per day of at least moderate exercise on most or all days of the week.6 Recent observational data from the Nurses' Health Study and the Women's Health Study imply that similar relationships among physical activity, exercise, fitness, and outcome also hold for women and that even a small amount of exercise is protective.7 Since there are many determinants of cardiorespiratory fitness besides habitual exercise (e.g., genetics accounts for up to 50 percent of baseline fitness),8 it will be important to prove prospectively that regular exercise among relatively unfit persons actually prevents events in proportion to changes in fitness.
Although the currently available data do not demonstrate that fitness should be measured at each clinic visit, a patient's exercise history certainly can and should be obtained routinely. In a paradigm shift, many experts are advocating expanding the vital signs obtained during virtually all visits to include a risk behavior: smoking status. Given the strong effect of fitness on the risk of death from any cause, the risk of disability, the risk of death from cardiovascular causes, and longevity, perhaps assessment of this variable should also be made a routine component of all clinical assessments, by including a simple question regarding exercise habits during each office visit. Counseling sedentary persons to participate in an exercise program is acknowledged to be an important component of cardiovascular-risk management. As has been learned from efforts to reduce smoking, however, unless clinicians make it a regular practice to ask the relevant question and gather the data, they will fail to provide the consistent guidance and encouragement essential to changing patients' unhealthy lifestyle choices.
Exercise testing is routinely used to evaluate patients with symptoms. However, many exercise testing laboratories and clinicians focus on electrocardiographic findings and minimize the prognostic importance of the duration of exercise or total energy expenditure (as expressed in MET). Mark and Lauer decried this "widespread tendency to ignore exercise capacity in clinical management" in favor of focusing on ischemia and the prediction of angiographic anatomy.9 Extremely poor exercise capacity (such as observed in the cohorts evaluated by Gulati et al., in which some women had maximal exercise capacities of 1.2 to 1.4 MET) portends an extremely poor outcome. The predictive accuracy of ST-segment deviation is highly dependent on the duration of exercise. More broadly, it is imperative to concentrate on the overall patient in addition to the patency of the patient's coronary vasculature. Just as we now know that predicting coronary events depends not only on the presence of a single vulnerable plaque that is prone to rupture, but also on an expanded concept of the "vulnerable patient," so should we pay very close attention to the systemwide information reflected by a poor level of fitness and not focus solely on regional myocardial ischemia.
Gulati et al. observe that cardiorespiratory fitness deteriorates by approximately 1 percent per year of age. The knowledge of this decline is not new, but previous information was derived almost entirely from studies in men. By providing, for the first time, age-dependent nomograms for women, Gulati et al. identify differences in aging between the sexes (although whether these are significantly different is not addressed). This finding is important, since men and women of similar age and body weight differ in their exercise capacity or cardiorespiratory fitness, irrespective of whatever measure is used, as well as in other measurements of exercise physiology. Further research is needed to understand why the age-related deterioration in cardiorespiratory fitness is greater in women than in men.
There are a few limitations to the analysis provided by Gulati et al. As noted above, the authors did not provide a statistical comparison of the normative values for men and women to clarify the importance of this difference. In addition, they chose a cutoff point of 85 percent of the age-predicted exercise capacity to define populations for assessment of the hazard ratios for death from any cause and death from cardiovascular causes. Other than the obvious parallel to the 85 percent of predicted maximal heart rate often used to judge the adequacy of exercise stress, it is unclear why this value was chosen as a critical threshold. No sensitivity analysis is provided as justification.
Despite these concerns, the report by Gulati et al. provides important new normative values for women regarding exercise capacity and cardiorespiratory fitness and documents a strong relationship between these variables and the risk of death from any cause and from cardiovascular causes. By confirming the critical importance of fitness to health and longevity, the authors place a responsibility on clinicians to use this information for their patients' benefit. Given that such data are readily obtainable in the clinical setting (and often ignored when available on routine exercise testing), compliance should be fairly easy and inexpensive and represents an effective improvement in practice. We hope that this report will provide a stimulus to reintroduce fitness assessments into the routine clinical environment for both women and men.
Source Information
From the Division of Cardiovascular Medicine, Duke University Medical Center, Durham, N.C.
References
Department of Health and Human Services. Physical activity and health: a report of the Surgeon General. Atlanta: President's Council on Physical Fitness & Sports, National Center for Chronic Disease Prevention and Health Promotion, 1996.
Lee S, Kuk JL, Katzmarzyk PT, Blair SN, Church TS, Ross R. Cardiorespiratory fitness attenuates metabolic risk independent of abdominal subcutaneous and visceral fat in men. Diabetes Care 2005;28:895-901.
Blair SN, Kohl HW III, Paffenbarger RS Jr, Clark DG, Cooper KH, Gibbons LW. Physical fitness and all-cause mortality: a prospective study of healthy men and women. JAMA 1989;262:2395-2401.
Gulati M, Black HR, Shaw LJ, et al. The prognostic value of a nomogram for exercise capacity in women. N Engl J Med 2005;353:468-475.
Blair SN, Kampert JB, Kohl HW III, et al. Influences of cardiorespiratory fitness and other precursors on cardiovascular disease and all-cause mortality in men and women. JAMA 1996;276:205-210.
Pate RR, Pratt M, Blair SN, et al. Physical activity and public health: a recommendation from the Centers for Disease Control and Prevention and the American College of Sports Medicine. JAMA 1995;273:402-407.
Hu FB, Willett WC, Li T, Stampfer MJ, Colditz GA, Manson JE. Adiposity as compared with physical activity in predicting mortality among women. N Engl J Med 2004;351:2694-2703.
Bouchard C, Rankinen T, Chagnon YC, et al. Genomic scan for the maximal oxygen uptake and its response to training in the HERITAGE Family Study. J Appl Physiol 2000;88:551-559.
Mark DB, Lauer MS. Exercise capacity: the prognostic variable that doesn't get enough respect. Circulation 2003;108:1534-1536.(William E. Kraus, M.D., a)