It has been estimated that as many as 250,000 deaths per year in the United States are attributable to lack of regular physical activity.¹⁸ Ongoing longitudinal studies have provided consistent evidence of varying strength documenting the protective effects of activity for a number of chronic diseases, including CHD,⁴,⁵,⁸, ⁹, ¹⁰,¹²,¹⁹,²⁰ type 2 diabetes,²⁰, ²¹, ²², ²³, ²⁴ hypertension,²⁵ osteoporosis,²⁶ and site-specific cancers.²⁷ In contrast, low levels of physical fitness or activity are consistently associated with higher cardiovascular and all-cause mortality rates.²,⁴,⁵,¹⁹,²⁰,²⁸ Mid-life increases in physical activity, through change in occupation or recreational activities, are associated with a decrease in mortality rates.²⁹

The landmark epidemiologic work of the late Ralph Paffenbarger and associates among Harvard alumni⁶,²⁹, ³⁰, ³¹, ³², ³³ has been particularly persuasive in support of physical activity and therefore the development of the CDC, AHA, IOM, and ACSM guidelines. Table 37-1 illustrates the rates and relative risks of death over a 9-year period among 11,864 Harvard alumni by patterns of physical activity. Several findings in Table 37-1 are particularly noteworthy. The largest benefits in terms of mortality appear to occur by engaging in moderate activity levels; moderate is generally defined as activity performed at an intensity of 3 to 6 metabolic equivalents (METs) (a multiple of the resting metabolic rate), approximately equivalent to brisk walking for most adults.³⁴ Note also that regular moderate walking or sports participation is associated with 30% to 40% reductions in mortality compared with more sedentary individuals (relative risk of death 0.60 to 0.70). Likewise, the physical activity index, expressed as kilocalories per week (the sum of walking, stair climbing, and sports participation) suggests that a 40% reduction in mortality occurs by engaging in modest levels of activity (1,000 to 2,000 kcal/week, equivalent to three to five 1-hour sessions of activity), whereas only minimal additional benefits are achieved by engaging in greater-intensity activity. These findings agree closely with earlier results among 16,936 Harvard alumni assessed in the early 1960s and followed for all-cause mortality for nearly 20 years.³⁰ Similar results have been reported from large studies that have followed subjects for CHD morbidity and mortality in the range of 10 to 20 years among British civil servants,³⁵,³⁶ U.S. railroad workers,³⁷ San Francisco longshoremen,³³ nurses,³⁸, ³⁹, ⁴⁰ physicians,⁴¹ U.S. Veterans,⁴² and other cohorts (for review, see Kohl¹⁹ or Pedersen and Saltin⁴³). Clearly, the evidence linking a physically active lifestyle and cardiovascular health is substantial.

A growing number of studies have been published in which physical fitness, determined by standardized exercise testing, was determined among large samples of men and women who have been followed for the incidence of CHD morbidity and mortality for up to 10 years.⁴²,⁴⁴, ⁴⁵, ⁴⁶, ⁴⁷, ⁴⁸, ⁴⁹ Each of these studies demonstrated that higher levels of fitness were associated with lower rates of CHD or all-cause mortality. It is important to note that these associations appear to be independent of other CHD risk factors. Also important is that the low levels of fitness in these studies did not appear to be associated with subclinical disease.

In a classic analysis, Blair et al.⁴⁴ assessed fitness by treadmill performance in 10,244 men and 3,120 women and followed them for 110,482 person-years (averaging >8 years) for all-cause mortality. These results are presented in Table 37-2. Mortality rates were lowest (18.6 per 10,000 man-years) among the most fit and highest (64.0) among the least fit men, with the corresponding rates among the women 8.5 and 39.5 per 10,000 person-years, respectively. These findings closely parallel an earlier report among asymptomatic men from the Lipid Research Clinics (LRC) Mortality Follow-up Study,⁵⁰ in which each 2-SD decrement in exercise capacity was associated with a two- to five-fold higher CHD or all-cause death rate. More recent studies, including one from the LRC,⁵¹ have reinforced the fact that these findings also apply to women who are healthy at the time of evaluation. Gulati et al.⁵² suggested that the strength of exercise capacity in predicting risk of mortality was even greater among women than men, reporting a 17% reduction in risk for every 1-MET increase in fitness. In the LRC, nearly 3,000 asymptomatic women underwent exercise testing and were followed for up to 20 years.⁵¹ A 20% decrease in survival was observed for every 1-MET decrement in exercise capacity. This study also pointed out the relative weakness of ischemic electrocardiogram (ECG) responses in predicting cardiovascular and all-cause mortality among women.

This issue has also recently been addressed in clinical populations, for example, patients referred for exercise testing for clinical reasons.⁴²,⁴⁵, ⁴⁶, ⁴⁷,⁵²,⁵³ In a study performed among the U.S. Veterans, 6,213 men underwent maximal exercise testing for clinical reasons and were followed for a mean of 6.2 years.⁴⁵ The subjects were classified into five categories by gradients of fitness. After adjustment for age, the researchers observed that the largest gains in terms of mortality were achieved between the lowest fitness group and the next lowest fitness group. Figure 37-1 illustrates the age-adjusted relative risks associated with the different categories of fitness. Among both normal subjects and those with cardiovascular disease, the least fit individuals had more than four times the risk of all-cause mortality compared with the most fit individuals. Importantly, an individual’s fitness level was a stronger predictor of mortality than established risk factors such as smoking, high blood pressure, high cholesterol, and diabetes. Over the past few years, other cohorts, such as those from the Cleveland Clinic⁵³ and the Mayo Clinic,⁴⁶,⁴⁷ have documented the importance of exercise capacity as a predictor of mortality among clinically referred populations. These clinically based studies confirm earlier observations from the Aerobics Center Longitudinal Study,⁴⁴ Framingham,⁵⁴ and the LRC Trial⁵⁰ among asymptomatic populations, underscoring the fact that fitness level has a strong influence on the incidence of cardiovascular and all-cause morbidity and mortality.

Over the last 15 years, numerous consensus guidelines have been published from organizations concerning physical activity and health, including the World Health Organization, ACSM, AHA, CDC, and European Working Group on Exercise Physiology and Rehabilitation.¹, ², ³, ⁴, ⁵,⁷,⁵⁵,⁵⁶ Among the most prominent of these was the U.S. Surgeon General’s Report on Physical Activity and Health published in 1996. This document represented the strongest policy statement ever made by the U.S. Government concerning physical activity.⁵ It represented a historic turning point redefining exercise as a key component to health promotion and disease prevention. The federal government mounted a multi-year educational campaign based on this report. In this report, the epidemiologic evidence supporting physical activity in the prevention of CHD morbidity and mortality is reviewed in detail. The document also outlines the quantity of exercise necessary to achieve these benefits. It is suggested that each person perform a moderate amount of activity daily, with the amount of activity emphasized rather than the intensity. The concept is that this offers people more opportunities for activities that fit into their daily lives. It is suggested that this moderate amount of activity be performed for 30 minutes or more on most, and preferably all, days of the week. These activities can take the form of brisk walking, yard work or other household chores, jogging, or a wide variety of recreational activities. Repeated intermittent or shorter bouts of activity (e.g., 10 minutes), including occupational, nonoccupational, or tasks of daily living, have similar cardiovascular and health benefits if performed at a level of moderate intensity with an accumulated duration of at least 30 minutes per day. Individuals who already meet these standards receive additional benefits from increasing this amount to more vigorous activity.

The concept that all individuals should incorporate 30 minutes of physical activity into their daily lives is a consistent theme in all of the recent consensus documents on physical activity and health throughout the world.¹, ², ³, ⁴, ⁵,⁷,⁵⁵,⁵⁶ Despite this evidence, however, most adults in Western societies remain effectively sedentary,⁷,¹⁷,¹⁸ and only a minority of patients who are eligible are referred to a cardiac rehabilitation program.¹³ Given the dramatic increases over the last two decades in the prevalence of overweight, obesity, diabetes, and other conditions related in part to lack of physical activity,²⁸ the nurse or other health care provider’s role is more critical than ever in terms of encouraging patients to become more physically active, and to develop strategies that promote the adoption of physically active lifestyles in all their patients.

A noteworthy theme that is consistent in each of the aforementioned documents is that considerable health benefits are derived from moderate levels of activity; it is generally not necessary to engage in vigorous, sustained activity to derive many of these benefits. Before the release of these reports in the mid 1990s, consensus documents generally promoted the concept that exercise was thought to be effective only if an improvement in some measure of cardiopulmonary function was observed. In recent years, the philosophy on exercise as a means to this end (“fitness” measured by exercise capacity) has changed significantly. It is now appreciated that substantial health benefits can be achieved through relatively modest amounts of regular exercise, regardless of whether exercise results in a measurable improvement in exercise capacity. Epidemiologic studies have shown that death rates from cardiovascular and all causes are considerably lower even among people who engage in modest amounts of exercise, less than the threshold that was generally thought necessary to increase exercise capacity.¹, ², ³, ⁴, ⁵,⁷,⁵⁵,⁵⁶ It is important for health professionals to be aware of the distinction between “health” and “fitness” when making activity recommendations to patients with cardiovascular disease, those at high risk for its development, and healthy adults. In addition to cardiopulmonary fitness, measures of fat and lean weight, bone density, glucose and insulin metabolism, blood lipid and lipoprotein metabolism, and quality of life should be included under the category of “health.” A favorable profile for these variables represents a clear advantage in terms of health outcomes as assessed by morbidity and mortality statistics.

During the 1970s and 1980s, numerous controlled trials addressed whether participation in a rehabilitation program influenced morbidity or mortality in patients with CHD. Although the results of these trials were inconclusive independently, most demonstrated a favorable trend for a lower mortality rate among patients who exercised compared with control subjects. For example, the National Exercise and Heart Disease Project was a controlled randomized trial in the United States on the effects of prescribed supervised exercise involving 651 men with acute MI.⁵⁷ The cumulative 3-year total mortality rates in this study were 7.3% and 4.6% for the control and exercise groups, respectively, whereas the rates for recurrent MI were 7.0% and 5.4%, respectively. Although this represented 37% and 24% reductions in mortality and reinfarction rates, respectively, for the exercise groups, more than twice as many patients would have been necessary in the study for these differences to be statistically significant. The lack of adequate sample size in this study is typical of the secondary prevention trials that have assessed mortality; although the trends are generally favorable, few have independently demonstrated that patients randomized to an exercise program have a significantly lower mortality compared with control subjects. However, two cardiac rehabilitation trials in Europe were noteworthy for their favorable morbidity and mortality outcomes. Vermuelen et al.,⁵⁸ in a study involving fewer than 100 patients, found that a 6-week rehabilitation program including comprehensive risk factor reduction and exercise resulted in a 50% lower rate of combined CHD morbidity and mortality in the rehabilitation compared with the control patients over a 5-year follow-up period. In the second of these multiple risk factor intervention trials, Kallio et al.⁵⁹ studied 375 consecutive male and female post-MI patients younger than 65 years in two clinical centers in Finland. After 3 years of follow-up, the cumulative CHD mortality rate was significantly lower in the intervention group compared with the control group (18.6% vs. 29.4%). This difference primarily reflected a reduction in sudden death in the intervention group during the first 6 months after MI. A favorable trend toward reduction in nonfatal reinfarctions also was observed in the intervention group.

An alternative but less rigorous scientific approach, in the absence of a definitive clinical trial, is to pool data from existing long-term, randomized, secondary prevention trials in which exercise training was a component. Several noteworthy meta-analyses have been published in which data from randomized clinical trials were pooled using the intention-to-treat principle.⁹,¹⁰,⁶⁰ In the trials included in these meta-analyses, intervention consisted of either a formal exercise program or exercise advice, generally in combination with multiple risk factor management, making it impossible to determine the independent contribution of exercise to subsequent morbidity and mortality. Nevertheless, patients randomized to active cardiac rehabilitation programs after an MI had statistically significant reductions of approximately 25% in 1- to 3-year rates of fatal cardiovascular events and total mortality compared with control patients (Table 37-3). However, significant differences in general were not found in the rate of nonfatal recurrent reinfarctions in patients undergoing intervention compared with control patients.