Effect of habitual physical activity and physical fitness on coronary heart...

Literature defining the benefits of habitual physical activity and physical fitness on coronary heart disease and heart attack in middle-aged adult males was reviewed. Considerable epidemtologi-cal research supports the hypothesis that physical inactiviiy and low levels of physical fitness are important risk factors for coronary heart disease and heart attack. Moderate levels of physical activity and physical fitness seem to provide major health benefits. The risk of heart attack during physical activity was also reviewed. Although there is a transient increase in the incidence of heart attack during vigorous physical activity, habitual activity was associated with an overall reduced risk of heart attack.

It is estimated that approximately 1 million people die of various forms of cardiovascular disease every year. Heart attack Is the leading cause of death in America today. Estimates from the American Heart Association (American Heart Association, 1991)) are that as many as 1.5 million persons will have a heart attack each year and that more than 500,000 of them will die. The AHA identifies high blood pressure, elevated blood cholesterol, and cigarette smoking as major risk factors for coronary heart disease. Physical inactivity Is identified as a contributing risk factor. However, the evidence Is rapidly accumulating to establIsh physical in activity as a significant risk factor. The purpose of this paper was to review those studies, primarily within the past decade, which identify physical activity and moderate levels of physical fitness as significant factors in the prevention of CHD and heart attack. Most of these studies are epidemiological in design and focus on middle-aged males as subjects. For a meaningful interpretation of thIs literature, it is important to distinguish between the terms "physical activity" and "exercise." The recommendations of Caspersen. Powell, and Christenson (1985) are appropriate for defining these terms which are often confused and sometimes used interchangeably. Physical activity is defined as any bodily movement produced by skeletal muscles that results in energy expenditure. Exercise is a subset of physical activity with the same characteristics plus it is planned, structured, and repetitive and has as a final or intermediate objective the improvement or maintenance of physical fitness.

Health outcomes associated with physical activity patterns among large cohorts of San Francisco longshoremen and Harvard alumni have been studied by Paffenbarger and Hale (1975). They followed 6,351 longshoremen, 35 to 74 years of age upon entry, for 22 years or to death or to age 75. Their long shoring experience was computed in terms of work-years according to categories of high, medium. and low caloric output. Intensity of physical effort was recognized by union regulations which limited each working hour to 55% labor and 45% rest for those in the high calorie category. Those in the moderate or medium work category worked 65% of each hour and rested 35%, while those in the low caloric category worked 75% of each hour and rested 25%. Individual work assignments were reclassified annually to allow for effect of Job transfers. The age-adjusted coronary death rate for the high-activity category was 26.9 per 10,000 work-years, and the medium and low categories had rates of 46.3 and 49.0. The authors concluded that vigorous physical exercise, as defined by an apparent threshold or critical level of energy output, was associated with reduced risk of coronary mortality. particularly the sudden-death syndrome.

Physical activity and other lifestyle characteristics of a more sedentary population were also analyzed (Paffenbarger, Hyde. Wing, & Hsieh, 1986). Almost 17,000 Harvard alumni, aged 35-74. were studied for relations to rates of mortality from all causes and for influences on length of life. Exercise reported as walking. stair climbing. and sports play related inversely to total mortality. primarily to death due to cardiovascular or respiratory causes. Death rates declined steadily as energy expended on such activity increased from less than 500 to 3,500 kilocalories per week. Rates were one-quarter to one-third lower among alumni expending 2.000 or more kilocalories during exercise per week than among less active men. With or without consideration of hypertension. cigarette smoking. extreme gains in body weight, or early parental death. alumni mortality rates were significantly lower among the physically active. Further analysis of the Harvard alumni data showed that habitual post-college exercise. not student sports play, predicts low coronary heart disease risk (Paffenbarger, Hyde, Wing, & Steinmetz, 1984). Sedentary alumni, even ex-varsity athletes, have high risks. Sedentary students becoming physically active alumni acquire low risk. Thus, despite socioeconomic and lifestyle differences between longshoremen and Harvard men, within each population, more active persons had less coronary disease.

Debate currently centers around whether physical activity sufficient to increase physical fitness is required for health benefits (Blair, 1985; LaPorte et al., 1984; LaPorte, Dearwater, Cauley, Slemenda. & Cook, 1985). Since physical activity is an important determinant of physical fitness. then to some extent, fitness is an objective marker for physical activity. Because physical fitness can be measured more objectively than physical activity, research studies that utilize the measurement of physical fitness are important. In this paper. physical fitness refers to physical work capacity (PWC). PWC is the maximal rate at which a person can expend energy. It is measured in the laboratory by maximal oxygen consumption. PWC also can be reliably estimated by submaximal procedures.

Slattery and Jacobs (1988) studied the relation between physical fitness and cardiovascular disease mortality in United States raft-road workers. A cohort of 3,043 white, middle-aged men initially aged 22 to 79 years were first examined in 1957-1960 and reexamined in 1962-1964. Men with clinically diagnosed cardiovascular disease (N=465) were excluded from the study. This cohort was followed until death or 1977. Physical fitness was ascertained by a sub-maximal treadmill test. Results from the study suggested that middle-aged men with lower levels of physical fitness, as shown by higher sub-maximal exercise test heart rates, are at greater risk of dying of coronary heart disease, cardiovascular disease, and all causes.

Healthy male factory workers aged 40 to 55 were examined by Sobolski et al. (1987) in the Belgium physical fitness study. This prospective study of 2,363 males followed the subjects for 5 years. Physical activity on the Job and physical activity during leisure time were assessed with questionnaires. Physical working capacity was estimated from a graded submaximal bicycle exercise test. Physical working capacity was defined as the work load at a heart rate of 150 beats/minute. The results showed that occupational physical activity and leisure time physical activity did not contribute independently to the prediction of subsequent myocardial infarction. Rather, it was physical fitness, which probably reflects characteristics other than solely physical activity patterns, that independently predicted future coronary events.

Ekelundet al. (1988) studied 4,276 asymptomatic men aged 30 to 69 years of age. These men were followed for an average of 8.5 years. Examinations at baseline included assessment of conventional coronary risk factors and a submaximal treadmill exercise test. The heart rate during submaximal exercise and the duration of exercise were used as measures of physical fitness. In this group of healthy men the fitness level was closely related to regular physical activity as reported by the participants. This finding suggested that regular physical activity was more important than genetic factors in determining the level of fitness and, therefore, might be an important factor in reducing the risk of death from coronary heart disease. The low-fit men In this study were 8.5 times more likely to die of cardiovascular disease than the high-fit men. The investigators concluded that a lower level of physical fitness is associated with a higher risk of death from coronary heart disease and cardiovascular disease in clinically healthy men, independent of conventional coronary risk factors.

Physical fitness was assessed by maximal treadmill tests in 10,224 men by Blair et al. (1989). Average follow-up was slightly more than 8 years. Maximal treadmill test results were used to group the men into a fitness category. The bottom 20% were classified as low-fit, the middle 40% as moderate-fit and the top 40% as high-fit. Participants In the low-fit category were three times as likely to die from cardiovascular disease than men in the moderate-fit group, 24.6 vs. 7.8 age-adjusted deaths per 10,000 person-years, respectively. The lowest death rates, 3.1 per 10,000 person-years, were seen in the high-fit group. Another important finding in this study was that higher levels of physical fitness were beneficial even in persons with other cardiovascular risk factors. The investigators concluded that moderate levels of physical fitness, obtainable by most adults appear to be protective against early mortality.

Physical work capacity was assessed by bicycle ergometry on 2,779 healthy men younger than 55 years of age. These men were subsequently followed-up for an average of 4.8 years for symptomatic myocardial infarction. Men who were less physically fit than half of their age-matched co-workers were at least twice as likely to experience a heart attack within the subsequent few years. The results are based on a study population consisting exclusively of male fire fighters and law enforcement personnel. Therefore, these results would not be generalizable to the population at large. In summarizing their study, Peters, Cady, Bischoff, Bernstein. and Pike (1983) stated that the results do appear to imply that poor physical fitness is an important risk factor for symptomatic myocardial infarction, especially when conventional risk factors are also present.

Men who are at very high risk for developing coronary heart disease also benefit from being physically active. In the Multiple Risk Factor Intervention Trial (MRFIT), Leon, Connett, Jacobs, and Rauramaa (1987) studied 12,138 middle-aged men who, at entry, were in the upper 10% to 15% of a risk score distribution derived from Framingham Heart Study data. The risk score was based on levels of cigarette smoking, diastolic blood pressure, and serum cholesterol. Leisure-time physical activity status was assessed at baseline. and mortality follow-up was conducted for 8 years. The least-active third of the men had a CHD death rate of 25 per 1,000. The death rates were 15 and 16 per 1,000 for men in the middle and upper-thirds of physical activity, respectively. A significant finding from this study was that a very modest amount of exercise was associated with a reduced risk of dying from CHD. The least-active men expended only 74 kcal/day (15 min) on average in leisure time physical activity. Men In the middle-third of the activity distribution averaged 224 kcal/day (48 min). The men who were most active. 638 kcal/day (134 min). received no additional benefit In terms of reducing CHD deaths despite their much higher levels of activity.

The evidence from recent epidemiological studies that habitual physical activity and moderate levels of physical fitness play an important role In the prevention of coronary heart disease and heart attack In middle-aged adult males is impressive. Although a large-scale, properly controlled clinical trial is probably needed to unequivocally settle this issue. this type of study will perhaps never be done. The inordinate cost of such a study and the high attrition rate associated with exercise are but two of the reasons why this type of study is improbable.

Unfortunately, physical activity does not grant Immunity of coronary atherosclerosis or to an exercise related death. In fact, sudden exertion increases the acute risk of sudden death in persons with coronary disease. What, then, is the risk of dying during exercise? Several recent studies have estimated the risk of death during recreational exercise. Vander. Franklin, and Rubenfire (1982) evaluated the incidence of major cardiovascular complications (CVCs) during recreational activity in a 5 year retrospective survey of fatal and non-fatal CVCs that occurred in community recreation centers during or immediately after exercise. Forty-eight facilities reported 30 non-fatal and 38 fatal CVCs. Although most (57%) occurred during court games and Jogging, the data were insufficient to infer any increased relative risk during these activities. There was one non-fatal and one fatal event every 1,124,200 and 887,526 hours of participation, respectively. These data suggest a small acute risk of CVCs in the general public during recreational activity.

Gibbons, Cooper, Meyer, and Ellison (1980) estimated the acute cardiac risk of strenuous exercise in a large exercise facility. Over a 65-month period, logs of intensity and duration of physical activity were compiled by individual participants at the end of each exercise session. The major types of activity comprising the recorded hours were intensive forms of exercise such as running, tennis, basketball, handball, and racquetball. The male population consisted of 1,934 individuals from 13 to 76 years of age. The median age was 37.8 at the beginning of the study. Most were defined to be healthy after screening via a maximal electrocardiogram. During the time of the study, there were 264,762 man-hours of exercise. Two cardiac events and no deaths occurred. Both men were again exercising regularly at the end of the study. The investigators concluded that there was a small, but not negligible, acute risk of cardiovascular events for adults participating in vigorous exercise who had been given a prior exercise tolerance test.

Exertion-related deaths in an unselected population have been studied in the state of Rhode Island (Ragosta, Crabtree, Sturner, & Thompson, 1984). From January 1, 1975 to May 1, 1982, 81 individuals died during or immediately after recreational exercise. The deaths occurred during a variety of activities, but the majority of deaths occurred during golf (23%), jogging (20%), and swimming (11%). Atherosclerotic coronary heart disease was a presumed cause in 88% of the deaths, primarily in subjects over age 29 with known cardiac abnormalities.

Thompson, Funk, Carleton, and Sturner (1982) reported on 12 men who died during jogging in the state of Rhode Island in 6 years, from 1975 through 1980. The cause of death in 11 was coronary heart disease. The prevalence of Jogging in the Rhode Island population was determined using a random-digit telephone survey. Among men aged 30 to 64 years, 7.4% reported Jogging at least twice a week. The incidence of death during Jogging for men of this age group was one death per year for every 7,620 Joggers, or approximately one death per 396,000 man-hours of Jogging. This rate is seven times the estimated death rate from coronary heart disease during more sedentary activities in Rhode Island and suggests that exercise contributes to sudden death in susceptible persons. However, the occurrence of only one death per 7,620 Joggers per year demonstrates that the risk of exercise is small and suggests that the routine exercise testing of healthy subjects before exercise training is not justified. Thompson et al. (1979) also examined the activity history, medical history, and autopsy results of 18 individuals who died during or immediately after Jogging. The purpose of their investigation was to delineate more clearly the circumstances that may predispose one to death during exercise. Thirteen men died of coronary heart disease and four men and one woman died of other causes. Six coronary heart disease subjects experienced prodromal symptoms but continued vigorous exercise programs. Prodromal symptoms are defined as any change from usual health status and include exertional angina, nausea, unusual fatigue, and abdominal discomfort. The coronary heart disease risk factors for the coronary heart disease cases were not significantly different from those for other age-matched, physically active men.

Siscovick, Weiss, Fletcher, and Lasky (1984) reviewed the deaths of 133 men who were without known prior heart disease but suffered primary cardiac arrest. Cases were classified according to their activity at the time of cardiac arrest and the amount of habitual vigorous physical activity. Among men with low levels of habitual activity, the relative risk of cardiac arrest during exercise was 56. The risk during exercise among men at the highest level of habitual activity was also elevated, but the relative risk was only 5. Relative risk is the incidence of primary cardiac arrest during activity divided by the incidence at other times. Thus, the risk of primary cardiac arrest was temporarily increased during vigorous exercise for all men, but the relative risk was substantially less for men with a high level of habitual activity.

It is apparent that there is a risk associated with physical activity, especially for someone with atherosclerosis and coronary heart disease. However, one may wonder if there is any level of fitness which will protect an individual from an exercise-related death. Could an individual who has the physical capacity to run a marathon be considered immune from coronary heart disease and heart attack? Noakes (1987) studied 36 cases reported worldwide of heart attack or sudden death in marathon runners. The mean age of the runners was 43.8 years (R = 18 to 70) and the mean years running was 6.8 (R = 0.5 to 29). Coronary artery disease was diagnosed in 27 (75%) of the runners. Seventy-one percent of the runners with coronary artery disease had prodromal symptoms, yet continued to train or race. Fifty percent of all cardiac events occurred during or within 24 hours of competitive running events or long training runs. Noakes' review confirmed that coronary atherosclerosis and sudden death do occur in marathon runners. In reality, however, the incidence of such death was low; one to two deaths and a similar number of heart attacks each year in a marathon running population, conservatively estimated at between 18,000 to 25,000 runners. Noakes indicated that three factors would seem to be important in predicting those marathon runners at increased risks of developing coronary artery disease: a strong family history of heart disease, the presence of other coronary risk factors, especially an elevated serum cholesterol level or a low HDL/total cholesterol ratio, and warning symptoms highly suggestive of heart disease.

In conclusion, recent epidemiologic research provides substantial evidence that habitual physical activity and moderate levels of physical fitness lower the incidence of coronary heart disease and heart attack in middle-aged adult males. However, even with these obvious benefits from physical activity. one must also be aware of the risk involved. No amount of physical activity has been shown to provide immunity from progression of coronary atherosclerosis or to an exercise-related death. Indeed, vigorous exertion increases the acute risk of heart attack. However, the research evidence indicates that the benefits of habitual physical activity are much greater than the risk of an exertion-related heart attack.

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By Thad R. Crews

Thad R. Crews is a Professor In the Department of Physical Education at Western Kentucky University in Bowling Green, KY, 42101

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