Physical activity and the prevention of coronary heart disease

PREVENTIVE

MEDICINE

1, 92-120

(1972)

Although the lack of exercise has often been cited as a contributory factor in the development of CHD, until recently little practical advice has been offered. In this paper the authors direct their attention specifically to the role of physical activity in the prevention of coronary artery disease.

Physical Activity of Coronary

and the Prevention Heart Disease’

SAMUEL M.

Fox,

III2

AND

JOHN P. NAUGHTON~ Diuisions George

of Cardiology und Rehabilitation Medicine, Washington University School of Medicine,

Department Washington,

of Medicine D. C. 20037

Data suggest, but fall short of proving, that an increase in habitual physical activity is beneficial. Likely benefits may be as much or more in the area of an improved quality of life as in life extension-quantity. If levels of acceptance of preventive regimens can he categorized as the possible, the prudent, and the proved, there appears sufficient reason to place physical activity as being among the prudent actions to be recommended at present. More studies are urgently needed, particularly concerning whether increased physical activity will contribute to cardiovascular and general health enhancement, increased total human performance and a vigorous creative society. While studies develop better definition, it seems possible with exercise stress testing to “clear” individuals relative to the intensity of exertion that involves an acceptably low hazard of acute cardiac catastrophe yet will provide a predictable improvement in physiologic capability. It appears possible to prescribe the intensity of activity from recently developed information concerning heart rate responses. It is possible also to make useful recommendations as to the type, frequency, and duration of various activities on an individual basis that will fit in with the interests and desired life style of individuals.

That remarkable, (Satchel) Paige has and long life:

seemingly recommended

legendary black the following

Avoid fried meats which angry up the blood. If your stomach disputes you, lie down and pacify Keep the juices flowing by jangling around gently

baseball guidelines

it with cool thoughts. as you move.

1 Supported in part by Grant RT-9 (C-5) f rom the Social and Rehabilitation ment of Health, Education, and Welfare, and the Metropolitan Washington, Medical Program. 2 Professor of Medicine, Division of Cardiology. 3 Professor of Medicine, Director, Division of Rehabilitation Medicine. 92 0

1972 by Academic

Press,

Inc.

player Leroy for a healthy

Service,

Depart-

D. C. Regional

CORONARY

HEART

Go very light on the vices, restful. Avoid running at all times. Don’t look back. Something

such

might

DISEASE

PREVENTION

as carrying

on in society.

be gaining

93

FORUM The

social

rumble

ain’t

on you.

The concept that man is a kinetic animal who thrives best with some activity has been with us since at least the time of Plato. In the Didogues (1) the mode of treatment by which the mind Timaeus tells Socrates, “concerning exercise reduces to order acand body are to be preserved . . . moderate cording to their affinities the particles and affections which are wandering about the body. . . .” Over two thousand years later the question is unanswered as to just how much physical activity is worth the effort; what, in regards to the intensity, duration, frequency, and type of exercise “dose,” produces the optimal “response.” Figure 1 is a conceptual diagram indicating some relationships that may exist, but have yet to be defined, concerning the possible benefits that may result from an increase in habitual physical activity, or indeed, many preventive approaches. One of several sigmoid curves is drawn postulating that initially more input (effort or cost) is required relative to output (yield or benefit) to activate the desired mechanisms. Above this level a lower further input may be necessary relative to further increments of “benefit.” As with many power equations, at high levels a small increment in “benefit” is likely to Individual Maximum \

\

I-

100%

100%

LL L”

k

4 Y

.

DOSE, EFFORT, INPUT or COST FIG. 1. Conceptual diagram from “The Annals of Clinical

relating physical activity to benefits. Research,” Helsinki 3, 404 (1971).

Reproduced

with

permission

94

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NAUGHTON

require a larger relative “cost.” It would be helpful if the activities of daily living, i.e., dressing, shaving, walking to work, lunch, home, etc., were found to place individuals at a position such as A3 in Fig. 1 from which only a modest increase of physical activity (less than the same amount of excess calories above basal) would give a significant increased “benefit” to point B3. It would be even more desirable, but not considered likely, if a “threshhold effect” existed so that once having achieved point A3, only a little extra effort would increase the yield greatly to point B2, as suggested by the dotted line labeled “unlikely curve.” Such a “threshold” may exist for some persons but a specific frequency x duration X intensity “multiple” probably will not define a threshold zone on the curves of many differing individuals. The calculation of such a multiple in terms of MET-Hr/week in excess of the usual ambulatory energy expenditures of less than 3-4 METS4 may be useful for personal record-keeping. Should a specific person walk, jog or run-and who can live long and well without going further than “jangling around gently”? As with the other coronary heart disease (CHD) “risk factors” there is suggestive evidence that correcting physical inactivity is of preventive value, but there is far less data than that which well done research can and will provide. Perhaps we should examine the potential for health enhancement in a larger sense. While there seems to be cause enough to restrict studies to coronary prevention alone, people as individuals and their leadership groups (labor, management, government) might be more convinced of the value of increased physical activity if data were presented in terms of increased total human performance and productivity as well as health conservation. This discu’ssion is restricted to the coronary heart disease problem, in part because of the even greater lack of data on performance and productivity than on CHD. EVIDENCE

FOR

PHYSICAL

ACTIVITY

AS PREVENTION

Morris and colleagues (2) published in 1953 the first persuasive evidence for the protective effect of exercise on the heart; they found that the presumably more active bus conductors in the London Transport System experienced a group incidence of total coronary events, myocardial infarction and coronary deaths less than that of the more .sedentary bus drivers. It is important to recognize that this is an association of less coronary disease with more occupational physical activity and is not necessarily a “cause-and-effect” relationship. Morris in a later paper (3) indicates that there were some selective factors imposed by the company such as a height limitation for conductor applicants and that drivers, on entry into employment, were of greater average girth for a given height than conductors. In 1966 the same group (4) published data indicating that serum lipid and blood pressure elevations appeared to make the greatest contribution to the incidence differences noted, yet they 4 The use of the term METS signifies the multiples of resting (slightly higher than basal) metabolic energy utilization of a given activity. Resting oxygen consumption is approximately 3.5-4.0 ml of oxygen/min for each kg of body weight and one MET is usually taken as 3.5 ml/min/kg.

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could not define whether these factors were influenced by differences in habitual physical activity. In all such observational studies it is difficult to rule out personal and other selection factors that are likely to be operative in respect to the differences in coronary disease noted. This comment in no way diminishes the honor we should accord the epidemiologists who have recognized these limitations. They are, in fact, among the strongest proponents of the “controlled intervention studies” which are now needed to convince an appropriately skeptical scientific community of the power of specific preventive programs. Among the many studies which followed Morris’ pioneer work, the majority found a statistically significant difference or a trend toward the association between increased physical activity of occupation or total life pattern and decreased coronary heart disease frequency in terms of incidence, prevalence, severity, and mortality Table I, assembled by William L. Haskell, is published with his kind permission. With the exception of Chapman’s study (56), the data indicate a lower total CHD experience, mortality, and number of myocardial infarcts in the more active groups. The frequency of angina pectoris is often exceptional, for which no clear-cut explanation is apparent. The optimistic suggestions that the more active persons elicit more angina1 symptoms or that the more active are surviving with angina when, had they been less active, they would be found in columns concerning death or more severe disability, are without statistical support. These studies are covered in greater detail, with some critical discussion of their limitations, in published reviews (5-11). The report of Keys (11) may be excessively harsh, but the criticism is a useful stimulus for the necessary further work. There are some occupational groups in which there is no apparent favorable association and yet no reason to doubt the validity of the observations, indicating no statistically significant difference in the occurrence of CHD (12,13). From many of the studies there is the suggestion, but again with no proof, that the amount of exertion necessary to be protective need not be of such type, intensity, duration, or frequency to prevent its accepted incorporation into the lives of many time-pressured individuals. Taylor’s analysis (14) of railroad occupations placed the amount of excess energy expenditure associated with a considerably lessened occurrence of arteriosclerotic heart disease to be in the order of as little as 500 kcal a day five days a week. Paffenbarger et al. (15) found only a 25% reduction in CHD death rates associated with a 925 kcal/day increase in energy use. The average 70 kg (154 lb) man, who burns I.2 kcal (hereinafter given as Calories) per minute sitting at rest, uses approximately three times that amount (3 METS) walking 2.5 mph, and 5.5 times that (5.5 METS) at a brisk but usually not uncomfortable 3.5.mph. Thus with level walking at 2.5 mph a 154 lb man burns about 144 excess Calories per hour, 324 excess Cal/hr walking at 3.5 mph and 576/hr either by bicycling on the level at 13 mph or running or jogging at 5-6 mph (a rate of 1 mile in 12-10 min) calculated at 9 METS. It is very important that we look at what can be considered a useful minimum that will offer help rather than what

FOX

CORONARY

HEART

DISEASE

.AND

EXPERIENCE

Less Active Group (A)

Subjects”

NAUGHTON

TABLE I ACCORDING

TO LEVEL

More Active Group (B)

Frequency Frequency

Total CHD London Busmen (I) Londoa Postal Workers (I) Los Angeles Civil Service Workers (I) Birmingham, England Men 60-69 (P) North Dakota Residents (I) Kibbutzim Residents In Israel (I) California Mortality Records (P) Med. General Risk

Low General

Risk

Sed. and light Sedentary Sedentary Sedentary Non-farmers No heavy work Sedentary

Mod. and heavy Light Moderate

0.70 0.75

HGWy

FX”l”rS Some heavy Active

work

1.03 0.84 0.39 0.63 0.70 0.18

Angina Pectoris

1.98

in Grdlip in Group

B”

A

Myo-

CHD

cardial Infancts

Mortality

0.53

0.46 0.50

1.40

ACTIVITY

Ref. ASHD MO&lity

2

0.98

1.87

56

0.65 0.47 0.41 0.48 0.33

21 57 0.33

58 59

Sedentary Sedentary Sedentary Sedentary Sedentaly Sedentary

White collar Semi and unskilled Clerks Clerks Clerks

Light Moderate HWY Light Moderate Heavy Outdoor Light and medium Blue collar Prof. and skilled Switchmen Sectionmen Carriers

1.22 0.76 0.71 0.92 0.79 0.46

1.03 0.87 0.82

0.75 0.88 0.78 0.58

60

0.68 0.49

61

(153-0.70

20

0.69 0.58 0.57 0.95 0.75 0.70

62

(I)

Smoked cigarettes 20+ a day Evans County, Men (P)

Conductors

Indoor Sedentary

Chicago Utility Corp. Employees (I)

U.S.A. Railroad Employees (I) Washington, D.C. Postal Employees U.S.A. Men Never smoked regularly

Drivers Sedentary

OF PHYSICAL

Georgia

Male Residents Israel Kibbutzim (I) 40-54 55-64 Farmingham, Mass. Male Residents (I) Men (35-64) Enrolled in HIP of Greater New York (I)

Sedentary Sedentary Sedentary Sedentary Sedentary Sedentary Farm owners Lg. farm owners Prof. managerial No Heavy Work

Light Moderate Heavy Light Moderate HC%Wy

Share croppers Sm. farm owners L&“rWS Full time heavy

0.36 0.37 0.50 0.17

63

64 Sedentary Sedentary Sedentary Least Least

0.34 0.32

AdiVe

0.32 0.22 0.97’

Intermediate Most

0.96 0.90

0.49 0.49

Active Active

n I = Incidence; P = P Prevalence. * A value less than unity indicates a more favorable experience c Angina pectoris and coronary insufficiency. d Total mortality (47% CHD) e Mortality during first 4 weeks following initial MI.

for the more

0.63 0.33 0.40

65

0.27e 0.21

active

16

group.

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gives impressive changes in a brief time -the focus of most past work. Further details concerning activities and their energy cost are included in Appendix II. Among physically relatively inactive workers the questionaire - elicited data of Shapiro et al. (16) and Rose (17,lS) suggests an even lower energy requirement, usually achieved in large part at a low intensity of effort such as is involved in walking. Rose (18) found the following strong association between the prevalence of “ischemic type” ECG findings and the duration of the walk to work each morning taken by 8,948 British male civil servants age 40-64 (excluding men with dyspnea or angina and messengers).

Number of men Percentage with “ischemic type” Mean relative ponderal index

Rose further

electrocardiograms

Duration of walk 0 l-9 389 1.185 6.33 5.14 1.019 0.997

to work 10-19 4.073 4:64 0.994,

(min) 20 3.301 4:18 0.990

states:

The association could not be accounted for in terms of differences in age, smoking habit, grade of employment, blood pressure, serum cholesterol, or glucose tolerance; those who walked less tended to be a little more overweight. It remains to be seen whether the duration of the walk to work is merely an indicator of some other etiological characteristic (e.g., a generally greater level of physical activity). Alternatively it would be encouraging if further studies were to show that as little as 20 minutes walking each day might help to protect a man from CHD. A controlled trial will be needed to test this hypothesis.

From a further analysis (19) of Zukel’s North Dakota study it is apparent that those who were vigorously active for more than one .hour a day had less than one-fifth the CHD incidence of those involved for less than an hour. The data do not permit an analysis of briefer activity periods. Kahn, in his study (20) of Washington, D.C. postal workers, became convinced that recent activity is more important than that which was previously habitual but discontinued in the past. It appears one cannot count on carrying long-term “credit-in-the-bank” from school or college activities. Although it is likely that less benefit may be obtained for the same effort in the later decades of life, the inference of the study of Brown et al., (21) on men over age 65 suggests a persistent favorable influence of lifetime patterns even after retirement. Unfortunately there are no data on women, but no one has demonstrated a reason why preventive benefits should not accrue to those who are physically active as much as they may for men. Morris and Crawford (22) analyzed the reports of gross postmortem examinations of 3800 presumably noncoronary deaths and found that there were fewer large fibrous myocardial patches, small multiple scars, large healed infarcts and coronary occlusions in the hearts of those of more active lifetime occupation than in the hearts of those more sedentary. Within the coronary arteries, however, the difference in the degree of severe atheromatous deposition was not as great although deposition was slightly less prominent in those of moderate activity. Spain and Bradess (23) found the same lack of difference

98

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in their study in the U.S. It may be that the hearts of those conditioned higher energy expenditures will adapt by developing larger arteries likely to be compromised by a given amount of atheromatous deposition, this hopeful hypothesis has available neither convincing supportive opposite data. POSSIBLE

MECHANISMS

OF

PREVENTIVE

by less but nor

BENEFIT

Table II indicates mechanisms by which an increase in habitual physical activity may reduce the occurrence or severity of CHD. It must be stressed that the available data are inadequate or inconclusive on most all points relative to middle-aged persons in developed countries. Development of collateral passages around coronary constrictions have been reported in experimental animal work and it has been clearly established by arteriography that some middle-aged persons with coronary obstructions do possess interarterial collateralization. Although well-designed studies of post-infarct patients trained for periods of less than a year have not shown these desired changes frequently, the interval of training between coronary angiograms may have been too brief or the beneficial changes may have been significant but in vessels too small for adequate visualization. Perhaps visible change cannot be expected in vessels already badly compromised and thus unable to respond to the stimulus of the increased myocardial demands of exertion. Encouraging reports of peripheral vascular improvement on exercise programs suggest improvement can occur even late in the course of atherosclerotic disease (24).

TABLE II MECHANISMS BY WHICH PHYSICAL MAY REDUCE THE OCCURRENCE SEVERITY OF CHD Physical Coronary Vessel size Myocardial efficiency Efficiency of peripheral blood distribution and return

Arterial

may: Decrease Serum lipid levels triglycerides cholesterol Glucose intolerance

Increase collateral vascularization

Fibrinolytic

activity

ACTIVITY OR

Platelet

stickiness

Arterial

blood

capability oxygen

Heart Red-blood-cell

mass

and .blood

rate

volume Vulnerability

Tolerance

pressure

content

to dysrhythmias

to stress Neurohonnonal

Prudent loie

living

de vivre

overreaction

habits “Strain” associated “stress”

with

psychic

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Although work in young animals suggests that physical training will increase coronary vessel size we have no controlled studies in humans. The interesting report by Currens and White (25) of large coronary vessels found at post-mortem in the famous marathon runner DeMar may only mean that he succeeded with a superior endowment. That these vessels can become larger, and therefore less compromised by atheromatous deposits, must remain conjecture. Myocardial efficiencygreater work performed at lower cost- is suggested by some data (26), particularly that in which an increased stroke volume and a slower heart rate at a given work load occurs after training, but efficiency in intact man is hard to assess. The apparent reconditioning of the mechanisms controlling peripheral blood distribution and return and, perhaps, a slightly increased blood volume might act more through preventing secondary complications (hemorrhagic or hypotensive shock with inadequate venous return, etc.) after an accident or infarct than prevent damage primarily (thrombosis and/or electrical failure). Recent studies on blood changes with physical activity indicate greater arterial oxygen content (26), suggest a brief enhancement of fibrinolytic activity (27) and decreased tendency for platelet aggregation (28) without accelerated coagulability, but no long-term benefits have been documented. Depending on the importance one accords to the psychological aspects of CHD there is a varying potential for benefit resulting from improvement in personal self-image, “joie de vivre” and tolerance to stress that is reported by many- but not all- who invest their energies in an endurance-enhancing activity program (29,30). Physical exertion also still appears to be a highly desirable tranquilizer for most everyone. The late, beloved Howard Sprague often said, “You see no charwomen troubled with insomnia.” Although weight-lifting and isometrics may do little for cardiovascular disease risk reduction, such activities may have a place in building self esteem. In today’s stressful world reenforcing “self-image” may be important as a means of promoting health related efforts. Considerable care must be taken, however, to avoid the taxing pressor responses that often accompany straining against significant resistance (31). It is important to emphasize that with some arm-shoulder-trunk exercises there is an associated, potentially dangerous increase in blood pressure and heart rate greater than that found with endurance-enhancing exercises of similar oxygen demand (32). There has been hope that a major reduction in serum lipid levels and obesity might be achieved by increased habitual physical activity. Although reports show varying degrees of favorable response, most of them are of modest proportions at best. Lipid levels may not be adequate indices of more subtle metabolic benefits but the burden of proof clearly rests on the proponents. With a few exceptions cholesterol lowering appears correlated more with reduction in weight than to the increase in calories expended above levels of sedentary living. Tooshi (33) recently reported that middle-aged men who walked, jogged, and ran for 15 min a day had an improvement in fitness; those exercising 30 min a day improved body composition as well (more

100

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muscle, less fat for a given weight); but a significant change in cholesterol was found only in the group exercising at the same intensity for 45 min a day five days a week. Triglyceride levels usually fall significantly but briefly (reduced for 24-48 hr after moderately severe exertion); however, less is established about their relevance to CHD risk reduction (34). We do not know if the more physically active person can get away with eating more saturated fats than the less active or indulge in other dietary excesses beyond the extra calories his activity uses. Elevated blood pressure as a CHD risk factor and its reduction as a means for. preventing CHD is discussed elsewhere in this Forum. Some studies report patients whose moderately elevated pressures at rest have come down during a physical conditioning program (35) but this has not been a significant or major feature in most controlled studies. Boyer and Kasch report considerable improvement in a recent report (36). What perhaps is more important than the usually obtained resting blood pressure is the “operational blood pressure” with which we live, work, and love. Exercise stress test results suggest these operational pressures are likely to be significantly reduced but studies of real life blood pressure responses are needed. Following endurance stimulating physical training there is usually a reduction of heart rate at rest and more impressively so at various levels of submaximal exertion. The mechanisms producing the training bradycardia are not defined but this effect appears to be a reliable indicator of cardiovascular adaptation of a desirable type. Bradycardia and lesser blood pressure (and the pulse-pressure-product calculated from their multiplication) may be the major contributors to the markedly increased tolerance to and capacity for exertion after physical training in most patients with angina pectoris (37). As yet data is too meager on whether conditioning protects the heart against further damage or permits a person thereby to survive after a further insult. Neurohormonal influences, including those relating to lipid-carbohydrate metabolism, tend to change in a way that can be considered salutory, but such changes are not yet proven to reduce CHD risk. If catechol responses to both physical and psychic stress can be made more appropriate this might have significance in the “over-pressured” lives to which the coronary prone may expose themselves. There is a suggestion (16) that sudden death may be less frequent among those habitually more active, particularly among men under age 65. A lessened incidence of cardiac dysrhythmia or decreased vulnerability to such disturbances is postulated, but too little data is available. Sudden death was not decreased in one otherwise encouraging diet intervention study among survivors of myocardial infarction (38); this represents a specific reason for accelerating the definitive evaluation of the contribution of physical activity among the multiple factors that may effect CHD risk. These possibilities command the attention of investigators who will need to improve measurement techniques as well as conduct properly controlled studies. therefore, from epidemiologic and other There is suggestive evidence, studies that early onset, severity, and death from CHD may be delayed or less-

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ened by increases in habitual physical activity. One can present numerous, but as yet unproven, mechanisms by which such benefits might be produced. PRESCRIPTION

OF PHYSICAL

ACTIVITY

If individuals, the community, and government accept as persuasive the apparent psychologic, physiologic, and preventive benefits to be derived from habitual physical activity, it is important to determine the manner in which such increased activity can be safely undertaken and maintained at a level of meaningful personal reward. Without enhancing health and feelings of pleasure or accomplishment the “drop-out rate” from activity programs can be, and in some trials has been, discouragingly high (29,30). Hellerstein and associates (39) have had high adherence rates within a pleasant and competently staffed setting which is not too difficult to reproduce in many other communities. Individuals interested in becoming more active are well advised to obtain a “clearance” from their physicians or, with their referral, to obtain such an evaluation from those who have special competence in assessing the risks of overstressing physiological reserves with significant exertional increases. The American Medical Association, the American Heart Association, and the Council on Rehabilitation of the International Society of Cardiology are developing guidelines for exercise testing. Appendix I gives some precautions that have been discussed in these groups and some notes on how differing test modalities (steps, bicycle ergometers, treadmills) can give comparable results. Even persons with severe disease can often benefit from a carefully prescribed activity program, but the required individualization of assessment and recommendation for those with disease cannot be encompassed by this report. For any person the type of activity, frequency, duration, and intensity should be defined in the formulation of the prescription.

Zntensity A multistage exercise test offers the most practical approach to assessing the appropriate intensity of exertion- usually the most difficult element in the prescription. A carefully monitored session of the actual program contemplated would often be preferable were it not for the impracticality of trying to provide this for large numbers of subjects with many differing interests. The determination of self-limited or physician-limited maximum capability as recommended by Bruce and associates (40) provides data of great value but it is our opinion one can obtain sufficiently useful information by stopping exertion when the heart rate reaches from 80-90% of the age-predicted maximum (41,42). The “target heart rates” recommended in Scandinavia and endorsed at the Myrtle Beach Conference (41) (Fig. 2) are at or just under these levels and are suggested as standard goals if no contraindications to continued testing develop. (See Appendix I for signs of intolerance to exertion.)

In no case should a subject

be permitted

or encouraged

to press on to any

102

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r

.’ .I I I T 0f Ii 150

I 140

130

X

# 0 0 A + 0

Robinson Astrand. et al. Astrand Bruce Binkhorst Anderson Lester, et al.

A Kasch d al n Saltin & Grunby # Hollman 8 Knipping

140

t

I

I

I

I

I

I

I

I

I

Ll

25

30

35

40

45

50

55

60

65

FIG.

2. Decrease

in maximum

ACE IYears) heart rate with

age for healthy

men.

such arbitrary levels if signs or symptoms suggest significant problems. The testing should preferably be done using three or four relatively modest increments of exertion with each stage lasting three or more minutes. Figure 2 presents data from studies of North American and European males under varying conditions and with differing criteria for what was considered acceptably close to “Maximum.” The vertical bracketing bars indicate the spread of one standard deviation. The numbered horizontal lines indicate the “Scandinavian-Myrtle Beach Heart Rate Criteria” for each decade. It may be appreciated that no single line will adequately represent the data of the apparent decline of maximal heart rate with age. The formula “Maximum Heart Rate = 220 - Age in Years ” defines a line not far from many data points but is clearly lower than the data of Lester, reviewed recently by Sheffield (52). Apparently the heart rate for a given submaximal workload does not have a corresponding decline with age among those who maintain a high level of fitness, but the data base for this impression needs expansion. After finding that a person can comfortably undertake exertion at a certain heart rate without evidence of impending or actual dysfunction it is possible

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to teach him to measure his pulse rate and use it as a guide to determine his activity intensity. In symptomatic subjects the appearance or characteristics of chest discomfort or angina1 pain may be a better guide, as may be dyspnea or the rapid onset of fatigue. It appears reasonable to advise an otherwise presumably healthy person (who may have some CHD risk factors) to begin his activity program at a level that increases his pulse rate to no closer than lo-15 beats (“Heart Rate stress-test level at which he had no impendMargin”) below the “clearance” ing or actual dysfunction or complaints. Thus if a 52-year-old man comfortably achieved the Scandinavian-Myrtle Beach Heart Rate Criterion (S-MBHR criterion) of 140 beats/min it has been found useful to encourage such a person to undertake peak initial intensities at a pulse of 125-130 after an appropriate warm-up. Such exertion will usually require about 60% of his predicted maximal oxygen capacity (“Aerobic Power”) (Fig. 3) and will usually produce perspiration, an increase in breathing, and a not unpleasant brief sense of fatigue; all of which seem desirable. Figure 3 presents data from Robinson’s early treadmill studies and Astrand’s experience using bicycle ergometry illustrating the almost linear relationship of submaximal oxygen consumption, expressed as percent of maximal, and simultaneously measured heart rate, as percent of maximal, in men of various ages in the United States and Sweden. From this it can be demonstrated (by the dotted lines) that a 70%-of-maximum heart rate effort is likely to be accompanied by a 55-60% of maximum oxygen utilization. An 85%-of-maximum heart rate intensity of exertion is likely to evoke a 75-80% of aerobic capacity response. Where an individual’s maximum heart rate has not been determined by actual observations it is considered acceptable to use similar calculations from predicted maximum oxygen capacity as in Fig. 4.

lCO-

600” >

50.

3

40.

s

30-

_--

__

---_-

20loOo

10

20

30

40I

l /.

MAX.

FIG. 3. Oxygen consumption and measured from a diagram by Taylor et al. (53).]

50*

60I

HEART

heart

-gj:ij 70I8

:: ‘Y.--g adI,, I 90 loo ,

RATE

rate in American

and Swedish

men.

[Adapted

104

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WORK LOAD

362 presumably healthy man 44 yaars avarage age Saaaelor.et al .AM.Ht.J. RS-T Sepmont Displacemrnt

%&dt:ip~es ;‘::::r>*L!7!’

aftb$tg

Motabalic

mi!‘i’vo’ts

Rata (1 MET=approx.3.5 ml*“z/ z

FIG. 4. Progressive multistage exercise test relating heart rate, blood pressure and physical work load. The broken lines indicate the upper and lower limits of 1 SD of the heart rate (measured at the 3rd min of load) of 362 presumably healthy men, average age 44 yr. [From !?pangler et al., Amer. Heart J. 80,755 (1970).]

Figure 4 graphically illustrates heart rate response (and can also include blood pressure) to exertion from numerous differing modes of exercise, as indicated in Tables IV and V. The work load can be represented by its metabolic requirement in milliliters of oxygen per minute per kilogram of body weight-or in METS. Thus the representative heart rate response (usually during the third minute or later in an exercise stage) should permit a graphic comparison to other experience such as that of Spangler et al. (42). A line plotting the heart rate increase with exertion should be approximately below the upper of the two limit lines for “fit” men less than 50 years of age. Those in better than “average” condition will lie near or below and to the right of the lower limit line, having fewer heart beats for a given oxygen requirement (and having a larger “oxygen pulse index” calculated as ml OJmin/kg per heart beat.) A heart rate rise above S-10 beats/min/MET of increased exertion suggests dysfunction and/or a deconditioned state. The line for such an assessment should be made from two or more heart rate points above 122 beats/min to minimize psychic influences. Extension of such a line to the level of predicted heart rate for age Gill permit a crude estimate of predicted maximum oxygen consumption or MJ3Tlmaximum for an individual but such a calculation is neither accurate nor very useful in the prescription of a physical activity program. Symptom reports and heart rate responses during or just after exertion appear more useful indices for adjusting the activity prescription.

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Individuals who have had a favorable recovery from myocardial infarction and are interested in avoiding disability and recurrences should not undertake high levels of exertion for at least three months, probably longer, due to the possible added stimulus to ventricular aneurysmal dilatation and dysrhythmias. ‘For such persons, after three or more months, it appears useful to use an intensity prescription with a heart rate margin 20 or more beats below that achieved without difficulty during a multistage progressive exercise stress test. New exericse and monitoring devices are becoming available that are specifically built to facilitate the “heart rate prescription” approach. Even though the S-MBHR criteria are above the level at which psychic stimuli to tachycardia usually make much of a contribution, previous “clearance” for exertion just under these levels does not mean a person should feel “cleared” to push to these levels when under any severe psychic stress. Anecdotes, rather than more scientific appraisals, suggest that psychic stress may predispose to catastrophies perhaps through an elevated catecholamine-sympathetic nervous system milieu. When starting exertion it is of great importance to work up through a gradual “warm-up” of 2-4 min or more; the longer time being appropriate for the older, the less well conditioned, and for those who wish to move promptly to high levels of activity’as may occur in competitive games. It is also important to caution subjects against using clothing that blocks body surface cooling through perspiration as they predispose to heat stroke or heat exhaustion. The weight loss that accomfianies the use of such garments is of no value as it should be promptly regained by proper fluid and electrolyte replacement. Interval training techniques using brief periods of relatively high level activity followed by lower levels permitting partial payment of oxygen debt may have advantages for competitive athletes but high intensity appears to be the component most likely to evoke cardiac problems. There is some evidence (44) in young men that endurance capacity is not further augmented by high intensity interval training as compared to results achieved by the same duration and mean level of exertion without such peaks. Similar work in older persons is needed, but such high intensity intervals of training are not recommended. Duration There is inadequate definition of the benefits achieved relative to cost in time, effort, and resources for all components of the activity prescription (Fig. 1) including frequency and duration. In the time-pressured circumstances to which many expose themselves it is hoped that a safe and interesting increase in intensity will permit a shortening of duration to periods that do not excessively disrupt life patterns. Many persons express more concern about the demands of time getting to and from the site of interesting physical activities than that involved in the exercise itself. Durations less than those which produce perspiration may not provide an apparently desirable stimulus for peripheral circulatory adaptation that may

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help persons contend with stresses in addition to those of high environmental temperatures themselves. At a comfortable temperature, exertion for eight minutes will usually produce a cutaneous vasodilatation and early perspiration. Many persons would rather exercise less frequently for longer than 8-12 min to save total weekly travel and shower time but the relative values of frequency-intensity-duration components have not been defined. Much depends on whether one jogs around one’s home, uses a stationary bicycle or feels that a less frequent game of tennis, squash, or handball is most satisfying. In the present state of inadequate knowledge a quarter-hour of relatively high intensity exertion (using the appropriate “heart rate margin”) can be considered a desirable minimum. Such activity should always be preceded by an adequate warm-up and followed by a cooling down phase of lessened activity before a shower. The shower should be neither unusually hot nor cold. A sauna or steam bath is probably hazardous for some although too little data is available. Frequency Increases in physical work capacity and feelings of well-being have been achieved by previously sedentary American men participating twice a week in structured exercise programs lasting approximately one-half hour at an intensity of about 70% of age adjusted predicted maximum heart rate (30) (about 60% of maximum aerobic capacity Fig. 3). More benefit and a more rapid rise to a satisfying level of performance was achieved with three active periods per week of equivalent intensity and duration. Some individuals became more active outside the structured program with pleasant weekend activities that appeared to provide further improvement. Siegel, Blomqvist and Mitchell present some important data and a concise relevant review (45). Thus a reasonable state of improved capacity for work and pleasure can be achieved by a program three times a week. This level can often be maintained by twice-a-week activity but many persons report a sense of lack if they don’t exercise every other day. More information is needed on larger numbers of subjects including all ages and both sexes. Type of Activity Activities stimulating enhanced endurance capacity seem definitely superior to strength-building exercises for improving the quality of life, but as with other elements, we have little information relative to life extension-the quantity of life. It seems important to warn persons of the potential hazards of blocking blood flow through the lungs by straining with a closed glottis-as may contribute to the snow shovelling catastrophies reported. For some people there is a desire for some degree of competition, but other individuals find this distinctly undesirable. Some prefer jogging by themselves or riding a regular or stationary bicycle. There are numerous reports that many persons enjoy group programs with the camaraderie that is often found in them. Unfortunately there is a great lack

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of facilities for different activities within reasonable access for most of our citizens (distance and/or cost of transportation, parking and shower facilities as well as activity areas). There is also much that needs to be developed in the area of new rules or modifications of games to increase interest, reduce unwanted competitive elements and involve more persons per hour or day at reasonable expense. It is a challenge to our community planners, medical societies, Regional Medical Programs, academic institutions and other elements of our complex society to develop the appropriate means for helping individuals find rewarding activity. One author (SMF) personally favors games such as tennis because of the satisfaction of the too infrequent but satisfying well hit shot, but there is little question that a run-jog-walk program can take less time and special facilities than most other activities that produce improved performance. Badminton should have a renaissance similar to what has occurred in tennis, and is much less demanding of facilities and funds. Skiing, skating, bicycling, canoeing, and vigorous dancing all have apparent benefits and may sustain interest for hours. Cross-country skiing has become much more popular recently in many parts of the United States and Canada although we do not have the well-marked trails illuminated at night such as are found in Oslo, Stockholm and Helsinki. Caldwell’s small book (46) is an excellent introduction to this relatively inexpensive and pleasant form of winter activity. Ski touring can be a fine snowseason substitute for a walk-jog-run program and is less demanding technically for the middle-aged novice than is downhill skiing, to which it can provide a partial introduction. With the upsurge of concern about pollution and overcrowding of cities -of our air, of our parking facilities, etc., there is an encouraging trend to try to make bicycle riding safer and more acceptable. A rather comprehensive text (47) h as h e lp e d many with only a casual interest in bicycling with their families on weekends become hobbyists capable of keeping a IO-speed bike in top condition for commuting to work or for country touring. Calisthenics used to seem to us relatively unrewarding, but time and its effects have convinced us that flexibility exercises and calisthenics during a warm-up have much to recommend them. By calisthenics we mean head, neck, torso and hip bending (flexion and extension) maneuvers with or without use of the arms. There is a sufficient number of anecdotes of back problems attributed to straight leg “bending to touch the floor” flexion exercises and also the “head-neck and leg elevation from a prone position on the floor” extension exercises that we believe both of these should be done with caution if at all. Push-ups, squat-jumps and related body weight lifting exercises are not included in our use of the term “calisthenics” and must be undertaken with due regard for the greater energy, muscle, and joint demands required by them. A relative value scale or listing of activity “virtues” based on representative groups of both sexes at differing age groups does not exist even for end points of physiologic improvement. Appendix II includes some data and references that may be of assistance. The determination of that which

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produces greatest psychologic, socioeconomic and epidemiologic (preventive) end points will be more difficult, but in our opinion will be well worth the required research effort and expense. While this information is being developed it appears appropriate to place emphasis on what activities are rewarding, pleasant, and preferably fun for the individual and are feasible within the strictures of his life circumstances. These appear more important than placing emphasis chiefly on that which is most efficient in achieving physiologic improvement. It is quite possible that the physical activity itself is more important than the fitness achieved. We may be confounded by the early coronary death of a former athletic “great” who might have retained his exercise test capabilities at a better than average level because he was a constitutionally superior individual, yet he may have lost out by not maintaining an active life. This conjectural concept needs more definitive data, but we wish to emphasize the habitual physical activity rather than the results of fitness testing. From the socioeconomic standpoint it is important to society to increase the quality and perhaps the productivity of a person rather than merely extending his life into the years when other infirmities are more likely. It has been calculated (48) that for the “average” 35-year-old white man in the U. S. a reduction by one-half in cardiovascular-renal deaths thereafter would result in a 4-year delay of his expected time of death from age 73.5 yr to 77.5. It seems relevant to suggest that men of around 35 years of age, pausing to assess the meaning of life and their options, will find greater persuasion to undertake more prudent living if they feel they will be adding more “life to years” as well as “years to life.” Hellerstein and colleagues (49) have made some longoverdue observations on enhanced sexual capability and activity after physical training that seem highly relevant. Thus there is an ever-increasing body of knowledge suggestingbut unfortunately falling short of provingthat increased habitual physical activity can be useful in enhancing health, improving the quality of life and probably contributing to the prevention of coronary heart disease for many if not most persons. Because of the widespread renewed interest, and at times even hazardious or imprudent involvement of people in unaccustomed physical exertion, it is imperative that research and training efforts be supported which will provide greater professional competence in evaluating and “clearing” individuals and large groups of our citizens for the best forms of new, interesting and rewarding activities. The widespread involvement by members of our population warrants an urgent and accelerated research effort to define those activities and program prescriptions which are most useful in the cause of coronary heart disease prevention. APPENDIX

I

Procedures for the “clearance” of presumably healthy middle-aged individuals who wish to undertake strenuous new physical activity after having been relatively sedentary for some years: Clearance evaluations allied health personnel,

should be done by physicians, cognizant of the circumstances

often greatly aided by involved-including

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the sore joints and other musculoskeletal problems often elicited by new activities. Particularly, the increased cardiorespiratory demands and potential hazards of strenuous new activities should be understood by the “clearance” evaluation team. Although physicians may find this type of work fascinating and of great value in their relationship with their patients it may be more appropriate for many communities to set up a referral facility for the evaluation of such subjects and also to help the practicing physicians handle many aspects of CHD risk reduction including the exercise prescription, i.e., support of the physician’s prescription for control of diet, smoking, and blood pressure. The evaluation should include a review of the history of the person and his/her family for the occurrence of heart disease and coronary risk factors. The assessment of discomfort in the chest suggestive of angina and palpitations and dysrhythmia is particularly significant. The review of systems, physical examination, and resting electrocardiogram are also important as a safeguard against inappropriate exertion for those who have latent or subclinical disease. Table III lists some contraindications and causes for special care. Under III.6 in Table III, “Clinically severe hypertension” we are hard put to draw more precise guidelines. Conceptually it is hazardous to push a person into any situation, emotional or exertional, in which his blood pressure (presumably the systolic being the best indicator) is likely to rupture a vessel or elevate an atherosclerotic plaque into a position productive of vascular occlusion. Such events appear to be quite infrequent even in the atherosclerosis-thrombosis-prone older person. We know of no data that permit better guidelines than relying on well-reasoned clinical judgment. We believe, however, that many time-pressured, energetic, and moderately hypertensive persons will find a physical activity program worthwhile and this justifies cautious testing and activity prescription for them. An exercise test designed to assess the body’s responses to exertion is of great importance, but does not reduce the importance of the aforementioned inquiry, particularly a perceptive review of symptoms. Exercise testing can help reveal some, but not all, latent coronary disease of significance, aid in particular the prescription of the intensity of the activity to be performed and help in motivating and maintaining the adherence of individuals by providing an objective measure of change or lack of change in status. A multistage procedure can use steps, a bicycle ergometer, or a motordriven treadmill, as the means of eliciting a specific amount of work in a given period of time. This application of power can be calculated and expressed in absolute terms such as the predicted number of milliliters of oxygen (total, or in excess of resting body requirements) or probable multiples of the resting oxygen requirement for performing the prescribed activity. The latter units of reference have been called “METS” and indicate the figure by which the probably exertional oxygen requirement per minute would have to be divided to give 3.5 ml OJminlkg of body weight-the standard usually given for 1 MET or the resting oxygen requirement. The practicing physician may find it economically unrewarding to undertake exercise stress testing in his office with the requirement more frequently

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CONTRAINDICATIONS I. Absolute

III.

NAUGHTON

TABLE III TO EXERCISE AND

EXERCISE

TESTING

Contraindications

1. 2. 3. 4. 5. 6. 7. 8. 9.

II.

AND

Manifest circulatory insufficiency Acute myocardial infarction Active myocarditis Rapidly increasing angina pectoris Recent embolism, either systemic Dissecting aneurysm Acute infectious diseases Thromhophlebitis Ventricular tachycardia and other (multifocal ventricular activity) 10. Severe aortic stenosis Relative Contraindications”

(“Congestive

Heart

Failure”)

or pulmonary

dangerous

dysrhythmias

1. Uncontrolled or high-rate supraventricular dysrhythmias 2. Repetitive or frequent ventricular ectopic activity 3. Untreated severe systematic or pulmonary hypertension 4. Ventricular aneurysm 5. Moderate aortic stenosis 6. Uncontrolled metabolic diseases (diabetes, thyrotoxicosis, myxedema) 7. Severe myocardial obstructive syndromes (suhaortic stenosis) 8. Marked cardiac enlargement 9. Toxemias of pregnancy Conditions requiring special consideration and/or precautions I. Conduction disturbances a) Complete atrioventricular block, h) Left bundle branch block, c) Wolff-Parkinson-White syndrome 2. Fixed rate pacemakers 3. Controlled dysrhythmias 4. Electrolyte disturbances 5. Certain medications a) Digitalis, h) p-blocking and drugs of related action 6. Clinically severe hypertension (Diastolic > 110, Grade III retinopathy) 7. Angina pectoris and other manifestations of coronary insufficiency 8. Cyanotic heart disease 9. Intermittent or fixed right-to-left shunts 10. Severe anemia 11. Marked obesity 12. Renal, hepatic and other metabolic insufficiency 13. Overt psychoneurotic disturbances requiring therapy 14. Neuromuscular, musculoskeletal and arthritic disorders which would

(1 In the practice of medicine relative contraindications.

the value

of testing

often

exceeds

prevent

the risk in patients

activity. with

these

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being stated that a defibrillator and trained associates are mandatory. If one wishes to undertake multistage exercise testing, however, it can be done with single steps which can be fitted within each other for storage. With boxes of 4, 8,16, and 24 cm in height it is possible to build additional single step heights of 12, 20, 32, and 40 cm for a series of progressive stages chosen from those listed at the top of Table IV. Step tests are more likely to produce ECG artifacts from electrode and cable movement than with other modes of measured exertion, due to body motion. New developments and pricing of appropriate bicycle ergometers and small treadmills make them increasingly competitive for a small testing facility. Table IV provides some schedules whereby increasing workloads of predictable oxygen requirements can be applied by use of steps or a motor driven treadmill. Although an excellent World Health Organization handbook (54) suggests varying the rate of ascents of a set of steps to impose increasing work loads we find subjects often have difficulty getting the desired speed without experiencing an increased heart rate from anxiety and we therefore prefer using the same cadence over steps of differing height. These can be built at modest cost as indicated in a useful booklet available from the Tennessee Heart Association (55). TABLE

IV

APPROXIMATE COMPARABILITY OF ENERGY REQUIREMENTS OF SOME STEP TESI AND TREADMILL PROTOCOLS FOR ADULTS [REPRODUCED WITH PERMISSION FROM “THE ANNALS OF CLINICAL RESEARCH," HELSINKI 3, 404 (1971)l STEPS cm HEIGHT METS Ellertad

= VI LyI-

. .:.::.Lji ::./.: /,>,/ &?!~;I

10

PER CENT

3.4

MILES

GRADE

I

Bruce

Balks : -NI ~1 Galke u. wLe I- Nauohtan

PER HOUR

METS MI.GI/Kg/mia CLINICAL STATUS

IV

III

II

I

and

NORMA

1 I

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A motor-driven treadmill with varying grade (rise of ramp over horizontal distance travelled) and speed sets the pace for the subject but involves more expense, electric power, noise and physical space than either steps or bicycle ergometers. For a laboratory with a heavy work load a treadmill apfiears justified, however. A warm-up trial before the actual test is helpful in familiarizing the subject with the steps or treadmill and particularly the rate of activity required. It is best to obtain three assessments of work load response eliciting a heart rate of 122 beatslmin or over if a figure for predicted maximum rate is to be calculated. Many individuals have difficulty walking faster than 3.0,3.4; or at most 4.0 mph, particularly up a grade. We recommend that the rate be such that jogging or running is not necessary, particularly if calculations, of probable oxygen utilization are to be made rather than actual measurements. Efficiency varies to a much greater extent with jogging and running than with. walking. More details on testing can be found in a recent review (53). Table V gives the same type information for a bicycle ergometer with’s tabular,adjustment for body weight. Bicycle ergometers take up little space, are not very noisy and permit good electrocardiographic and blood pressure recording. The desired frequent calibration of electrically braked units may not be easy to arrange for and thus the less expensive. friction-brake units may be preferable even though the revolutions or distance per minute must be exactly recorded. As bicycling comes back into popularity in America there should be less quadriceps femoris muscle fatigue which has, in some cases, limited the ability to evaluate high level cardiovascular performance. The table gives the work load in both kilogram meters per minute (frictionbrake) and watts (electric) with the approximate oxygen and kilocalorie costs TABLE

V

OXYGEN REQUIREMENTS OF BICYCLE ERGOMETRIC WORK LOADS Workload kgmlmin watts (approx.) Oxygen Used Including Basal ml/min (approx.) kcallmin bpprox.) Oxygen Used mllminikg of body weight for: Ihs kg 88 40 110 50 132 60 154 70 176 80 198 90 220 100 242 110 264 120 kgmimin Work Load

150 25

300 50

450 75

600 100

750 125

900 150

1050 175

1200 200

1500 250

1800 300

600

900

1200

1500

1800

2100

2400

2700

3300

3900

3

4.5

6

7.5

9

10.5

12

14

17

20

15 12 10 8.5 7.5 6.67 6 5.5 5

22.5 18 15 13 11 10 9 8 7.5

30 24 20 17 15 13.33 12 11 10

37.5 30 25 21.5 19 16.67 15 13.5 12.5

45 36 30 25.5 22.5 20 18 16.5 15

52.5 42 35 30 26 23.33 21 19 17.5

60 48 40 34.5 30 26.67 24 22 20

67.5 54 45 38.5 34 30 27 24.5 22.5

82.5 66 55 47 41 36.67 33 30 27.5

97.5 78 65 55.5 49 43.33 39 35.5 32.5

150

300

450

600

750

900

1050

1200

1500

1800

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per minute for persons who can produce these work loads without having to exert themselves maximally. A conversion factor of 5 kcal/liter 0, consumed is used although something in the range of 4.8 might be more exact. The bottom section converts the oxygen costs into milliliters per minute per kilogram for various ranges of body weight from 40-120 kg. This indicates that a heavier person should be able to apply more power (work per unit time) than a lighter person if he is in the same relative fitness status for his weight. A conversion to METS may be obtained by dividing the oxygen used in ml/min/kg of body weight by 3.5 (equal to one MET or the average resting oxygen consumption). Most patients with symptomatic angina pectoris find it unusual to be able to exceed 8-10 METS without eliciting discomfort or pain or S-T changes in the electrocardiogram unless prior symptoms occurred with dysrhythmias or only with very strenuous exertion. The test can be given with no rest pauses between stages or with 2-6 min interruptions to permit a major recovery and payment of oxygen debt before starting another and usually more severe level of exertion. After such a rest pause the duration of the next phase may also have to be somewhat longer to permit a fairly reliable assessment of the response of the body to that work load. Although six minutes of submaximal exertion permits a “near steady” physiologic state, it is usually sufficient to record the heart rate, the electrocardiogram and systolic blood pressure during the fourth minute of exertion and often during the third minute. An extended and continuous test such as a four stage’ test of six minutes per stage may produce general fatigue and thereby may not permit a valid relationship between load and cardiovascular response to be established. A fourstage test with three to four minutes at each stage eliciting signs or symptoms of poor exercise tolerance or a heart rate to or exceeding the ScandinavianMyrtle Beach Heart Rate Criteria (vi& in@a) is suggested as representing a reasonable clearance procedure. The increase in work load of each stage should not exceed 1 MET (3.5 ml O,/min/kg of body weight) for each minute of the stage’s duration, i.e., 3 METS or about 10 ml OJmin/kg for a stage of 3 min duration. If a person intends to expose himself to maximal or near-maximal exertion it appears logical to have him or her push up to or into a level of severe fatigue or exhaustion. Only by having the subject exceed the likely intensity and a realistic equivalent of the duration of contemplated exertion can the physician be reasonably assured that “clearance” for such exertion is justified (41). The age-adjusted “target” heart rates recommended for an initial “clearance” evaluation are as follows and conform to reports from Scandinavia (43) and the Myrtle Beach Conference (41). Age (years) 20-29 30-39 40-49 50-59 60-69

Target

heart

rate 170 160 150 140 130

(per

minute)

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As a subject becomes more active and able to enjoy more intense activity it may be appropriate during subsequent tests to use a higher “target” heart rate or push to the level of intolerance as indicated by the appearance of signs, symptoms, or electrocardiographic abnormalities such as the following: 1. Subjective symptoms of exertional intolerance a. Severe dyspnea b. Dizziness or near-syncope c. Significant chest discomfort, or pain, suggestive of angina pectoris d. Intense fatigue e. Marked claudication 2. Signs of poor tolerance a. Staggering b. Inappropriate verbal responses c. Facial expression signifying disorders (strained or blank facies) d. Cyanosis or pallor (facial or elsewhere) e. Appearance or accentuation of ventricular gallop sounds or murmurs of valvular regurgitation 3. Blood pressure responses a. The systolic blood pressure usually increases in response to physical exertion. The magnitude of elevation has not been well defined because only a few investigators have measured it routinely in association with graded exercise tests. In a study of 213 healthy adult men between the ages of 20 and 59 years, we foulid that the mean cumulative increase in systolic blood pressure was 66 mm Hg (Table VI) with a mean range from 59 mm in the 20- and 29-year-old subjects to 79 mm Hg in the oldest subject group. The peak systolic blood pressure ranged from a mean of 190 mm Hg in the youngest group to a high of 216 mm Hg in 50-59-year-old subjects. Based on these measurements, we have recommended the exercise testing be terminated if the systolic blood pressure exceeds 250 mm Hg. TABLE VI CUMULATIVE MEAN CHANGE IN SYSTOLIC BLOOD PRESSURE IN HEALTHY ADULT MEN” METS

Age Range (VT) 20-29 30-39 40-49 50-59 Total

Group

4 25 25 26 29 26

5 32 32 38 41 35

6 36 40 43 48 42

7 39 45 47 58 47

9

10

51 61 57 71 60

59 67 61 79 66

8 47 54 51 64 54

a The cumulative increase in systolic blood pressure per MET sured in a group of 213 healthy adult men. There is a progressive from one MET load to the next with a mean cumulative increase Hg at 10 METS.

was meaincrease of 66 mm

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b. A failure to increase the systolic blood pressure in response to increased work loads is considered abnormal. Similarly, a decreasing systolic blood pressure response is abnormal. c. Most investigators agree that the measurement of diastolic blood pressure during graded exercise is inaccurate and, therefore, there are no specific guidelines to offer. In general, the diastolic blood pressure either remains unchanged or decreases slightly in middleaged sedentary men, and an increase of 10 mm Hg or more should be viewed as an abnormal response. 4. Electrocardiographic changes a. Supraventricular or ventricular dysrhythmias or ectopic ventricular activity occurring before the end of a T-wave (“R-on-T” phenomenon). It is recommended that a test be terminated in the presence of three or more successive ectopic ventricular complexes or when their occurrence, without being in consecutive series, becomes significantly more frequent during exercise (about lO/min depending on clinical judgment) b. Second or third degree A-V block c. Major left intraventricular conduction disturbances d. Horizontal or increasingly divergent S-T segment displacement of 0.1 millivolts, or more than 0.1 mV as compared with the resting ECG. These changes suggest that the subject has reached a level beyond which further exertion would be of little added use, might be poorly tolerated or be hazardous. In their excellent “Textbook of Work Physiology” (50) Per-Olof Astrand and Kaare Rodahl make this statement: The question is frequently raised whether a medical examination is advisable before commencing a training program. Certainly anyone who is doubtful about his state of health should consult a physician. In principle, however, there is less risk in activity than continuous inactivity. In a nutshell, our opinion is that it is more advisable to pass a careful medical examination if one intends to be sedentary in order to establish whether one’s state of health is good enough to stand the inactivity! APPENDIX

II

A “Pharmacopoeia” of interchangeable equivalents of various physical activities that can be referred to by the physician would help simplify the formulation of an exercise program. At present there is insufficient data from which to assemble such a document. Energy expenditure exchange. units similar to the caloric intake exchange units found useful in the prescription of diabetic diets are needed and would assist physical educators and therapists help apply the physical activity prescription. The following tabulation is an attempt to provide some assistance in the choice of activities that will be rewarding to the subjects and suitable for independent scheduling outside of organized and supervised programs. The use of METS (muhiples of the metabolic need for sitting quietly) is used because in most activity body weight is

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TABLE VII APPROXIMATE METABOLIC COST OF ACTIVITIES IN METS (INCLUDES RESTING METABOLIC NEEDS) METS 1.5-2

Occupational Desk work Auto drivinga Typing (electric) Electric calculating

machine

Recreational Standing, Walking Flying, Sewing,

playing cards= (strolling 1 mph) motorcycling” knitting

Auto repair Radio, TV repair Janitorial work Typing, manual Bartending

Level walking 2 mph Level bicycling 5 mph Riding lawn mower Billiards, bowling Skeet; shuffleboard; light woodworking; boat driving; golf (power cart); canoeing horsebackriding (walking); bait casting; piano and many musical instruments.

3-4

Brick laying, plastering Wheelbarrow-100 lb. load Machine assembly Trailer-truck in traffic Welding (moderate load) Cleaning windows

Walking 2.5 mph Cycling 6 mph Horseshoe pitching Volleyball, 6-man noncompetitive Golf (pulling bag cart) Archery; sailing (handling small boat); fly fishing (standing with waders); horseback (“sitting” to trot); badminton (social doubles); pushing light power mower; energetic musician.

4-5

Painting, masonry Paperhanging Light carpentry

Walking 3 mph Cycling 8 mph Table tennis; golf (carrying trot); badminton (singles); raking leaves; hoeing; many

2-3

5-6

Digging Shoveling

6-7

Shoveling

7-8

Digging Carrying Sawing

garden light

lO/min

ditches 80 lb hardwood

earth

(10 lb)

power2 m.p.h.; playing

clubs); dancing (foxtennis (doubles); calisthenics.

Walking 3.5 mph Cycling 10 mph; canoeing 4 mph; horseback (“posting” to trot); stream fishing (walking in current in waders); ice or roller skating 9 mph. Walking 5 mph; cycling 11 mph; badminton (competitive); tennis (singles); splitting wood; snow shoveling; hand lawn mowing; folk (square) dancing; light downhill skiing; ski touring 2.5 mph (loose snow); water skiing. Jogging 5 mph Cycling 12 mph Horseback riding skiing; basketball; canoeing hockey; paddleball.

(gallop); Vigorous downhill mountain climbing; ice 4 mph; touch football;

CORONARY

HEART TABLE

DISEASE VII

PREVENTION (continued)

Occupational

METS

117

FORUM

Recreational

8-9

Shoveling

lO/min

(14 lb)

Running 5.5 mph; cycling 13 mph; ski touring 4 mph (loose snow); squash racquets (social); handball (social); fencing; basketball (vigorous). tennis (competitive).

10 +

Shoveling

lO/min

(16+

Running

(L A major excess metabolic some of these activities and

lb)

increase a physician

6 7 8 9 10

mph = 10 METS mph = 11.5 METS mph = 13.5 METS mph = 15 METS mph = 17 METS Ski touring 5+ mph (loose snow); petitive); squash (competitive).

may occur due to excitement, anxiety must assess his patient’s psychologic

handball

or impatience reactivity.

(com-

in

moved. Weight lifting is a clear exception and the external power requirement (work per unit time) can be easily calculated for lifting-not easily calculated for the return. Internal energy requirements to brace the body and move the limbs are also hard to calculate. Many occupational demands are not body-weight related, but the majority of recreational activities, other than home and yard work, involve major elements of moving the body against gravitational pull over distances in a given period of time. Table VII lists the approximate metabolic costs of various activities. It must be appreciated that the contents of Table VII are to be used only as indicative of approximate requirements. Taking the heart rate during or just after a point in tennis, badminton, squash, etc., will usually permit a better assessment of the effect of exertion and be more useful in the discussion of the subsequent activity program than relying solely on this tabulation. The manner in which individuals engage themselves in many activities will cause wide variance in energy expenditure (from the lackadaisical to the frenetic). The first obvious lack in the above tabular attempt is anything concerning swimming-an excellent conditioning activity. Metabolic demands are so dependent on both efficiency (smoothness, coordination) and small differences in speed that we feel unable to give a valid approximation for untrained swimmers-average citizens. Water friction on different hull forms also makes it difficult to estimate the energy used in boating other than canoeing. The effects of cold environment add cardiovascular work requirements due to vasoconstriction as well as potential hazards of dysrhythmia (37,Sl). In prescribing physical activity it is helpful if an individual has had an assessment made of his heart rate response to exertion by stress testing and a calculation of his or her predicted maximum or a maximum actually achieved. Most recreational games should be undertaken initially at an energy utilization that does not exceed 50% of the calculated or defined maximum for the game’s duration even though at times, i.e., while “serving” at tennis, the expenditure may exceed the 50% level briefly.

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Figure 3 permit a useful conversion of heart rate as percent of maximum into percent of maximum energy utilization-max O2 consumption. As indicated earlier it is important in preliminary tes’ting to exceed the probable levels of both metabolic requirement and the usually closely associated heart rate without signs of symptoms of dysfunction before, giving “clearance” for such activities. The “clearance” of highly competitive persons is one of the most persuasive reasons for continuing an exercise test to “tolerance” or “maximum” rather than making calculations from an assumed maximum heart rate. However, where the need for the highest performance is less persuasive one can calculate maximum predicted oxygen consumption per minute per kilogram by use of the rough formulation: Maximum

Heart

Rate = 220 - age (years);

and, by extrapolation of the heart rate response to two or more exertional loads (with heart rates for each preferably over 122/min) on Fig. 4 to the age-adjusted predicted maximum heart rate one can identify the coordinate of the predicted maximal oxygen capacity (Aerobic Power). It may be that the rate of decline of maximum heart rate will prove to be somewhat less than that suggested above but new data of this type probably will not alter the approach to exercise prescription to a major extent. Sheffield’s data (52) is close to Max Heart Rate = 210 - age/2. ACKNOWLEDGMENTS

‘It is a pleasure to acknowledge the great assistance of Denise Ewing, Kathy Mitrick and Sandy Wood in preparing the manuscript and Dr. William L. Haskell and Dr. James S. Skinner for contributions to the concepts inc!eaed. REFERENCES 1.

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