Editorial
Physical Fitness and Cardiovascular Health
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active tissue, but interindividual variations
may be large, and the value of these predictors in populations of varying ages, sex,
and body size requires further study. V),,
max can be predicted from various submaximal step, treadmill, and bicycle tests, with a
conservative accuracy of ± 12%, but submaximal tests should only be used for population
surveys when the relationship between the
predicted and the actual maximal oxygen
uptake values are known for the population
under study.4
Problems arise in applying Vo, max results
to population groups in different parts of the
world because of differences in methodology
and because of errors inherent in measuring
oxygen uptake outside the research laboratory.
It is not certain how to allow for differences
in body size and build, for obviously a 90-kg
man should have a higher oxygen transport
capacity than a 60-kg man. To measure an
individual's fitness for moving his mass from
point A to point B, division of the observed
oxygen uptake by body weight may be valid,
and yet the use of weight as a reference point
may not accurately reflect the pumping
ability of the heart. It has been suggested
that lean body mass (LBM) should be used
as the reference point for VO max to judge
cardiorespiratory fitness. In large population
studies, it is not practical to measure LBM
with densitometry or chemical methods, although LBM can be predicted from skinfold
thiskness, and whole body counters to measure total body potassium are available in
some areas. Some difficulty is encountered,
however, in translating total body potassium
measurement into an absolute quantity of
LBM, and the correlation of LBM with fitness
measurements is yet to be done on a large
heterogeneous group. Buskirk and Taylor5
found that Vo2 max was most closely correlated with active tissue which is lean body
V ARIOUS ASPECTS of muscular exercise
and physical fitness have been discussed
at several recent symposia, bringing together
physical therapists, physical educators, nutritionists, exercise physiologists, epidemiologists, practicing physicians, and other
disciplines of the health profession. Most
workers close to the field of physical fitness
feel that it is a good thing to have; yet most
will admit (at least secretly) that absolute proof
of this fundamental point is still lacking. This
report is intended to survey some of the current knowledge and problems in fitness research, much of which was revieved at a
recent symposium in Toronto.'
Physical fitness still defies exact definition
or measurement, partly because fitness is a
multifaceted qualitative parameter that is
usually specific to the task involved, and the
scores of the many different tests available to
measure fitness are not closely correlated.2 To
escape this dilemma, there is a tendency to
oversimplify the situation by considering a
supposedly definable parameter (aerobic
power, maximal oxygen uptake [Vo2 max])
as the best single measure of overall fitness.
During exercise, cardiac output levels off before V02 max is reached3; pulmonary ventilation, diffusion, and the capacity of the
respiratory muscles have approached maximal
values; and the exercising muscles are almost
fully taxed. Although in normal subjects the
exact factor limiting maximal oxygen uptake
is unknown, a disorder of the cardiac, respiratory, or musculoskeletal systems usually
results in the involved system becoming the
limiting function. Vo, max is closely correlated with heart volume, vital capacity, total
body hemoglobin, lean body weight, and
From the Department of Cardiology, The Children's
Hospital of Winnipeg, Winnipeg, Manitoba.
4
Ciri ulation, Volume
XXX7II, Ja,-uarO 1968
EDITORIAL
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mass minus bone mass. This important study
showed that per kilogram of active tissue the
VO2 max of athletes was higher than that of
sedentary subjects, indicating that the oxygen
transport and muscular systems in trained
subjects are qualitatively, as well as quantitatively, superior to those of untrained
subjects. The higher oxygen uptake of the
athlete is not simply due to an increase in
muscle mass, but seems to be related to
a greater capacity of the heart and lungs to
deliver oxygen, and of the muscles to utilize
oxygen. There may be an inborn limit to the
aerobic power that any individual can attain
with training, and Holmgren6 has suggested
that a true index of fitness would be the
percentage of the potential that the actual
power is. Application of this interesting concept would require each subject to undergo
intensive physical training for an undetermined duration of time and would be impossible to apply to population studies.
Other difficulties arise from our lack of a
firm definition of fitness. Aerobic power may
be normal in the presence of minor anomalies,
such as hypertension, mild anemia, diabetes,
or gastric ulcer. Any population study of fitness must, therefore, include a comprehensive
medical examination. Exercise ECG changes
pose a particular problem. Who is more fitthe subject who can complete a work load of
1,200 kpm on the bicycle reaching an 02 Uptake of 3 L/min having an S-T segment
depression on his electrocardiogram of 3 mm;
or a subject who plays out at 700 kpm, at 2
L/min of 02 uptake, while his ECG remains
stable? In other words, is the heart showing
evidence of strain at a cardiac output of
about 21 L/min better off than the heart that
is working maximally at 18 L/min while showing no evidence of coronary insufficiency?
ECG changes after milder exercise, such as
the double Master's test, generally indicate a
high probability that symptomatic heart disease will develop within the next 5 to 10
years.7
Population surveys of aerobic power are
available in several areas of the world but
comparisons are difficult because of differences
Circulation, Volume XXXVII, January 1968
5
in methodology and, in particular, because
the test subjects have not been randomly
selected. Some of these problems should be
corrected shortly by studies underway for
the International Biological Program. In children over 8 years of age, maximal oxygen
uptake varies considerably. High values re-
ported from Sweden are likely due to the
selection of children engaged in more active
physical education programs. In average male
adults from 40 to 60 years of age, fairly similar
maximal oxygen uptake values have been
reported from several different centers.8 Active
participation in sports past age 40 delays the
25% decline in aerobic capacity that occurs
between ages 20 and 60.9
Considerable interest has been shown in
the fitness of some of the primitive societies
who require muscular work in order to survive. The aerobic power of these people
should theoretically be higher than that of
modern societies. Comparative studies have
methodological and logistic problems and are
further complicated by other factors such as
poor nutrition that might affect the results.
Lange Andersen'0 has found that the aerobic
power of the Lapps from the Northern Scandinavian peninsula was clearly higher than
that of Oslo workers at all ages, and particularly after age 40. Studies on small numbers of subjects suggest that the aerobic
power of other primitive men, ranging from
the Arctic Eskimo to the Kalaharian bushman,
may be slightly above that in urbanized populations when presented as milliliters per
kilogram of body weight.10 However, as these
native people are usually extremely lean with
a low body fat content compared to their
urban counterparts, expressing the uptakes in
milliliters per kilogram of lean body mass
would likely show the urban man to have the
higher aerobic power.
The main concern of cardiologists is whether there is any relationship between physical
fitness and the frequency and morbidity of
coronary heart disease. With the exception of
a preliminary study on a native population,"
there is no available information on the relationship of maximal oxygen uptake or other
6
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measures of fitness to coronary disease rate.
This problem has been approached indirectly
by assuming that men with physically demanding occupations are more active and
possibly more fit than those with sedentary
occupations. Most of these population studies
on various occupational groups (recently reviewed by Fox and Haskell'2) have suggested
that inactivity at work may increase the morbidity and mortality from coronary heart
disease, but it is not known whether the
occupational categories selected for study
have detectable differences in their fitness
levels. The lower incidence of coronary heart
disease in the more active worker may have
been due to factors other than different levels
of fitness, that is, differences in personality,
levels of occupational emotional stress, body
build and composition, and recreational habits. The weekly energy requirement of individuals in each occupational category should
be assessed. The questionnaire method tends
to exaggerate grossly the time spent in physically active pursuits.'3 A careful and detailed
activity diary is the most suitable method
currently available. A tape-recorder pulse-rate
diary is simple to obtain but has the drawback
that emotional factors may account for more
tachycardia than physical exertion. The direct
measurement of metabolic demands of daily
living by oxygen uptake measurements is
cumbersome to apply on a large scale.
May we assume that the subject more active
in his work and play has a higher fitness level
using aerobic power as the measure of fitness?
Some of the available evidence suggests that
either the V02 max test is not sufficiently discriminatory or that the light demands of most
occupations have little effect on aerobic power.
Norwegian lumbermen, 20 to 30 years of age,
have the same aerobic power as Oslo white
collar workers, while lumbermen from 30 to 60
years of age are only 3 to 5 ml/kg superior
to the office workers.'4 In Winnipeg, the
V02 max of insurance salesmen was 5
ml/kg/min below that of relatively heavy industrial workers 30 to 60 years of age.8 In
Montreal, there was no difference between the
work load at a pulse rate of 150 beats/min be-
EDITORIAL
policemen or firemen and white collar
workers when body size was taken into consideration.'5 If the aerobic power of white
collar workers is only a little below that of
lumbermen, can we expect significant differences between the postal clerk and postman,
or the bus driver and the conductor? The
duration that a maximal load can be sustained
declines after thermal or exercise stress while
V02 max is unchanged,'6 and it is likely that endurance tests at relatively high work loads are
more discriminatory than V02 max in separating the fit from the unfit, but endurance testing may not be suitable for population surveys.
It remains to be proven that the VO2 max
measurement is any better than some of the
less sophisticated tests measuring a simple
parameter such as recovery heart rate in discriminating between fit and unfit subjects, or
those who are likely to develop and those who
have some natural protection from coronary
heart disease.
Investigators interested in the role of exercise in the prevention or treatment of coronary
heart disease need hardly apologize for their
inability to provide conclusive answers, for
exercise cannot be put into a capsule, the
dose is difficult to gauge, a real effort is required on the part of the patient, and the effects of the therapy are not easily measured.
Contrast this with a pill that is easily administered, with little effort required on the part of
the patient; with a dose that may be accurately titrated against its effect on the patient's blood; yet the value of long-term anticoagulant therapy in coronary heart disease
also remains controversial.17 Future population
surveys into the incidence of coronary heart
disease hopefully will measure fitness with
one of the available submaximal tests, but
unfortunately answers to the questions-Does
physical fitness delay the development of
coronary heart disease or prolong life? What
is the optimal level of fitness? What facets of
fitness are most desirable for health and longevity? How is this fitness best achieved?
-are likely years away.
It is becoming popular to have patients
who have recovered from acute myocardial
tween
Circulation, Volume XXXVII, January 1968
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EDITORIAL
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infarction take part in physical exercise programs, and these programs have definite
merit in improving patients' morale and facilitating full rehabilitation. As patients recovering from myocardial infarctions, statistically
speaking, follow a predictable course, it should
be possible to decide clearly over a period
of 5 years whether these programs do anything for patients other than improve their
well-being. However, to decide this important
matter, a series of consecutive patients recovering from myocardial infarction should
be referred to a rehabilitation center with one
subject undergoing physical training while a
matched control takes part in an equal number of sessions of nonathletic recreational
programs. Realizing the dangers of generalization, it is suggested that the better the
control of past studies in coronary heart disease, the less the benefit that can be shown
to result from measures such as anticoagulants or antianginal agents. None of the exercise rehabilitation studies in coronary disease
so far available for review have made any
attempt to achieve the necessary levels of
control.
Discussion of the value, or lack of value, of
physical fitness will go on for many years.
Even if it can be shown that a high level of
physical fitness reduces significantly the incidence and mortality of coronary heart disease, a major problem confronting public
health officials is to motivate people to want
fitness badly enough to do something about
it. Much work remains to be done, but the
Toronto symposium showed that physicians
and physical educators, and others in the
health professions speak the same language
and hopefully will work more closely together
in the future.
G. R. CUMMING
References
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Physical Fitness and Cardiovascular Health
G. R. CUMMING
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Circulation. 1968;37:4-7
doi: 10.1161/01.CIR.37.1.4
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