It is sufficiently obvious that it is through
muscular activity that we do many necessary, useful, or otherwise
desirable things; and it is also a matter of common experience
that muscular activity is required in order to build up strong
muscles. A very considerable amount of it is required in order
that the laborer may do his work, and a similar amount is necessary
in order that one may become an athlete. But the effects of muscular
activity on the body as a whole are not so obvious; while a large
number of people think that it is "a good thing" and
a smaller number is convinced that it is absolutely necessary
to the best of health, yet we don't infrequently hear men and
women seriously question the latter proposition and even venture
to doubt the truth of the former.
Now there is nothing in hygiene more clearly established than
that muscular activity is absolutely essential to healthy living.
The effects of a sedentary life may not show themselves at once,
but almost without exception, they will assert themselves ill
in the end. Muscular work, in other words, not only enables us
to influence our surroundings, not only builds up strong muscles,
but in other and equally important, though unseen ways, ministers
to the health of the body as a whole.
It is the purpose of this section to present this, the most
important hygienic side of our subject, by describing some of
the physiological effects which muscular activity produces in
the body, and the hygienic value of each of these effects.
1. The Present Use of the Term
In the present chapter, the term" muscular activity"
is used in a somewhat general sense, and without attempting to
set sharp limitations upon it. Strictly speaking, of course,
muscular activity would include all work done by the muscles
of the body, and this is of various kinds. Even those persons
who do no manual labor unconsciously, perform muscular work;
the heart works on, the breath comes and goes through orderly
muscular contractions; sitting and standing, speech, gestures,
mastication, - all these things involve muscular activity, and
do, as a matter of fact, contribute something to the maintenance
of the healthful conditions of the body. It is not improbable
that they are the physical salvation of thousands of people leading
sedentary lives. At the other extreme are those who perform severe
manual labor, or who engage in vigorous exercises or purposely
cultivate exceptional physical strength.
We are not, however, directly concerned at present with either
of these extremes, nor with those forms of muscular activity,
so common today in workshops where, hour after hour, the workman
performs the same task over and over again. We are rather concerned
with those forms of muscular work which are seen in a lumber
camp or on the farm; which present the characteristic of variety
and involve the use of the musculature of the body as a whole;
in short, those forms of activity by which until very recently,
the human race has supported itself in its daily life. Such things
as brisk walking, running, rowing, wood chopping, swimming, tennis
playing, would thus be placed in the same class, since they involve
a use of the muscles similar to those which we have mentioned.
2. The Physiological Effects
of Muscular Activity and their Hygienic Value.
We may now turn to the hygienic value of the more important
physiological effects of these general muscular activities, leaving
for subsequent consideration exercises designed for special purposes,
such as much of our gymnasium work.
(a) The physical and chemical changes in the working organ
are greater than those accompanying any other bodily activity.
The output of carbon dioxide by the body per minute is increased
at once from three- to tenfold with what would be termed moderate
or vigorous exertion, while digestion seldom increases it more
than one fifth, and mental work shows practically no effect upon
it. Large quantities of heat are likewise liberated and the temperature
of the muscle rises several degrees. These physical and chemical
changes are mentioned first because the hygienic effects upon
the body as a whole are to be traced to them as the primary cause.
(b) As the result of these changes in the muscles, new physical
and chemical conditions are introduced into the blood and lymph.
The excess of carbon dioxide is entirely excreted by the lungs,
so that the blood carried to the other organs by the arteries
shows no increase in this substance; but other waste products
(such as salts of sarco-lactic acid), whose elimination requires
the cooperation of other organs than the lungs, are found in
the arterial blood in larger quantities than during rest. The
chemical and physical characteristics of the immediate environment
of every cell of the body is thus changed, and profoundly changed.
Let us now consider the reaction of other organs to these changes
in the muscles and in the blood and lymph.
(c) Some of the most striking effects of muscular work are
those which are connected with the heat-regulating mechanism.
The large liberation of heat by the working muscle necessitates
active measures to get rid of that heat and maintain the constant
temperature. The small arteries of the skin dilate, while those
of internal organs constrict, perspiration is secreted, and all
these processes are carried out in a coordinated manner. The
nervous mechanism of heat regulation is given a new form of activity,
and thus receives valuable training in adjusting itself to the
changing conditions with which it has to cope with daily life.
(d) Closely connected with the foregoing is the (temporary)
relief afforded to any congestion of blood in the internal organs.
Sedentary occupations usually involve more or less overfilling
of the blood vessels of the stomach and intestine, the pancreas,
the liver, the spleen, and the kidneys; they also involve the
absence of those movements of the trunk whose pumping action
affords a marked assistance to the flow of blood through the
abdominal organs. The congestion, thus, is not a good thing;
it almost certainly renders the organs concerned more liable
to inflammatory processes, and, if there has been established
any tendency to catarrhal conditions, it aggravates that tendency.
Popular experience has long associated with health, a good color
of the skin; and, while it is not safe to make such an inference
in all cases, pallor very frequently means internal congestion,
unhealthy digestive functions, and greater liability to cold
in the head or the chest.
(e) Muscular activity is the only thing which can be depended
upon to increase the work of the heart. While this fact makes
caution and moderation necessary for persons having certain forms
of heart disease, yet for the vast majority of people, it is
of the greatest hygienic importance to accustom the heart to
reasonably work hard. Only in this way does it receive the training
necessary for its proper development and for the maintenance
of its strength. Emergencies will arise when the heart is called
upon for severe effort, brief or prolonged. The familiar example
of the sudden "sprint" for a car is a case in point;
and there are times, as in pneumonia, when the issue in sickness
is largely determined by the endurance of the heart. In too many
such cases, if the patient escapes the fatal issue, it is only
with a permanently weakened heart.
It is important not only that the heart should be kept ready
for emergencies, but also that it be kept in condition for vigorous
work as a regular duty of daily life. One of the worst of "vicious
circles," as physicians call them, is the acquirement of
a weakened heart by abstention from proper muscular exertion,
and, as a consequence of this weakened heart, increasing disinclination
to exertion of any kind whatever. The failure to take proper
exercise leads to deterioration in strength and endurance on
the part of the heart; and this cardiac deterioration, with the
resulting discomfort of breathlessness, leads in turn to abstention
from muscular activity.
(f) Muscular exercise is the one agent which increases the
depth and frequency of the respiratory movements. The hygienic
importance of this does not lie in the better oxidation of wastes,
since, so far as we have any accurate knowledge on the subject,
it would seem that the processes of respiration during sedentary
life more than supply the existing demands of the tissues for
oxygen. The increased respiration is rather of importance because
of the secondary effects of the respiratory movements in promoting
the flow of blood, and especially the flow of lymph.
It is probable that the" freshening effects" of
muscular exercise are to its very large extent, attributable
to the improved lymph circulation in the tissues, and this effect,
it will be remembered, is felt in the immediate environment of
almost every cell in the body. The suction action of inspiration
quickens the lymph flow from all organs outside the thorax, and
the increased pumping action of the respiratory movements themselves
aids the lymph flow from the lungs and other organs within the
thorax. Waste products are more completely removed from the lymph
spaces surrounding all cells, and thus one of the most important
fatigue conditions is relieved. Where lymphatics are subject
to the pumping action of contracting muscles and of the alternate
flexion and extension of joints, the suction action of the respiratory
movements is re-enforced. This pumping action, especially affects
the lymphatics of the arms and legs, and those of the abdominal
cavity (through the action of the diaphragm and the trunk movements).
The increased respiratory movements also contribute to greater
mobility of the ribs and to the better ventilation of the lungs.
During vigorous exercise, all lobes of the lungs are used, and
the dangers attendant upon disuse of the apical lobes are largely
(g) Moderate exercise exerts a favorable effect upon the digestive
organs, although the precise action involved is very complicated.
Here also, it improves the lymph flow, thus promoting absorption
and producing better conditions in all digestive glands and in
the muscular apparatus of the digestive tract; it prevents continued
congestion and the unfavorable attendant conditions. It is probably
also a direct stimulus to peristalsis, for unquestionably, the
exercises which involve movements of the trunk often prove a
peculiarly efficient remedy for constipation.
The above summary is very far from a complete enumeration
of the effects of muscular exercise upon the organism, but it
will suffice to show how essential an element such exercise is
in the life of the body. The training of the heat-regulating
mechanism, the training of the heart, the improved lymphatic
environment of every cell resulting from increased breathing
movements and from the pumping action of mechanical motion, the
relief of internal congestions and the favorable influence upon
digestive functions, - all these things are fundamental to healthful
3. Muscular Activity a Necessity
We often hear of men and women who live to old age and do
large amounts of mental work with seemingly little or no muscular
activity; and it is sometimes suggested that the experience of
these people proves that exercise is unnecessary. There are also
on record a few cases of men who can drink large quantities of
whisky without getting drunk; but it will not be contended that
most men can do likewise. As to any line of right hygienic conduct,
there are some among the hundreds of millions inhabiting the
earth who can do the reverse with impunity; but they are not
to be taken as safe guides. The cases are very few indeed where
abstinence from muscular activity persisted in as the rule of
life is without disastrous results; the bad effects do not always
come in a day or a week or a year, but sooner or later they almost
invariably show themselves. We must never fail to distinguish
carefully between the immediate and remote effects of any line
of conduct; and nowhere is this caution more needed than in observing
the effects of a sedentary life, the evil results of which, though
sometimes long postponed, usually appear sooner or later.
Some muscular exercise is a hygienic necessity for every period
of life; it belongs to no one age. Youth is the time when athletic
sports, games, and all kinds of activity are most agreeable,
most necessary, and most enthusiastically pursued. In old age,
the changes which take place in the arterial walls necessitate
caution as to severe exertion. But these are only the extremes.
Rarely indeed do we meet with people who would not be benefited
by a walk of several miles a day, at a rate of three or four
miles an hour; and it cannot be too strongly insisted that the
inability to do this with enjoyment and profit is in almost every
case because the habit of taking exercise is not kept up. The
heart is not as strong as it once was; the connective-tissue
elements of the muscles, the ligaments, etc., become sore upon
taking exercise, not because of any inevitable "old-age
change," but because the ability to do the work easily has
not been maintained by constant practice.
It would be amusing, if it were not sad, to see how the average
adult American will try almost everything which holds out the
slightest promise of maintaining some sort of health rather than
take muscular exercise, -alcoholic drinks (to dilate cutaneous
vessels), Turkish baths, massage, patent medicines, - anything
rather than a horseback or bicycle ride, or a brisk walk, or
some other simple and perfect remedy which stands within easy
reach. It is not to be expected that when these exercises are
first tried after years of sedentary life, they will be enjoyed;
and too often the man or woman, instead of persisting patiently,
draws the conclusion that the time for such things has gone and
only resignation to old age is in order. When young men and women
begin life, it should be with a clear conception of the danger
of falling into habits of muscular inactivity, and with a conscious
and strong determination to avoid this danger.
4. The Conservation of the
Enjoyment of Muscular Activity.
Muscular activity is so necessary for health, for the enjoyment
of life, and for usefulness, that the ability to take it should
be conserved at all costs. We should not only keep "in practice"
by making it as much a daily habit as eating or sleeping, but
we should also avoid those unfavorable conditions which interfere
with our enjoyment of it. Some will not walk a step more than
necessary because, by the use of improper shoes, they have acquired
deformed feet, unable to support the weight of the body; sometimes
a sunstroke, following incautious exposure to the hot sun, leaves
the heat-regulating mechanism so injured that muscular exertion
except in cool weather becomes unsafe or even dangerous; exposure
to dampness often brings rheumatism, an almost insuperable barrier
to pleasurable movement of any kind; some infectious diseases
leave their trace in the form of an incurable organic weakness
which makes muscular activity inadvisable. These things should,
of course, be avoided for their own sake; they should be avoided
also because of their serious indirect effects on health.
5. General Character of the
Most Useful Exercises.
To specify the exact forms or amounts of muscular exercise
advisable would take us beyond the scope of the present work.
Here as elsewhere, the student must work out his own salvation.
In the following chapters we shall discuss, as far as possible,
the characteristics or some special exercises; for the present
a few general suggestions may prove useful. The muscular activity
which formed part of the life of our ancestors may be described
as generally moderate, though at times vigorous or hard; only
exceptionally did it involve extreme endurance or great muscular
strain. Our ancestors were not, as a rule, given to "tugs
of war" or to putting up heavy dumbbells, or to making inordinately
long runs, or to "giant swings" in the gymnasium; nothing
like a hundred-yard dash or a four-mile boat race was a common
occurrence among them. Where work of this kind had to be done
it was left - to those who, by reason of exceptional strength,
were especially fitted for it; mankind as a whole did no such
work, and it is not necessary (or even advisable) for most of
Nor can it be claimed that the cultivation of great muscular
strength was a common practice. There was a much higher average
of strength than among us, and we should probably be better off
where our average higher than it is;
But if we can judge at all from the history of mankind, such
training as that required to break some college strength test
is not demanded for hygienic purposes. Nor does our own experience
tell a different story. Very strong men are no healthier nor
longer-lived than those of only average strength, and, in general,
the athletic ideal is not the hygienic ideal. It is not necessarily
unhygienic, but it is not required for purposes of health.
It is not desirable that exercise taken for general hygienic
purposes shall be unduly fatiguing. A moderate amount of fatigue
is not unwholesome, since fatigue brings with it the desire for
rest; nor is fatiguing exercise necessarily harmful. But, exercise
need not necessarily be of this character; and, in view of the
other work of life, it is certainly better to avoid undue fatigue,
especially when we cannot rest well afterwards. A walk of six
or eight miles will do more good than one of forty or fifty.
6. Exercise for Women.
Muscular exercise is no less essential to the health of women
than of men. Fortunately, the day is past when false standards
misinterpreted the truth that woman's most natural sphere in
life is the home to mean that, tied down to the confining duties
of household life, she should never know the joy of movement,
except in dancing (and sometimes not even in that); and then
proceeded to make sure of the result by clothing her in narrow,
pointed, high-heeled shoes, heavy skirts, and tight-lacing corsets.
The reaction from this state of affairs, at times going to the
opposite and undesirable extreme, has unhappily at times produced
in women exhibitions of mannishness which once led a lady to
speak of "that terrible thing called muscular exercise."
But disgust with these grotesque but avoidable consequences should
not be allowed to blind us to the fact that a reasonable enjoyment
of daily muscular activity is as much a necessity for women as
Hough T & Sedgwick WT (1906). Muscular Activity (Chapter
XVII), The Human Mechanism Its Physiology and Hygiene and The
Sanitation Of Its Surroundings, Ginn & Company, pg 305-313.