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.
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.
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 obviated.
(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 cell life.
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.
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.
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 us.
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.
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 for men.
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.