ACQUIRED DISEASES FROM MUSCULAR OVERWORK AND STRAIN.
Muscular exercise carried out systematically and reasonably is an essential part of a healthy life. The muscles left inactive are exceedingly apt to undergo degenerative change, and to produce, in comparatively early life, a feebleness of body which is fatal to the full enjoyment of the term of life that is naturally allotted to us. But, useful as it is, muscular exercise may be carried to the extent of producing disease and of materially shortening the period of existence.
When muscular exertion is carried beyond what is reasonable, two unnatural conditions, one local, the other general, follow. The local unnatural change instituted belongs to the muscle or muscles subjected to the excessive work. We see this in the enlargement of particular muscles, as in the enlargement of the muscles in the arm of the blacksmith and in the leg of the dancer. We say that the muscles in this state are hypertrophied, and al though they may be more competent, for a time, to perform the particular act for which they are employed, they are, in fact, out of harmony with the rest of the body, and are, therefore, in the strict sense of the word, diseased. Later on the local condition in the muscle or muscles thus overworked may change from a state of undue strength to one of deficiency of power. The muscular fibre may undergo degeneration, and he charged with new ele ments which have not the contractile property; or, it may un dergo wasting of structure and loss of working capacity from that cause.
The general mischief which arises from over-muscular exer tion is the most serious when it affects or influences the involun tary muscular organs on which life depends; the muscles and parts engaged in the circulation of the blood; the muscles of respiration; and the organs of digestion. When once one of these fails, the failure of the body altogether is inevitable.
Sometimes the effect of muscular overwork tells primarily upon the body through the stomach. A person who is altogether in fair health becomes conscious of the fact after he has per formed a certain amount of muscular labor which he may con sider as not greatly in excess of his capacity, that he has a painful sinking and failure in the stomach which nothing but complete rest can rectify. Afterwards he is dyspeptic, and for some days loses his natural aptitude for taking and digesting food.
In another person the failure commences in the respiration. There is experienced after fatigue from muscular exertion some want of breathing power, a sense of weariness in breathing, a weight and oppression, or a tightness of the chest with a little cough and not uncommonly an ache, extending from the breast bone through the chest, with a slight spasm. Nothing relieves this condition but rest, rest which may, perhaps, be required for several days.
In a third class of persons, and by far the largest class, the first signs of general failure are indicated through the circulation. The heart, it will be remembered, is itself a muscle. It is the central mover of the bodily life, and the physical life altogether rests upon it, if I may so express myself, as upon an inverted cone. Its work ever going on involuntarily night and day, cannot be disordered without communicating some derangement to the whole organism. The effect of this is, that the heart soon begins to undergo modification of structure under prolonged over-exer tion. At first its nutrition is increased; then it becomes over active and over-powerful, and in time holds a relationship to the body at large which is out of proportion, in respect of balance of power, with the rest of the body.
Presuming that the excessive exercise to which the heart is subjected is carried out early in life, while there is yet elasticity of the other vital organs, the body may adapt itself to the in creased pressure and motion, and so, in the early period of pleted life, the balance may be restored and a healthy balance secured. If it be asked, why should not this healthy balance remain ? the answer is plain. It will not remain because the elas ticity is not persistent. As the body becomes developed and its structures firm, the resistance to the stroke of the heart increases, and the heart begins to bear a load which oppresses it beyond the work that is put upon it. Moreover, as its own nutrition becomes less active, its own elasticity is impaired. Thus it, in turn, gives way before the resistance. It becomes relatively feeble, and with its feebleness all the rest of the organism necessarily sympathizes.
In one of my studies I calculated up what may be considered the complete numerical value of the strokes of the heart of a per son who has lived to fourscore years. The numerical value of beats or strokes may be fairly taken at about three billions, which will have been delivered at the rate of rather more than one hun dred thousand per day. The heart which accomplished the three billions of beats in the eighty years is estimated, in this calcula tion, as performing a fairly natural life, and we will suppose that, according to the construction of the organism to which it be longed, it carried out its fully-allotted task. It worked eighty years and made the three billions of strokes, which was its limit of work done, in the time named. If it had been the heart of a postman, its work would have been increased a good fourth during the period of increased activity, and we may deduct from the time when its increased activity commenced a fourth of the value of the life. If then overwork commenced at twenty years of age, a fourth part of the remaining years due might fairly be deducted, bringing the duration of the life that should have been eighty years to sixty-five years.
I do not give this as more than an approximate calculation, but it is not far from the truth, and the day will come when calculations will be made sufficiently absolute to supply correct valuations for estimating the value of life in persons following all laborious muscular occupations.
In the cases where excessive muscular fatigue induces constitu tional failure, leading to premature death through the circulation, the heart becomes enlarged in the first stage; the blood-vessels become unduly taxed in the second stage; the elasticity of the blood-vessels declines and resistance increases in the third stage; the heart becomes enfeebled in the fourth stage, degenerated in the fifth, and incompetent for its functions in the sixth. In a seventh and final stage, one of premature old age and decay, some of the other vital organs, lungs, liver, kidney, or brain, follow their leader in failure of function, and death closes the scene.
In certain instances it happens that the heart itself is the mna cular organ first affected by the exercise. Under the exertion the organ may suddenly fail altogether, losing its nervous power, and becoming intermittent or irregular in its action. I have known this accident to occur in the most varied ages of life; in youth, in full age, in mature, and in advanced age. Or the heart may un dergo, from the first, an enlargement, may work with a force that is out of proportion to everything that is required of it, and may become a centre of disturbance to all the other systems of the body. This is by no means an uncommon result of excessive muscular effort and strain, and, indeed, I may state that amongst the many persons who have come before me suffering from over physical endurance in its early stages there have been very few in whom the heart was not too large and too powerful. In later stages the enlarged and over-taxed heart is apt to undergo degen eration, to lose its contractile elements, and to become a centre of derangement to the body generally from failure rather than from excess of duty.