Thus it is that muscular movement is useful in all disorders of nutrition, and that bodily exercise is a necessity for all constitutions.

But we must not conclude that the benefit of exercise is equal in all cases, whatever may be the quality of the work done. If muscular movement produces a series of identical general effects in all constitutions, the different exercises we have considered in the fourth part of this book have all of them their special effects.

We cannot enter here into details of application, and reserve for another volume the complete study of the Therapeutics of Exercise. It will be enough to recall, in finishing this chapter, how the special effects of exercise may vary according to its kind and its dosage.

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We have seen that work has two opposite influences on nutrition it increases the gains, and it also increases the losses of the system. The hygiene of work essentially consists in balancing these two opposed results; but certain conditions of exercise may make now one, now the other, predominate, and it is possible to obtain almost at will, by the aid of muscular work, either an increase or a diminution in the weight of the body.

An example borrowed from Dr. Worthington's book on "Obesity" will suffice to show how work can lead, according to the details of its application, to diametrically opposed results. On the Marne, between Alfort and Chateau-Thierry, two teams of horses worked on a towing path, drawing boats. The first team drew up stream, walking; the second down stream, but trotting. This course was, for each team, the only work of the day. As far as the quantity of work done each day was concerned, the horses which walked executed a greater number of kilogrammetres, since they went the same distance, but against the current; the horses coming down stream drew a lighter load and covered the same distance; but, in spite of the difference in the quantity of the work, the swiftness of their pace completely changed for them the results of the work; the horses which did their work at a trot got thinner, those which walked, gained weight.

CHAPTER II.

EXERCISES WHICH DEVELOP THE CHEST.

Importance of Oxygen in Nutrition-Advantages of a great Development of the Chest-How this Result can be obtained by Exercise-Received Opinions on this Subject-Our Reasons against them-By what Mechanism the Chest is DevelopedForced Breathing-Pressure from within outwards—Increased Breadth of the Shoulders not to be Confused with Increased Size of the Chest-Conditions which Develop the Chest-Amplitude of the Respiratory Movements-Opening out of the Pulmonary Air-cells-Increase of the Respiratory Need-The Chest of Mountaineers-Exercises which produce a Thirst for Air" Exercises suitable for Developing the Chest-An unexpected conclusion: Superiority of Exercises of the Legs to those of the Arms-Running and Skipping.

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THE quantity of air introduced into the system at each respiration is regulated by the capacity of the lungs Now we have seen in the preceding chapter that the acquisition of a great quantity of oxygen is one of the most useful results of bodily exercises.

It is then of great importance to define the conditions in which muscular work is capable of increasing the size of the cavity in which the lungs are contained.

At first sight we should be inclined to believe that the exercises performed with the upper limbs, which are moved by the muscles of the shoulders and trunk, to be those most likely to raise the ribs; and in fact exercises of the arms are generally regarded as excellent for increasing the respiratory power.

It will be enough to quote and criticise a very conscientious study by Demény,* to show the fallacy of this opinion.

Georges Demény. De l'Education Physique.

"We have determined," says this author, "that there are various degrees of exercise favourable to the dilation of the thorax.

"The attitudes in which the scapulæ, drawn back and fixed by the tonicity and by the contraction of the rhomboidei, trapezia, and latissimi dorsi muscles, serve as fixed points for the elevators of the ribs, these attitudes, of which the type is the soldier at attention, the body upright, the belly retracted by the aspiration of the thoracic viscera, produce a manifest dilation of the thorax.

"Still more a slight backward motion of the arms, rotation outwards, abduction, and most of all the vertical elevation of the arms, as in passive suspension with the arms at full length, raise the ribs to a maximum degree, and give to the costal cartilages a mobility which allows of great inspiratory movements, and opposes the fixation of the thorax in the position of expiration."

These conclusions are preceded by very interesting considerations on the muscles which are brought into action in these attitudes, and the author clearly demonstrates that inspiratory muscles are brought into action. Their two extremities are separated in these attitudes, and the muscular tone tends to draw the movable points of attachment, represented by the ribs, nearer to the fixed points of attachment represented by the scapula, the clavicle and the humerus.

Demény's conclusion is that more air enters the chest in the attitudes he describes, than in the condition of repose. It is certain that in these attitudes the ribs are very strongly raised, but the author condemns himself by remarking that the thoracic aspiration draws up the abdominal viscera under cover of the ribs, so that the diaphragm is thrust upwards.

If we try to define the respiratory advantages gained by this manœuvre, we see that it puts into forced action all the inspiratory muscles except the diaphragm, which remains in the position of expiration, for it is pushed up by the abdominal viscera. Now if a man, keeping his hands in his pockets, takes the trouble to take a very deep inspiration, he will be able to raise his ribs to the

greatest possible limits, and further, he will find that his diaphragm will share in the movement, and will push down the abdominal viscera, instead of allowing itself to be thrust up by them into the chest. The vertical diameter of the thorax will thus be increased, while before it was diminished by visceral aspiration, and in the end, it will be found that the most ingenious gymnastic combinations are not as efficient in increasing the intra-thoracic space as are profound expirations made during repose.

The conclusion from this is, that the best athletic exercise for increasing the size of the chest is that which compels the deepest inspirations.

Before developing this idea we must explain the mechanism in virtue of which a temporary amplification of the thorax can in a short time produce a lasting increase in its capacity. But we must first remark that it is of no advantage in respiration to increase the thickness of the thoracic parietes, if the cavity remains small; it is the intra-thoracic space which must be amplified in order to increase the respiratory power.

Now there is only one way of increasing this space, and that is to increase the volume of its contents, the lungs.

It would be illusory to set any value on the elevation of the ribs, on a favourable direction of the costal articulations, on the strength of the inspiratory muscles, etc., if the lungs were not increased in size at the same time as the thoracic cavity is dilated. If the lungs become weakened, the upper ribs fall in, and the best formed chest becomes flat. An empty thoracic cavity is incompatible with raised ribs, and do what we will an empty chest assumes the position of inspiration.

We see this every day after the absorption of pleuritic effusions, when the lung tied down by false membranes is incapable of returning to its normal size, and perhaps is reduced in volume by one half or two thirds. However powerful the inspiratory muscles, whatever the direction of the costal articulations, the ribs cannot be raised, for a vacuum cannot exist in the pleural cavity.

Thus, in the thorax, the volume of the receptacle is determined by the size of the contents. If you wish to develop the chest, do not try to raise the ribs, but try to inflate all the air-cells of the lungs ; you cannot do it by any mechanical means, and the most clever combinations of muscular movements give but an incomplete result when unaccompanied by the movement-voluntary or instinctive of forced inspiration.

The experiments of M. Demény certainly prove that the gymnastic attitudes he describes are the most efficient in raising the ribs; but they also prove that the raising of the ribs, carried to an extreme, does not suffice to give a maximum size to the lungs, for when the ribs are raised, the diaphragm goes deeper into the thorax and the abdominal viscera rise. The respiratory field thus loses at the base of the chest what it gains at the apex.

The momentary amplification of the thorax during inspiration may indeed lead to energetic contraction of the inspiratory muscles; but a definite increase in size, persisting during repose, can only be brought about through increased volume of the lungs.

How is it that the lungs can increase in size through athletic exercise? By a mechanism well known in physiology, by the filling out of certain air-cells ordinarily inactive, which only come into play during forced inspiration. The expansion of the pulmonary vesicles is complete in proportion to the quantity of air introduced. The atmospheric air drawn into the lungs by a very powerful inspiration seeks out the most obscure corners, and inflates the air-cells of certain regions which ordinarily have no part in the respiratory function.

A definite increase in the volume of the lungs is the consequence of frequent repetition of this supplemental respiration. The air-cells which are as a rule inactive, and which are reserved for cases of excessive respiratory strain, arise from their inaction; their walls, which are usually collapsed, and even stuck together, separate and