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CHAPTER I.

PHYSIOLOGICAL CLASSIFICATION OF BODILY EXERCISES.

Quantity of Work done in an Exercise-Gentle, Moderate, and Violent Exercises-Quality of Work in Exercise-Exercises of Strength, of Speed, and of Endurance.-Mechanism of the various Exercises.

We have just studied the general effects of muscular work on the organism which performs it. If we endeavour to sum up the conclusions to be derived from this study, we see that the results of work vary according to the quantity done and the method in which it is done.

Exercise performed without moderation or rule induces all forms and all degrees of fatigue, and exposes the human machine to the various injuries which we have described as the accidents of work.

On the other hand, muscular work performed in gradually increasing quantity and according to the rules of graduated training, brings about a progressive adaptation of the organs to the performance of more and more violent exercise. It improves the human motor by giving to all its machinery a greater strength and ease of working.

Such are the results of exercise considered as an abstract factor and reduced to the quantity of work represented by it. But it is only by a mental effort that we can isolate the work done by the system, from the organs concerned in its performance. Now these organs are not the same in all cases, and do not work in the same manner in all forms of exercise. Thus the practice of different exercises produces different effects on the system.

Hence the use of a rational classification of the different exercises, and the necessity of making a choice from among them in accordance with the effects desired.

At the outset we notice a difference between the various exercises practised: they do not all necessitate the same quantity of work. Exercises are called violent when they demand considerable and repeated efforts from the muscular system; they are called moderate when they do not demand much work: finally, when the muscular exertion is reduced to a minimum, the exercise is called gentle. Running is a violent exercise, walking at a fair pace is a moderate exercise, and walking slowly is a gentle exercise.

The quantity of work done is evidently the chief element in the classification of bodily exercises, for it is that which most influences their effects. But, the amount of work done by the system being the same, it is not indifferent, from the hygienic standpoint, whether the work is done slowly or quickly, whether it is uninterrupted, or there are frequent periods of rest. It is important also to know if the exercise needs complicated and difficult movements, if it exacts great attention of the will, or if it can be performed automatically, and without needing the intervention of the conscious faculties.

Finally, besides the different forms of the work, it is also important to determine the mechanism of the exercise, to say what parts of the body are especially concerned in its performance, and what are indirectly associated with it. This is one of the least known points in the therapeutics of exercise, for the analysis of the different exercises of the body has not yet been made in a satisfactory manner. It is however one of the most interesting and most practical points in this branch of hygiene, for upon the intimate mechanism of an exercise depend its local effects. A bodily exercise is often prescribed with an orthopedic object, but we cannot exactly foresee its effects unless we know exactly which group of muscles performs the work, which

articulations and which bony levers support the pressures and the shocks, and by what attitudes the whole of the body associates in the movement of the regions at work.

A physiological classification of bodily exercises, taking especially into account the effects produced on the system by the different exercises, must have for its basis three elements: the quantity of work which they need, the nature or quality of this work, and finally the mechanism by the aid of which the work is performed. But these three elements of classification are combined in so varied a manner in the different exercises practised, that they cannot logically serve for their grouping. Some exercises allied by the quantity of work they represent, differ in the mechanism of their performance; others, on the contrary, are similar as regards movements, but differ in the intensity of the work.

So these three elements, quantity, quality, and mechanism of work, will not be taken here as the basis of a systematic classification of exercises. They will rather serve as landmarks to guide us in the physiological analysis of these exercises, and as labels for their grouping in categories corresponding to certain effects, now salutary, now harmful, according as they conform to, or are in opposition to, the indications furnished by the temperament and morbid state of the patient.

CHAPTER II.

VIOLENT EXERCISES.

Violent Exercise must not be confounded with Fatiguing Exercise -Difficulty of appreciating the Quantity of Work expended in an Exercise-Difficult Movements-Feats of Strength— Gymnastic Pedants-Children's Games and Gymnastics-Skipping compared with Climbing a Rope-Analysis of Exercises -How the Physiological Effects of Work may indicate its Degree of Intensity.

THE quantity of work represented by an exercise is the basis of the classification of bodily exercises into gentle, moderate, and violent.

This division appears at first very logical and extremely easy to establish, but an attentive analysis is sometimes necessary to determine the real expenditure of force represented by an exercise. The estimation is often, and erroneously, based on the difficulty experienced in performing the work or on the fatigue felt by the muscles engaged. Now it may happen that the expenditure of force necessitated by an exercise is masked by the ease with which the muscular action is performed. It may happen that an insignificant work produces a lively sensation of fatigue. It is always easy, even to a very heavy man, to go up ten steps of a staircase. But he would often find it very difficult to go up ten rungs of an inclined ladder hanging by his hands. Still, if the vertical distance between the rungs and that between the steps is the same, the mechanical work is strictly the same in the two cases, for it represents an expenditure of force capable of raising the same weight through the same height. The fatigue experienced is however much greater after going up the ladder than after going up the stairs. This is because in the first case the work has been done by the small muscles of the upper limbs, and in the second case by the powerful muscular masses of the lower limbs.

Neither the difficulty of an exercise nor the local

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