It is then from within outward that the force capable of expanding the chest acts, and it is in reality to the lUngs and not to the muscles that the chief share in the changes in form and size of the chest belong. The most powerful inspiratory muscles can not raise the ribs, unless the lungs participate in the movement of expansion, and, on the other hand, the lungs can raise the ribs without the aid of the muscles, for the chests of emphysematous patients remain vaulted in spite of their efforts to lower the ribs and complete the expiratory movement.
If we sum up the facts we have just enunciated, we shall be driven to the conclusion that, in order to raise the ribs and get rid of the vicious conformation of flat chest, we must not seek to act directly on the thoracic muscles, but to produce as extensive respiratory movements as possible.
There are two methods of amplifying respiration: one consists in voluntarily expanding the thorax in all directions. This method is in the domain of "chamber gymnastics"; it has been much extolled, and it may give good results. The other method comes more directly into the field of our studies. It consists in increasing by exercise the amplitude of the respiratory movements.
The problem has now become clear and definite. We need, in order to develop the chest, to know what exercises are most fitted to produce a series of very extensive respiratory movements. Now, the amplitude of respiration, as well as its frequency, is in direct ratio to the intensity of the respiratory need, and we know that the intensity of this need depends on the quantity of mechanical work performed in a given time.
The exercises which cause an accumulation of work are, then, those most fitted for increasing the size of the thorax, and for demanding increased work from the lungs. And we know that this accumulation of work occurs especially in exercises of strength and speed.
Thus the mechanism of exercise, its performance by the aid of these muscles or of those, are of secondary importance in producing the result of which we are speaking. It matters little by what process the muscular force is expended, provided that there is great expenditure in a short period of time. It is indifferent whether the movements are very slow, each of them representing a great number of kilogrammetres, or whether they are extremely rapid, each movement representing but a moderate effort. It is merely necessary that the sum of work represented by these movements, whether few or many, should be considerable in a short time.
Now, the quantity of work which a given muscular group can perform in a given time is subordinated to the strength of this group. There are muscular groups which are too weak to ex-
