The function of breathing is a vital one, and it immediately concerns the continuance of life. We can live many hours without sleeping, and many days without eating or drinking, but only a few minutes without breathing. The act of breathing is involuntary, but the manner of it, and the provision of the proper conditions for its healthy performance, falls within the scope of volition. Man will continue to breathe involuntarily, but he can voluntarily determine what he shall breathe, and how deeply and thoroughly he shall breathe; and he can, of his own volition, keep the physical mechanism in condition for the perfect performance of the function.
It is essential, if you wish to breathe in a perfectly healthy way, that the physical machinery used in the act should be kept in good condition. You must keep your spine moderately straight, and the muscles of your chest must be flexible and free in action. You cannot breathe in the right way if your shoulders are greatly stooped forward and your chest hollow and rigid. Sitting or standing at work in a slightly stooping position tends to produce hollow chest; so does lifting heavy weights—or light weights.