This is from George Hackenschmidt: The principal food for man is pure air. Partake of it as much as you possibly can. Breathe much, and as deeply as you can, through the nose. Breathing through the nose is the only proper way of respiration, and at the same time, an important regulator for the movement of the body. For if, for any kind of work, the breath through the nose ceases to be sufficient, one ought to either discontinue the work or restrict the movement until breathing has again become normal.