Sprint running is only an exaggeration of the system displayed in long-distance work. The arms rise as in fast walking, and for the same reasons, till they are doubled up. The work, being fast, requires that the lungs be kept expanded, therefore the arms are kept stiff and rigid to aid the chest muscles in holding out the walls of the thorax to give room to the lungs. The distribution of weight, on account of the rapid motion, comes to be much the same as in fast walking, but the knees are bent of necessity; because in running the progression is made by springs from toe to toe, instead of heel to heel. The same cause admits of the upper part of the body falling forward, though the elevation of nose and hollowing of back is even more important than in long-distance work, inasmuch as the exertion is more severe while it lasts.