If the standing position has to be maintained for any great length of time, one foot should be placed slightly in advance of the other, the weight being borne upon the straight leg and the active supporting foot, the other being relatively passive. This asymmetric position has the important advantage that the two extremities may be brought alternately into play. The most common defect in standing is that the entire weight is usually borne upon the same leg, generally the right one, while the left, being inactive, is placed out to one side; the habitual maintenance of this position leads, as we shall see later, to a tilting of the pelvis to one side, with a consequent spinal curvature and lowering of one shoulder. Persons with strong feet, especially primitive unshod feet, mountaineers, runners, and young children, walk with the inner borders of the feet nearly parallel to each other and the direction of motion. The best sculpture, both ancient and modern, shows the straight supporting foot, which in standing is not necessarily parallel with its mate, since the resting foot may assume almost any angle of divergence. The influence of the stability of a correct base is well illustrated by standing on one foot and swinging the other leg backward and forward, which is much more difficult if the supporting foot be turned to one side. A runner finds it very difficult to run with the toes turned out, although the heels never touch the ground. =Corrective Exercises.=—Many of the most common defects, such as a drooping head, round shoulders, flat chest, beginning spinal curvature, etc., result from a weak and relaxed condition of the muscles, whose function it is to move and support these parts. If the head is constantly bent forward in studying and writing at the desk, the muscles at the back of the neck gradually lose their tone, and stretch out like a piece of elastic that is constantly kept on the strain. The exercises selected must be such as will strengthen these particular groups of muscles, and, while taking the exercises, the entire attention must be concentrated on the part being exercised. Any lack of symmetry in the chest, spinal curvature, or actual weakness of the lungs will necessitate the prescribing of special and carefully selected exercises. As to the exercises themselves, they should be so arranged as to bring into play in a methodic manner all the muscles. All special and corrective work must be supplemented by general work, which will increase the organic vigor of the heart, lungs, and chest necessary to meet the vital demands of the whole system. Games are, of course, most useful for this purpose, but the games should not be too violent. In most free exercises the limbs are used for weights of resistance. In a man weighing one hundred and fifty pounds the arms usually weigh about ten pounds each and the legs twenty pounds.