In dual rhythm we are apt to collapse suddenly after a movement. In fact, it is harder to control the release of the contraction of the muscles than to control the gradual increase of their contraction. This is illustrated in the difficulty of retaining breath. Breath is normally retained by sustaining the activity of the diaphragm, that is, its eccentric contraction. However, the body needs occasionally the complete surrender of muscles, but this should not be too sudden or jerky. The gradual surrender brings greater control and the higher type of development. When we use what are known as secondary movements, that is, when we use the hands to manipulate the stomach or when somebody else rubs us, we should restfully and completely give up the muscles and manipulate them or let them be manipulated in a state of rest. At times it may be well to manipulate a muscle when at full tension. When there seems to be a tendency to great constriction it may be well to manipulate a muscle during both contraction and relaxation and to test its relaxation. Again if a muscle does not seem to act as far as possible the opposing one may be found too short and may be manipulated to allow greater extension. 12. Practice thoughtfully. That is to say, study yourself. Observe your needs. For example, stand against some perfectly straight post or door, with the heels and back of the head against it. Where the back curves most, there will be room for the hand. Now where do you feel the most constriction? Give attention to such parts. Even when lying on your back, by stretching the limbs and expanding the chest such wrong tendencies or faults in standing can be corrected. The chest can be set free when it is constricted. When it is carried too low you can directly separate the breast-bone from the spine. By sympathetic expansions of the torso and by manipulating with the hands the parts that are especially constricted, curvatures, even in the back, can be improved. In all cases in practicing expansion we should be careful that there is no increase in the curvature of the spine. The back should remain normal, or become more nearly normal if we find any perversions. A hollow back, as is well known, is more difficult to correct than a hollow chest, though both of them are abnormal. A hollow back can best be corrected by the lifting of the feet, and the extension of the muscles of the back. If the hand is placed under the back where there is the greatest curvature there will be felt a normal action upon this curve of the spine. One point which has been discussed is whether training can affect the bones, or only the muscles. The whole body can be affected by training if the right methods are used. In correcting something like a hollow back, which has been of long duration, not only the balance of the muscles but the very articulations and ligaments and even bones may be affected by patient and persevering practice.