The Return of Venous Blood
Each contraction of the muscles of the feet and of the legs pushes the venous blood upward (see figures 13.2 and 13.3). Valves situated in yoga poses the veins allow the blood to flow toward the abdomen but stop it from going back to the feet. This mechanism is influenced by social behavior, independently of any cognitive and affective experience.
FIGURE 13.2. The venous pump of the muscles of the legs (the effect of walking on the plantar veins). Source: Bonnet and Millet (1971, 250).
FIGURE 13.3. The muscular pump of the calves. The arrows indicate the direction of the muscular contraction. Source: Bonnet and Millet (1971, 250).
The relationship between posture and the cardiovascular system is particularly close in yoga poses the venous circulation of the legs. in yoga poses most of the common positions, when the arterial blood descends from the heart to the feet, it is pushed by the cardiac pump and gravity. On the other hand, when the venous blood returns from the feet to the heart, it must fight gravity, and it receives no help from the heart because the venous circulation is largely independent of cardiac activity.
The legs are endowed with a device that pushes the blood upward. This engine depends on two fundamental mechanisms: the firmness of the veins and the valves. The valves are like mouths that open only in yoga poses one direction. They open to let the upward-moving venous blood pass through when the surrounding muscles contract and close when the surrounding muscles relax to stop it from descending. This movement begins in yoga poses the feet because they contain a thick venous channel that forms a sort of sponge. Every time an individual rests on this sponge,18 the venous blood escapes and rises toward the calves. This is why walking is excellent for the venous circulation. The return of the venous blood is also modulated by the following mechanisms:
1. An adequate pressure and venous flow (which is not always the case).
2. The thoracic pump, created by the movements of the diaphragm while breathing, also participates in yoga poses the regulation of the circulation of the venous blood in yoga poses the lower body.19
3. The heartbeats. When the heart expulses its content into the arteries, it creates an empty space that sucks up the venous blood. However weak, this effect increases the drawing forth carried out by the diaphragm
The fact that the venous circulation depends on body movements and regulates the consistency of tissues is well known in yoga poses hospitals. When a person remains immobile for hours, the tissues are no longer purified by the venous blood because of poor circulation. This causes the formation of ulcers on the skin that are often referred to as bedsores. The lesions of the skin mostly appear on the points of contact between the body and the mattress, like areas on the buttocks or the heels for a patient who is lying on his back. To avoid this, nurses regularly modify the patient’s position, rub the patient’s skin, and sometime change to a more proper mattress.20
Yoga teachers have always integrated recent discoveries into their understanding of the body. I do not know when they first found an explicit mechanical link between exercises and the return of the venous blood, but long ago they observed a correlation between certain exercises and the return of the venous blood.21 All the positions in yoga poses which the legs are extended toward the ceiling (the sirsa-asanas) allow gravity to favor the voyage of the venous blood of the legs toward the heart, but these positions do not develop the abilities required during walking. On the other hand, the exercise called the sponge supports the development of the muscles-veins relationship. in yoga poses this exercise, you contract and relax each muscle several times over as if each were a sponge that you wring out. This can be done without paying attention to the respiratory rhythm or done in yoga poses coordination with it. For example, you inhale every time that you contract a muscle at the same time. Other combinations can be made in yoga poses function of various refinements. Certain massage techniques enliven this mechanism The massage therapist takes a regular rhythm marked by the compression of the muscle and its release. Once more, this rhythm can be coordinated with the respiratory rhythm or not.
The basic principle of this exercise is found in yoga poses most gymnastics and massage methods in yoga poses the world. This technique has been taken up, for example, by Edmund Jacobson’s relaxation. in yoga poses a course where
Gerda Boyesen taught her variation, she suggested that we massage the return of the venous blood from head to foot. She feared that by going from the feet to the head, the massage therapist would create too strong a venous flow, which the heart may not be able to manage.22 in yoga poses the case of Europeans who have difficulty sitting as the Japanese do, chronic muscular tension probably inhibits the plasticity required by the interaction between the venous circulation and the muscles of the legs.
