Letter to Steven Fox-Radulovich
The most vital element, abdominal breathing, consists of contracting the diaphragm and deep respiration. Inhalation, using abdominal and membranous muscles, and abdominal pressure, must consist of filling the pleura with air breathed in through the nose and creating a sense of lightly pushing such inhaled air down into the lower abdomen or tanden (the hypogastric area bellow the navel). The air inhaled must, without using the chest or throat, but through the force of constricting the lower abdomen, be expelled through the half-open mouth with the feeling that one is forcing it out from the tanden. When breathing in this way, it is absolutely forbidden to exert excessive strain.
One needs to be careful that excessive exertion does not lead to increased blood pressure and an inability to recover (from the Sanchin process). Exerting force on the upper part of the coccyx, adopt a forward-thrusting stance by way of abruptly flexing the pelvic region, and tighten the buttocks and the anus so as to gain a sense of the lower abdomen directly connecting with the anus.
About Breathing ("In" and "Yo" Breathing)
"Yin" and "Yang" exist in respiration. When one thrusts a finger into something hot, the cooling, reactive thoracic respiration that occurs is "Yin". Conversely, the abdominal breathing used to blow warm breath on the hands in cold weather is "Yang". All "martial breathing" is "Yang" respiration. Martial breathing consists of long exhalation and short inhalation. When performing Sanchin, first exhale for a long period, once the basic stance is adopted, then stop for about 3 seconds before inhaling deeply; once you exhale again, you have entered on the first form.