"Breathing is considered the strategy in Chinese Qigong. How you coordinate your breathing allows you to regulate your body and lead your Qi efficiently. There are two ways of breathing which are commonly used in Taiji. The first way is called “normal abdominal breathing”, also sometimes called “Buddhist breathing,” while the other way is called reverse abdominal breathing”, also sometimes called “Daoist breathing.” In normal abdominal breathing, when you inhale the abdomen (or Lower Dan Tian) expands, and when you exhale the abdomen withdraws. However, in reverse abdominal breathing the abdomen (or Lower Dan Tian) withdraws when you inhale, and expands when you exhale. It is usually easier to keep your body relaxed and feeling comfortable with normal abdominal breathing, so that is the method commonly used by those who practice Taiji only for health.
"As for reverse abdominal breathing, many Taiji practitioners today falsely believe that the reverse breathing technique is against the way of the Dao. This is not true. It is simply used for different purposes. Try this simple experiment. Place one hand on your abdomen, and hold the other in front of you as if you were pushing something. Inhale deeply, and as you exhale, imagine that you are pushing a heavy object. You will easily see that, when you try to push as strongly as possible, you automatically use reverse breathing. This is the method which is commonly used in weightlifting competition. The competitors often wear a thick belt to support their abdomens and increase their power.
"The rationale for reverse breathing is quite simple. You can lead a much strong flow of Qi to the limb and manifest more power if you also, simultaneously, direct another flow of Qi to your Lower Dan Tian. This is in accordance with the basic laws of physics which states that for every action there must an equal and opposite reaction. If you are still not convinced, try another experiment. Blow up a balloon, and hold a hand on your abdomen to see how it moves.
"You can see from these experiments that reverse breathing is in accord with the Dao. It should be used whenever you need to lead Qi to the limbs to efficiently manifest power, as when you are fighting. Because it expands the Qi and energizes the body it is considered Yang in comparison to normal breathing.
"(1) Normal Breathing includes: a) Inhalation (Yin), and b) Exhalation (Yang).
"In normal breathing, inhalation is classified as Yin because the Qi is led from the limbs to the Lower Dan Tian, and exhalation is Yang because the Qi is led to the limbs.
"(2) Reverse Breathing includes: a) Inhalation (Yin), and b) Exhalation (Yang).
"Similarly, in reverse breathing, inhalation is classified as Yin because the Qi is led from the limbs to the Lower Dan Tian and from the skin to the bone marrow. Naturally, the exhalation is Yang because the Qi is led to the limbs from the Lower Dan Tian and to the skin from the bone marrow." *
* Dr. Yang, Jwing-Ming, The Essence of Taiji Qigong