"The Chinese have long believed that the universe is made up of two opposing forces- Yin and Yang- which must balance each other. When these two forces begin to lose their balance, nature finds a way to re-balance them.
"The Chinese have classified everything in the universe according to Yin and Yang. Even feelings, thoughts, strategy, and the spirit are covered. For example, female is yin and male is Yang, night is Yin and day is Yang, weak is Yin and strong is Yang, backward is Yin and forward is Yang, sad is Yin and happy is Yang, defense is Yin and offense is Yang.
"When it is said that Qi can either be Yin or Yang, it does not mean that there are two different kinds of Qi like male and female, fire and water, or positive and negative charges. Qi is energy, and energy itself does not have Yin and Yang. When it is said that Qi is Yin or Yang, it means that the Qi is too strong or too weak for a particular circumstance. It is relative and not absolute. Naturally, this implies that the potential which generates Qi is strong or weak. In any discussion of energy where people are involved, Human Qi is used as the standard.
"When we look at Yin and Yang of Qi within and in regard to the human body, however, we must redefine our point of reference. When discussing Qi within the body, the reference point is the normal healthy state of the Qi there. If the Qi is stronger than it is in the normal state, it is Yang, and if it is weaker than this, it is Yin. There are twelve parts of the human body that are considered organs in Chinese medicine, six of them are Yin and six are Yang. The Yin organs are the Heart, Lungs, Kidneys, Liver, Spleen, and Pericardium, and the Yang organs are Large Intestine, Small Intestine, Stomach, Gall Bladder, Urinary Bladder, and Triple Burner. Generally speaking, the Qi level of the Yin organs is lower than that of the Yang organs. The yin organs store Original Essence and process the Essence obtained from food and air, while the Yang organs handle digestion and excretion.
"When the Qi in any of your organs is very much off from its normal state, you may become sick. The Qi in your entire body will also be affected and you will feel too Yang, perhaps feverish, or too Yin, such as weakness after diarrhea. Your bodies Qi level is also affected by natural circumstances such as weather, climate, and seasonal changes.
"Breath is closely related to the state of your Qi, and therefore also considered Yin or Yang. When you exhale you expel air from your lungs, your mind moves outward, and the Qi around the body expands. In the Chinese martial arts, the exhale is generally used to expand the Qi to energize the muscles during an attack. Therefore, you can see that the exhale is Yang- it is expanding, offensive, and strong. Naturally, based on the same theory, the inhale is considered Yin.
"Your breathing is closely related to your emotions. When you lose your temper, your breathing is short and fast, i.e., Yang. When you are sad, your body is more Yin, and you inhale more than you exhale in order to absorb the Qi from the air to balance the body’s Yin and bring the body back into balance. When you are excited or happy your body is Yang, and your exhale is longer than your inhale to get rid of the excess Yang which is caused by the excitement.
"As mentioned before, your mind is also closely related to your Qi. Therefore, when your Qi is Yang, your mind is usually also Yang (excited) and vice versa. The mind can also be classified according to the QI which generated it. The spirit, which is related to the Qi, can also be classified as Yang or Yin based on its origin.
"Do not confused Yin Qi and Yang Qi with Fire Qi and Water Qi. When the Yin and Yang of Qi are mentioned, it refers to the level of Qi according to some reference point. However, when Water and Fire Qi are mentioned, it refers to the quality of the Qi." *
* Dr. Yang, Jwing-Ming, The Essence of Taiji Qigong