"Still meditation includes: (1) The stillness of the Body (Yin), and (2) The activity of the Yi and Qi (Yang).
"In still meditation the physical body should be very still, relaxed, and calm. This opens the Qi channels and allows the Yi to lead the Qi strongly and without any stagnation. This stillness of the physical body is Yin. However, in order to build up the Qi and to circulate it strongly, the Yi must be strong and the Qi circulation must be alive and active. Therefore, the activity of the Yi and Qi is classified as Yang.
"(1) The Stillness of the Body includes: a) Light and Cold (Yin), and b) Heavy and Warm (Yang).
"During still meditation you will experience a different feeling. Normally, when you inhale, your physical body feels light and cold, and when you exhale, you feel heavy and warm. Naturally, all of these symptoms are closely related to the Qigong strategy, your breathing.
"(2) The Activity of the Yi and Qi includes: a) Yi is calm and peaceful, spirit is condensed (Yin), and b) Yi is excited and spirit is raised (Yang).
"When Yi is calm and peaceful, the spirit can be condensed and focused. The Qi circulates in the Conception Vessel and the six Yin channels, and it is condensed into the marrow and brain. However, when the Yi is excited and aggressive, then the spirit is raised. The Qi circulates in the Governing Vessel and the six Yang channels, and it expands to the skin." *
* Dr. Yang, Jwing-Ming, The Essence of Taiji Qigong