Chi (Qi)

Flowing through the body is Qi (Chi) or energy. It runs along a complex series of pathways, known as meridian lines, closely related to the nervous and vascular systems, connecting all parts of the body. The Qi is found at a molecular level. A western parallel might be the force that holds the particles in an atom in orbit around each other

When the Qi runs throughout the whole body freely at optimum levels, the body and mind is at its best and most efficient. This is achieved when perfect equilibrium is found; yin and yang, a balance of relatively more active or outward forces, and relatively more passive or inward ones.
This does not just relate to the physical body, but to the mind as well (many imbalances, and sicknesses stem from the brain, including stress). A number of practices including Taijiquan and Qigong use these principles.

Taijiquan (Tai Chi Chuan) uses breathing and whole body movement to circulate and revitalise both body and mind by working with Qi energy. The movements of the exercise (martial art) improve physical balance, flexibility and fitness.
The standing post meditation that we also do in the class also helps to strengthen the body and mind by cultivating Qi energy.
The first is relatively Yang, the latter relatively Yin so they are complimentary. As we practice both side by side it may be interesting to explore the similarities, differences and how these change from time to time whilst you are working with them.
It may help to understand what Tai Chi is really about by going back to its roots and the principles of the Chinese approach to health. Around the sixth century BC, Lao Tsu, an older contemporary of Confucius, created Taoism, a reflective philosophical treatise upon a way of living.

This was split up into eight areas, or Taos, which were ways of living one's life according to various principles, including that, amongst others, the Tao of Revitalisation.
This Tao is what provides the fundamental basis of Chinese medicine including Taiji - that of Qi.
The Chinese believe that as well as the body being made up of individual organs, they interact with each other on a global or holistic level - a fundamental interconnectedness of all (Twentieth Century Western physics has a parallel with aspects of quantum physics). If a particular organ is sick, never look only at that organ, but at the whole body to find the cause so it follows that the preventative treatments like Taiji work on the body and mind as a whole too.