All organisms are in a constant state of purification – both spiritually and physically. Physically, the activity to throw off impurities brings on what we call “illness.” To put chemicals in the body (pain-killers, sleeping pills, and others) simply adds to the impurities to be thrown off and builds up the need for subsequent purification.
Spiritually, there is evolvement. Karma (the result of habit energies, vasanas, and tendencies, samskaras) causes us to have experiences that will hasten evolution or purifying of the Chi (Prana). When we do such practices as T’ai Chi Chih we are aiding this process.
The above is true, but only at one level. At the deepest, non-dualistic level it is not apparent.