In traditional Western exercise, you are encouraged to push through your limits. "Feel the burn." "No pain, no gain." "Pain is just a sensation." These thoughts may possibly be appropriate if you are a teenager learning Kung Fu and running bags of rocks up a mountain or playing barehand catch with concrete blocks. It is not appropriate for anyone else.
Tai chi (and qi gong) is entirely different. It took me a long time to realize this. I had to learn to relax and let go of tension. I had to learn how powerful tai chi can be at reshaping my body and mind without the tough exercise of Western exercise.
I am not an expert on traditional Asian medicine, but I believe other people when they talk about how qi flow affects our health. Pain indicates damage to your body and blocked flow. Tension blocks flow. Tai chi forms work your body and mind in ways that enhance the flow of qi and how it connects all parts of our body. It restores and strengthens flow.
Sun Lu Tang wrote a book, A Study of Taijiquan, in 1924. In it he said
"Those of you who are weak, who suffer from fatigue and injury or illness, or who have weakened your qi from the practice of other martial arts to the point that you no longer have the strength to train, all of you may practice tai ji quan. With practice, the qi will quickly return to a balanced state and will become strong, while the spirit naturally returns to a state of wholeness. Disease will be eliminated and the length of life increased." (Translated by Tim Cartmell, p. 60.)
If you feel any pain during your tai chi for health practice, you are not getting any gain. However, that is not to mean that you won't be working hard. You may be tired after practicing, but you should not feel any pain.
© 2012 Eric Borreson