“During practice, you will feel very tired. When this happens, remember that tiredness is just a feeling.”

Chen Yingjun told me that when i was just starting my intensive practice with him in China.

In order to understand the broader meaning of this, it’s neccessary to emphazise the context. For the beginner, Taijiquan (tai chi chuan) is first and foremost a complete reeducation of his posture and way of moving, which is only possible with the guidance of a very competent teacher.

The first reaction of the mind to the postural corrections is one of strangement, since any change to a decades old habit, and specially one as deep as the body’s posture, usually causes surprise and discomfort. One of the ways the body and the mind use to avoid the discomfort is generating a feeling of tiredness, which tends to be overrated be the beginner. This is an emotional component that should be kept in mind.
Adding to that, when holding a posture after being correct by his teacher, the student demands a much higher than usual effort of his body’s muscle system, so it’s natural that the muscles tire up fast. The only remedy to that is holding the posture so the muscles get used to it.

On the other hand, the limitations imposed by the student’s physical conditioning need to be accounted for. Once holding the corrected posture and having reached his limit, the student’s natural reaction, if he tries to stay for too long, is degrading the quality of the posture so as too remove the strain from the muscles and forward it to the tendons and ligaments in the joints – which is a serious mistake. There’s no big problem in doing this for a short time, as long as one is trying to relax the body. That’s how one learns. However, even if one is trying to relax, it is not advisable to extend the posture holding too long after the limit is reached, because if one gets stiff, it could be counter-productive for the learning.
It is possible to overtrain, and it shouldn’t be done. Learning taijiquan (tai chi chuan) is not a matter of exerting towards the unbearable, this would only lessen the quality of the body posture and force the body to resort to undesirable ways and brute force.

We can say, thus, that there is one other subtle skill to be learned during taijiquan (tai chi chuan) practice: that of distinguishing a feeling of tiredness that should be standed, with the goal of getting stronger, and a real tiredness, the bodily limit which should be respected to avoid lesions in the joints. This is not a basic skill and it takes a while to acquire it, and specialized teaching is required for success.