The art of Yijinjing [“Sinew Changing Classic”] was passed down from the Zen master Damo, founder of the Shaolin school of martial arts. It is divided into an internal version and an external version.
　　The exercises of the internal version emphasize softness, using techniques of meditation and energy movement. It is not genuine Shaolin and should not be taught as such. Masters of it are unwilling to casually teach it to people anyway and guard it as a Shaolin secret. Martial arts practitioners who just want to look impressive are often practicing Shi’erduanjin [“Twelve Sections of Brocade”] instead, which has the same number of exercises and has similar principles but is actually a different art, and although they are related, they must not be confused for each other.
　　As for the exercises of the external version [the subject of this book], it emphasizes hardness, using techniques for building up the sinews and developing strength. This version has been widely spread, but I have not seen many authentic books about it. There are many versions of it to be found in bookstalls, but although they are all the same thing, there are actually huge differences between them. We may hope to find a definitive book, but there just isn’t one.
　　Generally speaking, this art is more popular in the north. The various exercises in this book are the secret teachings of Zou Zhongda, a pharmacist from Shanxi. According to him: “This is the true transmission of this Shaolin art as it was spread into Shanxi and Shaanxi. It is superior to the more common versions that have been published in books.” These exercises lay particular emphasis on the upper limbs, but are nevertheless an excellent means of training strength and the movement of energy, as well as stretching the sinews and vessels.
　　I have practiced these exercises diligently, four or five times a day. After the first few months, it boosted my appetite, my muscles and bones felt extremely comfortable, and various illnesses no longer threatened me. After a couple of years, not only was my body much healthier and my spirit full of vigor, my arm strength had increased so much that I could lift very heavyweights. My inherent disposition toward frailty, frequent illness, and inadequate strength had been fully conquered. A couple of years will be sufficient to sweep away frailty and make the arms capable of lifting hundreds of pounds.
　　Old age is going to reduce vitality anyway, but by conscientiously practicing this art, although it will not transform you into a young person again, it will nevertheless prevent illness and prolong life. An old practitioner of it in Jiangxi became known as “Clear Determination”. He is now eighty years old, but his spirit is still like that of a young man, and he walks ten miles every day without any difficulty at all. He said to me: “When I was middle-aged, my body was weak and often ill. A friend recommended to me that should I take up Yijinjing, so I did, and after practicing it diligently, I quickly became healthy. For forty years now, I have not yet been bothered by any illness, and I still walk with confident strides. If this isn’t because of Yijinjing, then what?” From this old man’s words, we can know the effectiveness of this art.
　　I am about to send my drawings and explanations for these exercises to the publishers
in order to send this art out into the world and share it with enthusiasts, and also to provide a means of correcting the errors in other books on the subject.
　　- written by Jin Ti’an