The Yi Jin Jing or muscle tendon changing classic is credited with being gifted to the world in 527 AD. This is arguably one of the most famous sets or Qigong forms that has been created. Shamanic Qigong forms do predate this form, but its popularity as both a spiritual and martial set have played largely in its popularity.
So a cliff-notes version of this origin is that Bodhidharma arrived at one of the Buddhist temples and found the monks to be frail and weak from extended meditation practice. At this time I have read that the Buddhist perspective during that time was that the physical body held little relevance in comparison to the pursuit of spiritual enlightenment.
Seeing his spiritual family this way deeply upset/disturbed Bodhidharma, and he went into seclusion. For 9 years he contemplated and tried to find an answer to the dilemma. When he returned he had developed the muscle tendon changing classic, and the bone marrow washing set. I have shortened and simplified this story because of how many people write books about it. I would recommend for further reading Dr. Yang Jwing-Ming’s book the roots of Qigong, which leaves no stone unturned. His writing is very in depth I really enjoy the amount of research in his writing. I have corresponded with him regarding this study and he responded to email, which I have not experienced with an author before. Even though wickepedia is not a valid academic resource, its entry for the Yi Jin Jing is an easy read and has a large amount of information that I Have not seen any major discrepancies with.
This being said the form has multiple variations now , and the one that I will be training is the form as endorsed by the Chinese health qigong association, their books cut to the chase and the training material they have is wonderful. (Sections on clearly illustrated/demonstrated do’s and don’ts including where gaze should flow and common mistakes)