By way of example, when Tibetan Crane is done correctly all the movements are natural and should not cause injury to yourself. However, in the process of learning the method it is inevitable that it will NOT be done correctly, probably for some time. It takes a lot of repetition and repetitious corrections from a teacher who knows what he/she is talking about, before the student is consistently doing it correctly. If you do it incorrectly for long enough, you will end up with wrecked knees, wrecked shoulders, and wrecked lower back. Proper instruction is important. This is an example of how the physical training can injure you if you try and go it alone, without good instruction. My example of Tibetan Crane is especially appropriate here because it is a method that, to most people, looks odd. People do not know what to make of it. So it is very easy to get it wrong.
Internal, or Qi-gong training carries the same risks, but they are more subtle. They sometimes require unusual breathing patterns that might put stress on the cardio-vascular system. The physical side of this stuff, like iron palm, requires quality dit-da-jow, the liniment used during and after sessions to heal properly, in addition to quality instruction. If you do not have the proper jow, or any jow at all, or lack quality instruction, you are asking for trouble.
The big problem is, signs of trouble might come very slowly until the damage has been done. You do not realize you are injuring yourself and might keep doing so for a long time. This is especially true with the internal training. Once that happens, you’ve got a problem.
I have a personal theory that perhaps all training such as iron palm may ultimately lead to injury, regardless of your jow and the quality of your training. It may be that in ages gone, people gained the benefits of such training in the short term, but the general hard life of a peasant in a world without modern medicine and sanitation meant that most people simply did not live long enough to realize the damage they were doing to themselves. In the modern age with modern medicine and sanitation and people living into their 70s and up, perhaps only now do we recognize the damage inherent in such training. We are living long enough for those subtle and gradual injuries to make themselves known.
@Krisxylove, I used
@Wing Woo Gar ‘s post as a tool to build upon with my thoughts, but this is simply to say that you are getting some good advice here: without good instruction you are likely to have a lot of frustration in your training, and some of it can actually be dangerous. I appreciate your enthusiasm, but if there is any way that you can, you must find a good teacher.