The common denominator I have found training with different instructors, who also were extremely effective using the techniques of their arts (some did represent a variety of different arts). There was a common factor. The way they used pain with their senior students instruction.
No they did not damage those individuals, it was not that kind of pain. But they used students who elected to train to severe levers attacking their instructor, and receiving much of the power of the defense being shown, unto pain itself.
What I discovered (often with pain myself) was those students in turn each became great instructors, because they ‘knew’ where to adjust your own efforts till they could feel that correct pain. And of course they also learned well how to do the same they were feeling. True skill.
Now I was never that skilled, Not that things were not openly shared with me, but those instructors knew my limitations, not being deeply trained in their arts, and chose not to often share that pain with me. So I did not get ‘it’ the same way.
And much being a youth instructor, I did not go to that level with the kids. Though there were times, that the movements we were studying did have an effect on the adults.
An interesting thing about Pain. Our body does not remember Pain, we remember we were I pain, but not the pain itself. Once experienced it goes away (in its own time)
Aikido for one was explained to me this way. You don’t move the person, (an art of locks and projections for the most part, which of course is an over-simplification) Rather it is pain that moves the uke into desired co\nmsequences. Intense pain feeling invoking reaction, or the feeling of anticipated pain causing the desired reaction.
Another way of looking at applications.