You don't need medical training or background to understand how the body is structured, just a desire to have an accurate understanding.
Is it easier to understand what Ki is than how bones, muscles, connective tissue, etc work? I can show you a picture of these things but not Ki. I can lead you to the people whose work is understanding how the body works with hands on experience (literally). They can give a concrete physical description of how it works. The trick is to keep the description simple.
The "Non-Aikido Traditions" is because the people leading those discussions are outside Aikido. When the non-Aikido people jump in and dominate a thread, you can bet that at some time the thread will most likely be closed.
If these discussions were led by people in Aikido using Aikido examples of what they are talking about then maybe the discussions would be mainstream.
Lets hear from some of the people in Aikido who can relate what they have learned ( as far as IS is concerned) to Aikido.
We are all doing IS.
IS is already in Aikido.
IS is a part of the human anatomy.
IS is a physical ability that in modern society is not as developed because of the work and life styles of modern times do no require it.
I think we are getting into a debate which is a reflection of semantics, because I don't think you and I are talking about the same IS.
The IS I am talking about has the POTENTIAL to be in aikido, but the methodology for truly developing it is not widely practiced in conventional aikido, at least not in the Aikikai or Yoshinkan groups that I am familiar with and have trained with. Ki society? Well, I haven't trained in a Ki society dojo. I did read Tohei's books and tried to replicate his exercises, and I do agree that the general gist is probably in the direction that I am training, but details seem lacking. Maybe not in the dojo, though, but I don't know from personal experience. So I could be wrong there.
The IS I am talking about is not a part of human anatomy, it is a skill set. As an analogy, I would not, for example, say that distance running is part of the human anatomy. I do think there are body structures which can be developed or connected to develop ability in IS.
While the IS I am talking about was most certainly developed in non-industrialized societies, you might want to talk to people like Phi, who practice the type of IS that I do but who grew up in non-industrialized societies and have stated openly that heavy manual labor does not develop that specific skill set. However, I do think that the mindset to train the IS I am talking about is extremely uncommon in the West. You have to be willing to not do some cool waza or get really any ego strokes for a long, long time and do a lot of boring, difficult training. I have shown a little of what I know (which again is at a very novice stage) to a number of aikido people in this country, and to a person, they have all said that they could see the merits but did not want to do the training. Too boring.
If you ever have opportunity to go to a seminar given by Akuzawa (the Aunkai guy) or Mike Sigman, but have not yet done so, I would strongly suggest it. I haven't trained with Dan H. (would like to) but suspect his power is similar- impressive, connected, non-local muscle use, etc, etc. There is no discussion that can really accurately convey the power that those guys generate. The hands-on experience affords an appreciation for the distinctions between the IS that people think is taught in Aikido and the IS that is based on body training (not technique/waza) methodologies that go way, way back before aikido, and which was in Ueshiba's aikido, but not transmitted widely or effectively.