This started out as an exploration of Internal Strength and while I am still not sure if it is about internal strength. I think it is more correctly about the biomechanics of throwing. (See How to Throw Someone for videos of this and other concepts in action)
Internal Strength - what is it?. Ask half a dozen experts and you get half a dozen answers. Whatever the answer, its clear it has a role to play in doing good aikido. There seem to be a variety of methods to getting it - though not all agree on who has it and who doesn't. For this aiki-bunny it seems to me some understanding can be gained from a biomechanics approach. It's a step beyond aikiphysics, which has been limited to static analysis.
In a casual scientific approach it starts with a review of what's out there (I am trying to communicate and grab the wrists of these people and their students as I can) and then working from a really simple biomechanical model through to application to technique to help shed some light. It's a living document and not filled out yet...but a starting point - albeit autobiographically nonetheless.
CAVEAT: In adopting a western scientific approach using the tools of physics and its human-motion derivative of biomechanics, we start at the other end of the spectrum from the eastern traditions. The method attempts to move from the known to the unknown using deductive reason. The eastern approach (somewhat simplified) is to observe something, give it a descriptor and transmit it in this way. Without the cultural context it can be difficult to get a handle, so perhaps this viewpoint is useful.
While writing this is cathartic and helpful, I would really value the feedback of others and will happily credit content where helpful.
Finally 2013 I got some hands on training with an established SI lineage. here's the write up