Re: Aikido training - Why are you searching for internal strength?
As I trained and engaged in historical/political research into both Japanese history and aikido history, 3 things became clear to me:
1. Those instructors (including many of the uchi deshi and early aikido leaders) who I respect all have experience in martial arts outside aikido;
2. The current leaders in aikido and individuals who I respect have experience in other martial arts and much of the "new" instruction breaking into aikido is centered around larger martial concepts, some of which are better explained by other arts;
3. O'Sensei deliberately removed particular components of his aikido from the curriculum. In this sense, aikido as we know it is an abridged version of earlier aikido. I believe many of these missing components are found in other arts and could (in theory) be re-assembled into aikido.
Internal strength/internal power is one of those components no longer considered part of aikido curriculum. I believe Kuriowa Sensei refers to this concept as it relates to [true] kihon waza; Tohei Sensei also referred to it... Trouble is we don't do it in aikido so we need to look elsewhere.
I believe internal power is desireable to aikido because it is the root of our strength; i.e. I think internal power is what generates the energy we express into our partners. I think some of the IP people may be able to provide a more complete statement about why internal power is desireable to aikido...