Mike Sigman has a blog,
http://mikesigman.blogspot.com/, on Internal Strength (and it's not about spiritual thing). There are good information to read and comprehend to the willing. Much of Sigman stuffs referenced older Chinese sources, but they are more than relevant to aikido and other martial arts if you stretch your imagination a little bit (not much, just a bit). Sigman tends to focus on logic, math and physical and biological sciences to discuss these stuffs, which i believed, it won't bode well with aikido folks, since those things have no place in our aikido practice, damn it! (yes, it was a tongue-in-cheek thing). So if you have some free time from discussing bridge over trouble water and should aikido folks jumping up and down yelling "Kill! Kill!", you can swing by the blog and check it out and please try not to sink to deep into the peat.
Enjoy!
