Which is what I said, earlier, regarding Yi-Chi-Li (but I seem to be under the Curse of Apollo...
). Yi (Shin) drives Chi (Ki)... which drives the body and the outward expression of physical power and waza. Kokyu assists in the creation of spherical force ("peng") by providing a little boost to the change in atmospheric pressure in body cavities, until the individual is able to use other means to create the structural force by other means (manipulating internal tissues instead of depending on kokyu).
The three internal harmonies - I notice that Yi and Shin are a little mixed here. In Chinese and Japanese it goes:
Chinese - 心与意合，意与气合，气与力合
Japanese - 心と意の合・意と気の合・気と力の合
Hope that makes it through...
Anyway, "shin" is "xin" - heart or mind, and "yi" is the intent part.