Re: Locking/pinning as pain submission...
From The Art of Aikido by K. Ueshiba, pg 70
...In Aikido we never start from a static position. Applying the principle of circular movement, the response to an attack is immediate, and the opponent never has a chance to get a firm grip. One movement flows into another until an attack is completely neutralized, and there are no fixed patterns to adhere to. Hence, in Aikido there are no complicated ground grappling techniques, no unusual chokes and holds, and no fancy kicks.
Similar to Jujutsu, in Aikido we have controlling pinning techniques, but in Aikido, unlike Jujutsu, the pins are never applied in a forced reverse direction. The holds and pins of Aikido are always applied towards the natural bend of the joint, using just enough pressure to render resistance futile. This use of a normal bend prevents unnecessary injury, and in fact works better than harsh, bone-breaking holds, which are difficult to apply.
...Solid ki breath-power, combined with an open mind and a strong body, will improve your character, the main goal of Aikido. This attitude is what most distinguishes Aikido from Jujutsu.
A useful definition of the difference between kiai-jutsu and aiki-jutsu would be: "in kiai-jutsu the mind follows the power of the body, and the force is expressed externally; in aiki-jutsu the body follows the power of the mind, and the opponent is controlled internally."