Nagamine Sensei shares an anecdote where he says that the "spearhand" was taught to the Japanese as a technique to be thrust to the middle. The original kata focused the spearhand on the eyes.
When the spearhand is directed to the solar plexus, I see it as more of a passing technique that sinks in an underhook for a throw. It's not a strike that I would practice and I think that even people "back in the day" would know better then that.
Agreed. I would never attempt to "spear-hand" someone in the solar plexus in a fight. That would be dumb. The "spear-hand" works well though when directed into the neck, the eyes, or the crease of the shoulder (just above the arm-pit in the front). Those are nice applications of the type that i refer to as "from the outside looking in"; meaning, what a non-martial arts practitioner would think if they saw this technique. A spear hand from kata/hyung appears to be an open hand finger strike to the solar plexus to someone who has never trained before. And it could be an open hand finger strike, just not to that target. Okay.
The application that I prefer, though, is the underhook mentioned by Maunakumu. If you consider the form Pinan Nidan, that technique is followed by a 270 degree turn into a knife-hand center. I would never have a reason to turn 270 degrees to face a new opponent. Not when turning 90 degrees is faster and would not require me turning through my blind spot. Indeed, 270 degree turns represent one thing to me: a throw or a grappling maneuver of some sort. Consider body-drops and hip-throws, they almost always require a turning maneuver of this kind.
So, to me, a good application for the "spear-hand" in Pinan Nidan is this: Following the arm-trapping and neck-striking movement of a knife hand technique, I step into the opponent and control their right arm with my left hand while my right arm snakes up and under their left arm, this is the set up for a hip throw, after which my arms are basically in the position of the knife hand technique. I also like using a neck throw here as well.
Regardless of how much you train you finger tips or try to focus your energy, striking into the solar plexus with the fingers just doesn't make much sense. Not that it can't be done, just that it would not be optimal, and when it comes to fighting for my life, I'll take what works best any day.
I saw a clip of a TKD Master breaking boards with a spearhand thrust. I guess if one learns to focus there KI they could take you out with a pinky finger.
