Hmmmmm.
I agree with N2S about the center of percussion being the "sweet spot" where the most force can be applied, but it's not the center of mass. The center of mass is where the sword balances. The center of percussion is somewhere forward of that. The way I heard of finding it is to hang the sword pommel up and swing it like a pendulum, timing the sword's period (how long it takes to make one swing). You then take a string and weight (i.e. a real pendulum), and vary the length of the string until you get a pendulum that has the same period. The length of the pendulum is roughly the location of the sweet spot on the blade. Hopefully one of the physics boffins on this list will correct me if I'm wrong.
Another issue in hand shock is where the sword is gripped. This is more important on long-handled swords, like dhas. Basically, a sword is a rod, and as such, it vibrates when it hits something. The vibrations are similar to those on a guitar string, meaning they're the least at the ends, the middle, and the quarters (nodes), and strongest on the eighths between them (antinodes). The best way to experience is to get a stick (broom handle, dowel, whatever), and strike the end against the ground fairly hard while you grip it at various points. You can find the nodes pretty easily that way, and it sure teaches a proper grip. You can also do the same thing with a blade, although I advocate using the blunt and being a little more gentle
If you're holding the sword at the wrong point, or if the sword is designed badly, you'll grip near an antinode and get shocked each time the blade hits.
Hope this is useful,
F