This demonstration was in Waynesboro, PA. in 2011. Each break is one inch.
The motion analysis brings up some interesting points. It should be noted:
1. Reciprocating motion is made from essentially the same beginning position. One fist is up, body turned at the waist, one fist crosses low.
2. The force emanates from the twist at the waist.
3. There is no windup or reaching extension and the shoulders remain level*.
4. Some part of the fist is the breaking element of the strike**.
* Being aware that the success of the board breaking is not the sole purpose of the demonstration but an element in the process of verifying the creation of effective technique. The aspiration of practice is to have the technique work for all the reasons it should, not to resort to a less efficient and in the long run, self damaging technique to get the job done.
** The low block, high block, and the out > in block are being struck by the muscle of the pinky side of the fist. The inside > out block is with the knuckles. Intention and application of effective force should be done with some portion of the hand striking. Students should note practice with partners is done with the back of the hands and or wrists for safety.
More on blocking movement: