Hey Shinzu,
I wrote up this stuff on the BudoSeek forum about board breaking. Its my general opinion on the topic. For everyone whos seen it on BudoSeek, just ignore this post, nothing new. First is the purpose of breaking, second is an analysis of breaking with spacers.
There is a fundamental question as to the point of Tamashi Wari (breaking training, (Japanese)). It can seem like breaking a board or any sort of material has little relevance to striking real live people. How applicable is such a methodology that approximates materials like wood and stone to human bodies?
I don't think the comparison of the human body to other materials ever was, or ever is, the essential value of Tamashi Wari. Definitely breaking materials is a very poor approximation to hitting a person. But I think that thoughts along this line are a fallacy and are not along the line of the true purpose and value of Tamashi Wari.
For me, and it took me awhile to see this, breaking things have very little to do with the actual breaking of them. Rather it has everything to do with the amount of force applied.
Tamashi Wari is not about training to be able to break large piles of hard substances. Its primarily about force output, and by force output I don't mean trying to maximize the force in a strike. Increasing the strength in striking is a fine thing, but Tamashi Wari training has nothing to do with that.
Breaking is about applying a specific amount of force to a substance to break it and hopefully nothing exceeding that amount. Its all about learning how to strike with varying force. Its main concern is the controling of the power of the strike. Such that the practitioner has total control over the amount of energy leaving the body.
Beyond this, there is a conditioning aspect to the striking surfaces. Jawbones and knees may be approximated much more accurately to hard materials then other areas like the diaphram.
Now it could be asked why would anyone want to hit someone with less then the maximum amount of force possible? The best answer is conservation of strength. These martial arts were designed in feudal nations, meaning that hand to hand (weapon to weapon) combat was the primary means of warfare. When you are in a battle against hundreds and thousands of people, that could last anywere from an hour to many hours, conservation of strength is what's going to keep you alive and able to kill.
A modern day illustration would be fighting a group of people. If you have to go through 10 to 20 guys, hitting each one with maximum force, how strong are your strikes going to be by the time you get to the last one?
Besides the fact that strikes done correctly and targeted correctly need no where near full power to incapacitate most foes, strikes done at full power are very lethel and while this was not as great a concern in feudal times, its a very real concern today.
I think that the most skillful way to break something is with the least possible amount of energy. For example a hanging board, breaking it so that the broken piece of the board falls straight down would be the most skillful strike. Breaking it so that the piece flys through the air in a downward arch is the easiest way.
I believe that training to break the greatest amount of material misses out on the whole point of breaking in the first place. It is much more beneficial for students to break just 1 board over and over again, learning how much force is needed, then it is to just sit a stack in front of them and constantly drive them to break larger and larger piles. Breaking a constant amount of material, over and over again until you know exactly how much force should be applied to break it, that is the greatest training in my opinion.
Breaking has gotten labeled as a means of gauging strength and martial skill, but it should never be used as such in a training environment. The one who can break the most is not necessarily the greatest.
I would think the purpose of breaking things in public consists of wowing a crowd and gathering attention. Which isn't a bad thing (as long as spacer's are not used, LOL).
All this being said, there is a very real danger involved in Tamashi Wari. If the strikes are not done correctly bones can be broken.
As stated in the other post about breaking, tremendous confidence can be gained when kids get to break things. And when supervised, the risk of injury is drastically reduced. Statistacally I would bet that most injuries in breaking are due to oversized ego's breaking by themselves on their own and then for of public glorification.
Breaking with Spacers:
Board breaking with spacers defeats the purpose of breaking.
Spacers - even the width of a toothpick - drastically reduce the force required to break the boards (or blocks/bricks).
It appears to the audience as if the breaker has broken much more material then they actually have.
The physics of this was documented in the 1970's by physicists studing the martial arts. How it works is that when boards or whatever are separted by a spacer, the first board breaks, then the pieces of the broken board are propeled in a downward velocity. These 2 pieces of the board hit the board below it at nearly the same time the hand (or whatever striking surface) hits the second board, so that the force of the downward projected pieces add to the force of the strike.
So that the total force exerted on the second board =
Force of strike after breaking first board + Force of broken pieces of the first board.
This effect, of the board above striking the board below, continues like a domino effect throughout the entire stack of boards.
By the end of the break as much as approximately 40% (I'm not exactly sure on the percentage, it was from the article I read, that was about 3 years ago) of the force required to break the boards comes from the force of the board above striking the board below, thus the actual amount of force needed from the strike itself is only around 60% of what it should be to break the boards.
Really, breaking with spacers is like breaking 1 board, then a second board, then a third, etc.. Rather breaking without spacers is really breaking 4 boards (for example). If someone broke 9 boards with spacers, they did not really break 9 boards, they broke a single board 9 times in one strike, which requires much much less force then breaking 9 boards that are all flush side by side.
This makes the strike look much more powerful then it actually is to audiences, in truth deceiving the audience about the power of the strike and the relative effectiveness of the art in question.
Spacers should never be used by any school, they do nothing but puff up the school and have no value in training. They waste wood and other materials. They are in effect a method of faking a powerful strike used by schools of little martial value.
Instead of breaking 5 boards with spacers, just break 2 or 3 without.