Board breaking

Here is an article I wrote on board breaking, how it works and why it is done I hope it gives people some insight on why some arts place any importance on it.

Board breaking is common in the martial arts; the most commonly used material is pine. This material is selected because it has approximately the same tensile strength as human rib bone. Bones such as the femur and the humerus are many times stronger than the rib bone however. Boards are always broken along their weakest point which is with the grain. Boards never break across the grain because in that direction they are 5 times stronger, roughly the tensile strength of concrete. Boards, like concrete, are much more resistant to compression than they are in tension which is why they always break from the back of the board. Sometimes to save money boards will be glued back together, this however does not make the board easier to break but does in fact make it harder to break. This is because boards that have been glued together properly almost never break where they are glued and thus have to break at their second weakest point.

Some martial artists dispute the need for board breaking but others realize its importance. Breaking boards serves to improve confidence, demonstrate power, speed and/or accuracy. But the primary reason to break boards is to develop technique. Being able to break one board does not necessarily mean that you can break a rib it is more like if you can’t break a board then being able to break a rib is much less likely. Often when people, particularly children, fail to break a board with a certain kick they can often break it after they have worked on their technique. Once when I was assisting another instructor there was this child who failed to break with a flying side kick after 6 or 7 attempts. I was asked to work with him one on one on his technique. After 10 minutes helping him with his kick he got to try again… and broke the board on his first attempt.

When breaking multiple boards there are 2 basic approaches in the way they are stacked; using spacers or not using spacers. When boards break tension is applied to the back side of the board until the magnitude of the tension exceeds the tensile strength of the board and a crack is formed. The crack will then propagate to either end and towards the front of the board. When the crack reaches the ends of the board and all the way to the front the board breaks. It takes twice as much energy for a crack to propagate in 2 directions than it does in 1 so when performing a knife hand strike, for example, it is better to aim over to one side so that the majority of the energy only needs to travel one way.

Using spacers
Spacers are often used when breaking multiple boards to make the break more visually impressive to potential students or so that practitioners can break a larger number of boards. When 2 or more boards have spacers between them then each board can flex freely and break individually in sequence, to do this the momentum of the strike must be maintained over a long distance, this is not the correct way to apply force with a strike for a martial art. The important physical quantity for breaking boards is Impulse (J). This is the product of force (F) times the time taken (delta t).

J = F x (delta t)

This means that for a given magnitude of impulse less force is required if it is applied for a longer period instead of a shorter one. It has been calculated, by whom I do not know, that for each spaced board that is added to the stack makes the whole stack 90% more difficult to break due to the momentum of the boards above being transferred to the board below. In other words 2 boards are require 190% of the force required to break 1 board, 3 boards require 280%. What limits the amount of boards that can be broken is the momentum that is lost after hitting each board. The amount of power required to break each additional board is additive.

Not using spacers
Breaking stacks of boards that are unspaced is considerably more difficult because the amount of power required to break each additional board increases exponentially. It is a common belief that each additional board increases the amount of power required by a factor of 10. In other words 3 boards are 10 times harder to break than 2 and 100 times harder than 1. This is because each board below supports each of the boards above. Because each board breaks at the bottom first the force must be transmitted through the entire stack before any of the boards will break. All of the boards in the stack must break in sequence from the bottom up which would be similar to breaking one board that is a thick as the entire stack, except for the wood fibers between the individual boards that aren’t connected. This happens over a smaller distance than if the boards were spaced and thus at a faster rate and if the amount of impulse was the same as in the case of the spaced boards breaking the stack would require a much greater force. The amount of power required to break each additional board is multiplicative.

Speed breaks
These are where boards are held in the fingertips or thrown in the air before breaking. This can only occur when the force is applied over the smallest amount of time and hence the term speed break. The force on the board must exceed its tensile strength before the board can overcome its own inertia. If it does not then the board will just fly off without breaking.

Hand held versus using holders
In some cases boards will be held in human hands and in others in board holders, for downward strikes towards the floor, boards are almost exclusively held with board holders. It is more difficult to break boards held by human holders than by using board holders. This is because human beings always have some natural give in them while the board holders are more rigid. This means that for board holders only a small fraction of the force is absorbed by the rigid structure allowing more force to be available to break the boards. The use of board holders is good if there are you are on your own but it is more of a challenge to break with people holding the boards. It is difficult for human holders to hold 3 boards by themselves and any technique with the power to break 3 unspaced boards puts a large amount of stress on the wrists of the holders so they must be supported by other people holding the wrists. Holding 4 or more boards is next to impossible unless the holders have giant hands.
Breaking boards is a worthwhile endeavor so long as it is used for the right reasons such as developing technique and demonstrating the art. Board breaking for its own sake is counterproductive however as it takes time away that could be better spent elsewhere.

Talk amongst yourselves.

 

Board breaking is like many of the kung fu tricks. Awsome for show, very little to do with true martial ability. I do think it is great for the confidence of beginners though.

 

Real curious about some of your "facts" and figures. Good thing the "calculations" were done by "I don't know who."

 

Pine is often selected because it is soft and cheap, not because it most closely resembles "human rib bones". Tameshiwara is a decent exercise to get people to believe they can actually cause damage with their strikes. Other than some mild confidence boosting, it doesn't have much value as a training tool IMO.

 

Board breaking is a demonstration of accuracy. Thats it, really.

 

I still remember my first board breaking experience. I was 25 or 26 and taking Karate. The break was a side kick. I did my initial measuring kick (what ever you want to call it) where I just sort of slowly and mechanically executed the kick only with the intention of placing my foot on the board. It was about quarter speed with no power. I was about an inch too close and the board snapped on impact. I remember thinking "now I know what's up with this".

On another note, I see one more practical benefit to board breaking. My kids have done TKD and on some of the spinning kicks they just sort of spin with their foot flying around on the end of their leg and it's all good when they're hitting pads, but when they're hitting boards it hurts if they smack their ankle bone or the Achilles on the edge of the board and they are forced to focus more on the point of contact, correct form, etc.

 

Hahahha. I agree that's probably why pine breaking boards are traditional, but I think usually they're chosen because that's what you can buy pre-made from martial arts suppliers. :wink1: I guess I could go to Home Depot and get them to cut down some oak boards for me, but why?

I do think they have value as a training, though, beyond confidence-building. I doubt that breaking a board necessarily means that you can break a bone, but if you can't break a board then you definitely aren't going to be able to hurt anybody. Breaking a board shows that your strike is accurate, has decent form and is at least moderately forceful; if you half-*** it or are sloppy the board will just hurt you. (I'm assuming we're talking about 1" boards here - the 1/3" ones are practically balsa wood and are only good for speed breaks or small children.)

Also, like Dirty Dog says, it's fun and exciting. People should have fun and be excited about training.

 

Except that smacking your achilles tendon in can seriously injure you for a very long time. Thats not a lesson you want to learn in the first place.

 

Tensile strength of concrete is about 10% of its compression strength, seems to be about 300 psi, similar to the tensile strength of Eastern White Pine, at 305 PSI. That's with the grain, not across.

According to a material science textbook the strength of a pine board with the grain is about 18MPa (Megapascals), concrete is about 25MPa and a pine board across the grain is about 80MPa.

As energy is being transferred from the point of impact to the board, can you explain why it takes twice as much energy for a crack to develop in 2 directions?

I'm a little rusty on crack propagation, as far as I remember most of the energy in a crack is present at the tip of the crack, 2 crack tips means twice as much energy although the total energy required to break the board is the same. The 2 crack tips must push the board apart and create new surface areas and increase the surface energy.

f each stacked board makes the stack 90% more difficult, then only 10% of the original momentum is transmitted to the second board. Might want to check your math. Most people are taught to strike beyond the board(or boards).

Only 10% of the original momentum would remain if you only had enough to break 2 boards and no more. You do not use all of your momentum up when breaking boards, 2 boards being 90% more difficult means, for example (just a rough guess), if 1 board requires 1 Newton of force, 2 boards would require 1.9 Newtons with spacers and 10 Newtons without spacers. If you hit with 8 Newtons you would break the spaced boards but not the unspaced boards. If you hit with 30 Newtons you would break either stack easily.

I could find out who exactly performed the calculations you mentioned if only I had the time.

 

In your original premise, the amount of boards was irrelevant, as you stated each additional board adding 90% to the difficulty of breaking the stack. As you phrased it, each board makes it 90% more difficult to break a stack, if using spacers. Am I misquoting you? Have you considered that if you hit with 8 newtons of energy, and a board only requires 1 newton of energy to break, that your statement that a second board makes the stack 90% more difficult is incorrect? If you hit with 8 newtons, and the board requires 1 newton to break, does that not mean your second board will be struck with 7.1 newtons? Math can be your friend.


Who performed the calculations is not as revelant as what they actually mean. By the way, you have the time, this thread will not disappear any time soon.

 

Actually, when I did board breaking in the past, I did go out to Lowes' to buy lumber and basically cut it down to what I wanted. It was always a spur of the moment thing for me, and I didn't want to wait for delivery. Ha! I forgot people by them from MA suppliers!

 

Board breaking is nice and sure looks flashy at demos. But let's not lose sight of the fact that first and foremost, it's a teaching tool.
By breaking boards, the student is working on timing, distancing, focus and most importantly, confidence. The student has to have good technique to accomplish the break; Mr. Board :s118: will very quickly point out bad technique.

We have a saying: it never hurts to break a board. It only hurts if you don't break the board.

 

Mr Board is a great teacher.

 

Board breaking was originally a means of demonstrating one's dilligence with the makiwara. Very few dojos in the states incorporate makiwara training into their curriculum.

I have heard (and on occasion proferred) the arguments for accuracy and technique, and while I agree with them, I also feel that there are better ways to both develop and test a student's technique. In the beginning, it can be a huge confidence builder, and of course it makes a great demonstration tool. As Dirty Dog said, it's fun.

I have no position on it one way or the other, aside from that if you're going to incorporate board breaking into tests, use full sized boards for the grown ups.

 

I always wondered if board breaking, in some instances, encouraged bad practices.

For example, downward strikes. Now, I don't know how power is generated in most forms of Karate, but in my art, it's important that the "ground" is behind our strike; the elbow is underneath the fist, the body and stance is underneath the elbow, and the ground is underneath the body. However, if you're breaking something by striking down, aren't you using only your upper body strength, and getting absolutely no help from the stance and the ground?

As I said, most forms of Karate are probably different, but even in Karate, I'm sure that engaging your lower body when striking is important, is it not?

 

Depends on whether you are striking from a standing or kneeling position.

 

Never done any board breaking, nor do I see the need.
However to each his/her own.

 

But then how will you defend yourself when attacked by a tree?123